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1 | libpng-manual.txt - A description on how to use and modify libpng | 1 | libpng-manual.txt - A description on how to use and modify libpng |
2 | 2 | ||
3 | libpng version 1.5.9 - February 18, 2012 | 3 | libpng version 1.5.9 - February 18, 2012 |
4 | Updated and distributed by Glenn Randers-Pehrson | 4 | Updated and distributed by Glenn Randers-Pehrson |
5 | <glennrp at users.sourceforge.net> | 5 | <glennrp at users.sourceforge.net> |
6 | Copyright (c) 1998-2011 Glenn Randers-Pehrson | 6 | Copyright (c) 1998-2011 Glenn Randers-Pehrson |
7 | 7 | ||
8 | This document is released under the libpng license. | 8 | This document is released under the libpng license. |
9 | For conditions of distribution and use, see the disclaimer | 9 | For conditions of distribution and use, see the disclaimer |
10 | and license in png.h | 10 | and license in png.h |
11 | 11 | ||
12 | Based on: | 12 | Based on: |
13 | 13 | ||
14 | libpng versions 0.97, January 1998, through 1.5.9 - February 18, 2012 | 14 | libpng versions 0.97, January 1998, through 1.5.9 - February 18, 2012 |
15 | Updated and distributed by Glenn Randers-Pehrson | 15 | Updated and distributed by Glenn Randers-Pehrson |
16 | Copyright (c) 1998-2011 Glenn Randers-Pehrson | 16 | Copyright (c) 1998-2011 Glenn Randers-Pehrson |
17 | 17 | ||
18 | libpng 1.0 beta 6 version 0.96 May 28, 1997 | 18 | libpng 1.0 beta 6 version 0.96 May 28, 1997 |
19 | Updated and distributed by Andreas Dilger | 19 | Updated and distributed by Andreas Dilger |
20 | Copyright (c) 1996, 1997 Andreas Dilger | 20 | Copyright (c) 1996, 1997 Andreas Dilger |
21 | 21 | ||
22 | libpng 1.0 beta 2 - version 0.88 January 26, 1996 | 22 | libpng 1.0 beta 2 - version 0.88 January 26, 1996 |
23 | For conditions of distribution and use, see copyright | 23 | For conditions of distribution and use, see copyright |
24 | notice in png.h. Copyright (c) 1995, 1996 Guy Eric | 24 | notice in png.h. Copyright (c) 1995, 1996 Guy Eric |
25 | Schalnat, Group 42, Inc. | 25 | Schalnat, Group 42, Inc. |
26 | 26 | ||
27 | Updated/rewritten per request in the libpng FAQ | 27 | Updated/rewritten per request in the libpng FAQ |
28 | Copyright (c) 1995, 1996 Frank J. T. Wojcik | 28 | Copyright (c) 1995, 1996 Frank J. T. Wojcik |
29 | December 18, 1995 & January 20, 1996 | 29 | December 18, 1995 & January 20, 1996 |
30 | 30 | ||
31 | I. Introduction | 31 | I. Introduction |
32 | 32 | ||
33 | This file describes how to use and modify the PNG reference library | 33 | This file describes how to use and modify the PNG reference library |
34 | (known as libpng) for your own use. There are five sections to this | 34 | (known as libpng) for your own use. There are five sections to this |
35 | file: introduction, structures, reading, writing, and modification and | 35 | file: introduction, structures, reading, writing, and modification and |
36 | configuration notes for various special platforms. In addition to this | 36 | configuration notes for various special platforms. In addition to this |
37 | file, example.c is a good starting point for using the library, as | 37 | file, example.c is a good starting point for using the library, as |
38 | it is heavily commented and should include everything most people | 38 | it is heavily commented and should include everything most people |
39 | will need. We assume that libpng is already installed; see the | 39 | will need. We assume that libpng is already installed; see the |
40 | INSTALL file for instructions on how to install libpng. | 40 | INSTALL file for instructions on how to install libpng. |
41 | 41 | ||
42 | For examples of libpng usage, see the files "example.c", "pngtest.c", | 42 | For examples of libpng usage, see the files "example.c", "pngtest.c", |
43 | and the files in the "contrib" directory, all of which are included in | 43 | and the files in the "contrib" directory, all of which are included in |
44 | the libpng distribution. | 44 | the libpng distribution. |
45 | 45 | ||
46 | Libpng was written as a companion to the PNG specification, as a way | 46 | Libpng was written as a companion to the PNG specification, as a way |
47 | of reducing the amount of time and effort it takes to support the PNG | 47 | of reducing the amount of time and effort it takes to support the PNG |
48 | file format in application programs. | 48 | file format in application programs. |
49 | 49 | ||
50 | The PNG specification (second edition), November 2003, is available as | 50 | The PNG specification (second edition), November 2003, is available as |
51 | a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at | 51 | a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at |
52 | <http://www.w3.org/TR/2003/REC-PNG-20031110/ | 52 | <http://www.w3.org/TR/2003/REC-PNG-20031110/ |
53 | The W3C and ISO documents have identical technical content. | 53 | The W3C and ISO documents have identical technical content. |
54 | 54 | ||
55 | The PNG-1.2 specification is available at | 55 | The PNG-1.2 specification is available at |
56 | <http://www.libpng.org/pub/png/documents/>. It is technically equivalent | 56 | <http://www.libpng.org/pub/png/documents/>. It is technically equivalent |
57 | to the PNG specification (second edition) but has some additional material. | 57 | to the PNG specification (second edition) but has some additional material. |
58 | 58 | ||
59 | The PNG-1.0 specification is available | 59 | The PNG-1.0 specification is available |
60 | as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a | 60 | as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a |
61 | W3C Recommendation <http://www.w3.org/TR/REC.png.html>. | 61 | W3C Recommendation <http://www.w3.org/TR/REC.png.html>. |
62 | 62 | ||
63 | Some additional chunks are described in the special-purpose public chunks | 63 | Some additional chunks are described in the special-purpose public chunks |
64 | documents at <http://www.libpng.org/pub/png/documents/>. | 64 | documents at <http://www.libpng.org/pub/png/documents/>. |
65 | 65 | ||
66 | Other information | 66 | Other information |
67 | about PNG, and the latest version of libpng, can be found at the PNG home | 67 | about PNG, and the latest version of libpng, can be found at the PNG home |
68 | page, <http://www.libpng.org/pub/png/>. | 68 | page, <http://www.libpng.org/pub/png/>. |
69 | 69 | ||
70 | Most users will not have to modify the library significantly; advanced | 70 | Most users will not have to modify the library significantly; advanced |
71 | users may want to modify it more. All attempts were made to make it as | 71 | users may want to modify it more. All attempts were made to make it as |
72 | complete as possible, while keeping the code easy to understand. | 72 | complete as possible, while keeping the code easy to understand. |
73 | Currently, this library only supports C. Support for other languages | 73 | Currently, this library only supports C. Support for other languages |
74 | is being considered. | 74 | is being considered. |
75 | 75 | ||
76 | Libpng has been designed to handle multiple sessions at one time, | 76 | Libpng has been designed to handle multiple sessions at one time, |
77 | to be easily modifiable, to be portable to the vast majority of | 77 | to be easily modifiable, to be portable to the vast majority of |
78 | machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy | 78 | machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy |
79 | to use. The ultimate goal of libpng is to promote the acceptance of | 79 | to use. The ultimate goal of libpng is to promote the acceptance of |
80 | the PNG file format in whatever way possible. While there is still | 80 | the PNG file format in whatever way possible. While there is still |
81 | work to be done (see the TODO file), libpng should cover the | 81 | work to be done (see the TODO file), libpng should cover the |
82 | majority of the needs of its users. | 82 | majority of the needs of its users. |
83 | 83 | ||
84 | Libpng uses zlib for its compression and decompression of PNG files. | 84 | Libpng uses zlib for its compression and decompression of PNG files. |
85 | Further information about zlib, and the latest version of zlib, can | 85 | Further information about zlib, and the latest version of zlib, can |
86 | be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>. | 86 | be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>. |
87 | The zlib compression utility is a general purpose utility that is | 87 | The zlib compression utility is a general purpose utility that is |
88 | useful for more than PNG files, and can be used without libpng. | 88 | useful for more than PNG files, and can be used without libpng. |
89 | See the documentation delivered with zlib for more details. | 89 | See the documentation delivered with zlib for more details. |
90 | You can usually find the source files for the zlib utility wherever you | 90 | You can usually find the source files for the zlib utility wherever you |
91 | find the libpng source files. | 91 | find the libpng source files. |
92 | 92 | ||
93 | Libpng is thread safe, provided the threads are using different | 93 | Libpng is thread safe, provided the threads are using different |
94 | instances of the structures. Each thread should have its own | 94 | instances of the structures. Each thread should have its own |
95 | png_struct and png_info instances, and thus its own image. | 95 | png_struct and png_info instances, and thus its own image. |
96 | Libpng does not protect itself against two threads using the | 96 | Libpng does not protect itself against two threads using the |
97 | same instance of a structure. | 97 | same instance of a structure. |
98 | 98 | ||
99 | II. Structures | 99 | II. Structures |
100 | 100 | ||
101 | There are two main structures that are important to libpng, png_struct | 101 | There are two main structures that are important to libpng, png_struct |
102 | and png_info. Both are internal structures that are no longer exposed | 102 | and png_info. Both are internal structures that are no longer exposed |
103 | in the libpng interface (as of libpng 1.5.0). | 103 | in the libpng interface (as of libpng 1.5.0). |
104 | 104 | ||
105 | The png_info structure is designed to provide information about the | 105 | The png_info structure is designed to provide information about the |
106 | PNG file. At one time, the fields of png_info were intended to be | 106 | PNG file. At one time, the fields of png_info were intended to be |
107 | directly accessible to the user. However, this tended to cause problems | 107 | directly accessible to the user. However, this tended to cause problems |
108 | with applications using dynamically loaded libraries, and as a result | 108 | with applications using dynamically loaded libraries, and as a result |
109 | a set of interface functions for png_info (the png_get_*() and png_set_*() | 109 | a set of interface functions for png_info (the png_get_*() and png_set_*() |
110 | functions) was developed, and direct access to the png_info fields was | 110 | functions) was developed, and direct access to the png_info fields was |
111 | deprecated.. | 111 | deprecated.. |
112 | 112 | ||
113 | The png_struct structure is the object used by the library to decode a | 113 | The png_struct structure is the object used by the library to decode a |
114 | single image. As of 1.5.0 this structure is also not exposed. | 114 | single image. As of 1.5.0 this structure is also not exposed. |
115 | 115 | ||
116 | Almost all libpng APIs require a pointer to a png_struct as the first argument. | 116 | Almost all libpng APIs require a pointer to a png_struct as the first argument. |
117 | Many (in particular the png_set and png_get APIs) also require a pointer | 117 | Many (in particular the png_set and png_get APIs) also require a pointer |
118 | to png_info as the second argument. Some application visible macros | 118 | to png_info as the second argument. Some application visible macros |
119 | defined in png.h designed for basic data access (reading and writing | 119 | defined in png.h designed for basic data access (reading and writing |
120 | integers in the PNG format) don't take a png_info pointer, but it's almost | 120 | integers in the PNG format) don't take a png_info pointer, but it's almost |
121 | always safe to assume that a (png_struct*) has to be passed to call an API | 121 | always safe to assume that a (png_struct*) has to be passed to call an API |
122 | function. | 122 | function. |
123 | 123 | ||
124 | You can have more than one png_info structure associated with an image, | 124 | You can have more than one png_info structure associated with an image, |
125 | as illustrated in pngtest.c, one for information valid prior to the | 125 | as illustrated in pngtest.c, one for information valid prior to the |
126 | IDAT chunks and another (called "end_info" below) for things after them. | 126 | IDAT chunks and another (called "end_info" below) for things after them. |
127 | 127 | ||
128 | The png.h header file is an invaluable reference for programming with libpng. | 128 | The png.h header file is an invaluable reference for programming with libpng. |
129 | And while I'm on the topic, make sure you include the libpng header file: | 129 | And while I'm on the topic, make sure you include the libpng header file: |
130 | 130 | ||
131 | #include <png.h> | 131 | #include <png.h> |
132 | 132 | ||
133 | and also (as of libpng-1.5.0) the zlib header file, if you need it: | 133 | and also (as of libpng-1.5.0) the zlib header file, if you need it: |
134 | 134 | ||
135 | #include <zlib.h> | 135 | #include <zlib.h> |
136 | 136 | ||
137 | Types | 137 | Types |
138 | 138 | ||
139 | The png.h header file defines a number of integral types used by the | 139 | The png.h header file defines a number of integral types used by the |
140 | APIs. Most of these are fairly obvious; for example types corresponding | 140 | APIs. Most of these are fairly obvious; for example types corresponding |
141 | to integers of particular sizes and types for passing color values. | 141 | to integers of particular sizes and types for passing color values. |
142 | 142 | ||
143 | One exception is how non-integral numbers are handled. For application | 143 | One exception is how non-integral numbers are handled. For application |
144 | convenience most APIs that take such numbers have C (double) arguments, | 144 | convenience most APIs that take such numbers have C (double) arguments, |
145 | however internally PNG, and libpng, use 32 bit signed integers and encode | 145 | however internally PNG, and libpng, use 32 bit signed integers and encode |
146 | the value by multiplying by 100,000. As of libpng 1.5.0 a convenience | 146 | the value by multiplying by 100,000. As of libpng 1.5.0 a convenience |
147 | macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point) | 147 | macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point) |
148 | which is simply (png_int_32). | 148 | which is simply (png_int_32). |
149 | 149 | ||
150 | All APIs that take (double) arguments also have a matching API that | 150 | All APIs that take (double) arguments also have a matching API that |
151 | takes the corresponding fixed point integer arguments. The fixed point | 151 | takes the corresponding fixed point integer arguments. The fixed point |
152 | API has the same name as the floating point one with "_fixed" appended. | 152 | API has the same name as the floating point one with "_fixed" appended. |
153 | The actual range of values permitted in the APIs is frequently less than | 153 | The actual range of values permitted in the APIs is frequently less than |
154 | the full range of (png_fixed_point) (-21474 to +21474). When APIs require | 154 | the full range of (png_fixed_point) (-21474 to +21474). When APIs require |
155 | a non-negative argument the type is recorded as png_uint_32 above. Consult | 155 | a non-negative argument the type is recorded as png_uint_32 above. Consult |
156 | the header file and the text below for more information. | 156 | the header file and the text below for more information. |
157 | 157 | ||
158 | Special care must be take with sCAL chunk handling because the chunk itself | 158 | Special care must be take with sCAL chunk handling because the chunk itself |
159 | uses non-integral values encoded as strings containing decimal floating point | 159 | uses non-integral values encoded as strings containing decimal floating point |
160 | numbers. See the comments in the header file. | 160 | numbers. See the comments in the header file. |
161 | 161 | ||
162 | Configuration | 162 | Configuration |
163 | 163 | ||
164 | The main header file function declarations are frequently protected by C | 164 | The main header file function declarations are frequently protected by C |
165 | preprocessing directives of the form: | 165 | preprocessing directives of the form: |
166 | 166 | ||
167 | #ifdef PNG_feature_SUPPORTED | 167 | #ifdef PNG_feature_SUPPORTED |
168 | declare-function | 168 | declare-function |
169 | #endif | 169 | #endif |
170 | ... | 170 | ... |
171 | #ifdef PNG_feature_SUPPORTED | 171 | #ifdef PNG_feature_SUPPORTED |
172 | use-function | 172 | use-function |
173 | #endif | 173 | #endif |
174 | 174 | ||
175 | The library can be built without support for these APIs, although a | 175 | The library can be built without support for these APIs, although a |
176 | standard build will have all implemented APIs. Application programs | 176 | standard build will have all implemented APIs. Application programs |
177 | should check the feature macros before using an API for maximum | 177 | should check the feature macros before using an API for maximum |
178 | portability. From libpng 1.5.0 the feature macros set during the build | 178 | portability. From libpng 1.5.0 the feature macros set during the build |
179 | of libpng are recorded in the header file "pnglibconf.h" and this file | 179 | of libpng are recorded in the header file "pnglibconf.h" and this file |
180 | is always included by png.h. | 180 | is always included by png.h. |
181 | 181 | ||
182 | If you don't need to change the library configuration from the default, skip to | 182 | If you don't need to change the library configuration from the default, skip to |
183 | the next section ("Reading"). | 183 | the next section ("Reading"). |
184 | 184 | ||
185 | Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all | 185 | Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all |
186 | of the build project files in the 'projects' directory simply copy | 186 | of the build project files in the 'projects' directory simply copy |
187 | scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build | 187 | scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build |
188 | systems do not permit easy auto-configuration of the library - they only | 188 | systems do not permit easy auto-configuration of the library - they only |
189 | support the default configuration. | 189 | support the default configuration. |
190 | 190 | ||
191 | The easiest way to make minor changes to the libpng configuration when | 191 | The easiest way to make minor changes to the libpng configuration when |
192 | auto-configuration is supported is to add definitions to the command line | 192 | auto-configuration is supported is to add definitions to the command line |
193 | using (typically) CPPFLAGS. For example: | 193 | using (typically) CPPFLAGS. For example: |
194 | 194 | ||
195 | CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC | 195 | CPPFLAGS=-DPNG_NO_FLOATING_ARITHMETIC |
196 | 196 | ||
197 | will change the internal libpng math implementation for gamma correction and | 197 | will change the internal libpng math implementation for gamma correction and |
198 | other arithmetic calculations to fixed point, avoiding the need for fast | 198 | other arithmetic calculations to fixed point, avoiding the need for fast |
199 | floating point support. The result can be seen in the generated pnglibconf.h - | 199 | floating point support. The result can be seen in the generated pnglibconf.h - |
200 | make sure it contains the changed feature macro setting. | 200 | make sure it contains the changed feature macro setting. |
201 | 201 | ||
202 | If you need to make more extensive configuration changes - more than one or two | 202 | If you need to make more extensive configuration changes - more than one or two |
203 | feature macro settings - you can either add -DPNG_USER_CONFIG to the build | 203 | feature macro settings - you can either add -DPNG_USER_CONFIG to the build |
204 | command line and put a list of feature macro settings in pngusr.h or you can set | 204 | command line and put a list of feature macro settings in pngusr.h or you can set |
205 | DFA_XTRA (a makefile variable) to a file containing the same information in the | 205 | DFA_XTRA (a makefile variable) to a file containing the same information in the |
206 | form of 'option' settings. | 206 | form of 'option' settings. |
207 | 207 | ||
208 | A. Changing pnglibconf.h | 208 | A. Changing pnglibconf.h |
209 | 209 | ||
210 | A variety of methods exist to build libpng. Not all of these support | 210 | A variety of methods exist to build libpng. Not all of these support |
211 | reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be | 211 | reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be |
212 | rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand. | 212 | rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand. |
213 | 213 | ||
214 | Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to | 214 | Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to |
215 | pnglibconf.h and changing the lines defining the supported features, paying | 215 | pnglibconf.h and changing the lines defining the supported features, paying |
216 | very close attention to the 'option' information in scripts/pnglibconf.dfa | 216 | very close attention to the 'option' information in scripts/pnglibconf.dfa |
217 | that describes those features and their requirements. This is easy to get | 217 | that describes those features and their requirements. This is easy to get |
218 | wrong. | 218 | wrong. |
219 | 219 | ||
220 | B. Configuration using DFA_XTRA | 220 | B. Configuration using DFA_XTRA |
221 | 221 | ||
222 | Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later | 222 | Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later |
223 | variant such as 'nawk' or 'gawk', is available. The configure build will | 223 | variant such as 'nawk' or 'gawk', is available. The configure build will |
224 | automatically find an appropriate awk and build pnglibconf.h. | 224 | automatically find an appropriate awk and build pnglibconf.h. |
225 | The scripts/pnglibconf.mak file contains a set of make rules for doing the | 225 | The scripts/pnglibconf.mak file contains a set of make rules for doing the |
226 | same thing if configure is not used, and many of the makefiles in the scripts | 226 | same thing if configure is not used, and many of the makefiles in the scripts |
227 | directory use this approach. | 227 | directory use this approach. |
228 | 228 | ||
229 | When rebuilding simply write a new file containing changed options and set | 229 | When rebuilding simply write a new file containing changed options and set |
230 | DFA_XTRA to the name of this file. This causes the build to append the new file | 230 | DFA_XTRA to the name of this file. This causes the build to append the new file |
231 | to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines | 231 | to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines |
232 | of the following forms: | 232 | of the following forms: |
233 | 233 | ||
234 | everything = off | 234 | everything = off |
235 | 235 | ||
236 | This turns all optional features off. Include it at the start of pngusr.dfa to | 236 | This turns all optional features off. Include it at the start of pngusr.dfa to |
237 | make it easier to build a minimal configuration. You will need to turn at least | 237 | make it easier to build a minimal configuration. You will need to turn at least |
238 | some features on afterward to enable either reading or writing code, or both. | 238 | some features on afterward to enable either reading or writing code, or both. |
239 | 239 | ||
240 | option feature on | 240 | option feature on |
241 | option feature off | 241 | option feature off |
242 | 242 | ||
243 | Enable or disable a single feature. This will automatically enable other | 243 | Enable or disable a single feature. This will automatically enable other |
244 | features required by a feature that is turned on or disable other features that | 244 | features required by a feature that is turned on or disable other features that |
245 | require a feature which is turned off. Conflicting settings will cause an error | 245 | require a feature which is turned off. Conflicting settings will cause an error |
246 | message to be emitted by awk. | 246 | message to be emitted by awk. |
247 | 247 | ||
248 | setting feature default value | 248 | setting feature default value |
249 | 249 | ||
250 | Changes the default value of setting 'feature' to 'value'. There are a small | 250 | Changes the default value of setting 'feature' to 'value'. There are a small |
251 | number of settings listed at the top of pnglibconf.h, they are documented in the | 251 | number of settings listed at the top of pnglibconf.h, they are documented in the |
252 | source code. Most of these values have performance implications for the library | 252 | source code. Most of these values have performance implications for the library |
253 | but most of them have no visible effect on the API. Some can also be overridden | 253 | but most of them have no visible effect on the API. Some can also be overridden |
254 | from the API. | 254 | from the API. |
255 | 255 | ||
256 | This method of building a customized pnglibconf.h is illustrated in | 256 | This method of building a customized pnglibconf.h is illustrated in |
257 | contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and | 257 | contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and |
258 | pngusr.dfa in these directories. | 258 | pngusr.dfa in these directories. |
259 | 259 | ||
260 | C. Configuration using PNG_USR_CONFIG | 260 | C. Configuration using PNG_USR_CONFIG |
261 | 261 | ||
262 | If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file | 262 | If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file |
263 | pngusr.h will automatically be included before the options in | 263 | pngusr.h will automatically be included before the options in |
264 | scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only | 264 | scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only |
265 | macro definitions turning features on or off or setting settings. | 265 | macro definitions turning features on or off or setting settings. |
266 | 266 | ||
267 | Apart from the global setting "everything = off" all the options listed above | 267 | Apart from the global setting "everything = off" all the options listed above |
268 | can be set using macros in pngusr.h: | 268 | can be set using macros in pngusr.h: |
269 | 269 | ||
270 | #define PNG_feature_SUPPORTED | 270 | #define PNG_feature_SUPPORTED |
271 | 271 | ||
272 | is equivalent to: | 272 | is equivalent to: |
273 | 273 | ||
274 | option feature on | 274 | option feature on |
275 | 275 | ||
276 | #define PNG_NO_feature | 276 | #define PNG_NO_feature |
277 | 277 | ||
278 | is equivalent to: | 278 | is equivalent to: |
279 | 279 | ||
280 | option feature off | 280 | option feature off |
281 | 281 | ||
282 | #define PNG_feature value | 282 | #define PNG_feature value |
283 | 283 | ||
284 | is equivalent to: | 284 | is equivalent to: |
285 | 285 | ||
286 | setting feature default value | 286 | setting feature default value |
287 | 287 | ||
288 | Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the | 288 | Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the |
289 | pngusr file you supply override the contents of scripts/pnglibconf.dfa | 289 | pngusr file you supply override the contents of scripts/pnglibconf.dfa |
290 | 290 | ||
291 | If confusing or incomprehensible behavior results it is possible to | 291 | If confusing or incomprehensible behavior results it is possible to |
292 | examine the intermediate file pnglibconf.dfn to find the full set of | 292 | examine the intermediate file pnglibconf.dfn to find the full set of |
293 | dependency information for each setting and option. Simply locate the | 293 | dependency information for each setting and option. Simply locate the |
294 | feature in the file and read the C comments that precede it. | 294 | feature in the file and read the C comments that precede it. |
295 | 295 | ||
296 | This method is also illustrated in the contrib/pngminim/* makefiles and | 296 | This method is also illustrated in the contrib/pngminim/* makefiles and |
297 | pngusr.h. | 297 | pngusr.h. |
298 | 298 | ||
299 | III. Reading | 299 | III. Reading |
300 | 300 | ||
301 | We'll now walk you through the possible functions to call when reading | 301 | We'll now walk you through the possible functions to call when reading |
302 | in a PNG file sequentially, briefly explaining the syntax and purpose | 302 | in a PNG file sequentially, briefly explaining the syntax and purpose |
303 | of each one. See example.c and png.h for more detail. While | 303 | of each one. See example.c and png.h for more detail. While |
304 | progressive reading is covered in the next section, you will still | 304 | progressive reading is covered in the next section, you will still |
305 | need some of the functions discussed in this section to read a PNG | 305 | need some of the functions discussed in this section to read a PNG |
306 | file. | 306 | file. |
307 | 307 | ||
308 | Setup | 308 | Setup |
309 | 309 | ||
310 | You will want to do the I/O initialization(*) before you get into libpng, | 310 | You will want to do the I/O initialization(*) before you get into libpng, |
311 | so if it doesn't work, you don't have much to undo. Of course, you | 311 | so if it doesn't work, you don't have much to undo. Of course, you |
312 | will also want to insure that you are, in fact, dealing with a PNG | 312 | will also want to insure that you are, in fact, dealing with a PNG |
313 | file. Libpng provides a simple check to see if a file is a PNG file. | 313 | file. Libpng provides a simple check to see if a file is a PNG file. |
314 | To use it, pass in the first 1 to 8 bytes of the file to the function | 314 | To use it, pass in the first 1 to 8 bytes of the file to the function |
315 | png_sig_cmp(), and it will return 0 (false) if the bytes match the | 315 | png_sig_cmp(), and it will return 0 (false) if the bytes match the |
316 | corresponding bytes of the PNG signature, or nonzero (true) otherwise. | 316 | corresponding bytes of the PNG signature, or nonzero (true) otherwise. |
317 | Of course, the more bytes you pass in, the greater the accuracy of the | 317 | Of course, the more bytes you pass in, the greater the accuracy of the |
318 | prediction. | 318 | prediction. |
319 | 319 | ||
320 | If you are intending to keep the file pointer open for use in libpng, | 320 | If you are intending to keep the file pointer open for use in libpng, |
321 | you must ensure you don't read more than 8 bytes from the beginning | 321 | you must ensure you don't read more than 8 bytes from the beginning |
322 | of the file, and you also have to make a call to png_set_sig_bytes_read() | 322 | of the file, and you also have to make a call to png_set_sig_bytes_read() |
323 | with the number of bytes you read from the beginning. Libpng will | 323 | with the number of bytes you read from the beginning. Libpng will |
324 | then only check the bytes (if any) that your program didn't read. | 324 | then only check the bytes (if any) that your program didn't read. |
325 | 325 | ||
326 | (*): If you are not using the standard I/O functions, you will need | 326 | (*): If you are not using the standard I/O functions, you will need |
327 | to replace them with custom functions. See the discussion under | 327 | to replace them with custom functions. See the discussion under |
328 | Customizing libpng. | 328 | Customizing libpng. |
329 | 329 | ||
330 | 330 | ||
331 | FILE *fp = fopen(file_name, "rb"); | 331 | FILE *fp = fopen(file_name, "rb"); |
332 | if (!fp) | 332 | if (!fp) |
333 | { | 333 | { |
334 | return (ERROR); | 334 | return (ERROR); |
335 | } | 335 | } |
336 | 336 | ||
337 | fread(header, 1, number, fp); | 337 | fread(header, 1, number, fp); |
338 | is_png = !png_sig_cmp(header, 0, number); | 338 | is_png = !png_sig_cmp(header, 0, number); |
339 | 339 | ||
340 | if (!is_png) | 340 | if (!is_png) |
341 | { | 341 | { |
342 | return (NOT_PNG); | 342 | return (NOT_PNG); |
343 | } | 343 | } |
344 | 344 | ||
345 | 345 | ||
346 | Next, png_struct and png_info need to be allocated and initialized. In | 346 | Next, png_struct and png_info need to be allocated and initialized. In |
347 | order to ensure that the size of these structures is correct even with a | 347 | order to ensure that the size of these structures is correct even with a |
348 | dynamically linked libpng, there are functions to initialize and | 348 | dynamically linked libpng, there are functions to initialize and |
349 | allocate the structures. We also pass the library version, optional | 349 | allocate the structures. We also pass the library version, optional |
350 | pointers to error handling functions, and a pointer to a data struct for | 350 | pointers to error handling functions, and a pointer to a data struct for |
351 | use by the error functions, if necessary (the pointer and functions can | 351 | use by the error functions, if necessary (the pointer and functions can |
352 | be NULL if the default error handlers are to be used). See the section | 352 | be NULL if the default error handlers are to be used). See the section |
353 | on Changes to Libpng below regarding the old initialization functions. | 353 | on Changes to Libpng below regarding the old initialization functions. |
354 | The structure allocation functions quietly return NULL if they fail to | 354 | The structure allocation functions quietly return NULL if they fail to |
355 | create the structure, so your application should check for that. | 355 | create the structure, so your application should check for that. |
356 | 356 | ||
357 | png_structp png_ptr = png_create_read_struct | 357 | png_structp png_ptr = png_create_read_struct |
358 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | 358 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, |
359 | user_error_fn, user_warning_fn); | 359 | user_error_fn, user_warning_fn); |
360 | 360 | ||
361 | if (!png_ptr) | 361 | if (!png_ptr) |
362 | return (ERROR); | 362 | return (ERROR); |
363 | 363 | ||
364 | png_infop info_ptr = png_create_info_struct(png_ptr); | 364 | png_infop info_ptr = png_create_info_struct(png_ptr); |
365 | 365 | ||
366 | if (!info_ptr) | 366 | if (!info_ptr) |
367 | { | 367 | { |
368 | png_destroy_read_struct(&png_ptr, | 368 | png_destroy_read_struct(&png_ptr, |
369 | (png_infopp)NULL, (png_infopp)NULL); | 369 | (png_infopp)NULL, (png_infopp)NULL); |
370 | return (ERROR); | 370 | return (ERROR); |
371 | } | 371 | } |
372 | 372 | ||
373 | If you want to use your own memory allocation routines, | 373 | If you want to use your own memory allocation routines, |
374 | use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use | 374 | use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use |
375 | png_create_read_struct_2() instead of png_create_read_struct(): | 375 | png_create_read_struct_2() instead of png_create_read_struct(): |
376 | 376 | ||
377 | png_structp png_ptr = png_create_read_struct_2 | 377 | png_structp png_ptr = png_create_read_struct_2 |
378 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | 378 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, |
379 | user_error_fn, user_warning_fn, (png_voidp) | 379 | user_error_fn, user_warning_fn, (png_voidp) |
380 | user_mem_ptr, user_malloc_fn, user_free_fn); | 380 | user_mem_ptr, user_malloc_fn, user_free_fn); |
381 | 381 | ||
382 | The error handling routines passed to png_create_read_struct() | 382 | The error handling routines passed to png_create_read_struct() |
383 | and the memory alloc/free routines passed to png_create_struct_2() | 383 | and the memory alloc/free routines passed to png_create_struct_2() |
384 | are only necessary if you are not using the libpng supplied error | 384 | are only necessary if you are not using the libpng supplied error |
385 | handling and memory alloc/free functions. | 385 | handling and memory alloc/free functions. |
386 | 386 | ||
387 | When libpng encounters an error, it expects to longjmp back | 387 | When libpng encounters an error, it expects to longjmp back |
388 | to your routine. Therefore, you will need to call setjmp and pass | 388 | to your routine. Therefore, you will need to call setjmp and pass |
389 | your png_jmpbuf(png_ptr). If you read the file from different | 389 | your png_jmpbuf(png_ptr). If you read the file from different |
390 | routines, you will need to update the longjmp buffer every time you enter | 390 | routines, you will need to update the longjmp buffer every time you enter |
391 | a new routine that will call a png_*() function. | 391 | a new routine that will call a png_*() function. |
392 | 392 | ||
393 | See your documentation of setjmp/longjmp for your compiler for more | 393 | See your documentation of setjmp/longjmp for your compiler for more |
394 | information on setjmp/longjmp. See the discussion on libpng error | 394 | information on setjmp/longjmp. See the discussion on libpng error |
395 | handling in the Customizing Libpng section below for more information | 395 | handling in the Customizing Libpng section below for more information |
396 | on the libpng error handling. If an error occurs, and libpng longjmp's | 396 | on the libpng error handling. If an error occurs, and libpng longjmp's |
397 | back to your setjmp, you will want to call png_destroy_read_struct() to | 397 | back to your setjmp, you will want to call png_destroy_read_struct() to |
398 | free any memory. | 398 | free any memory. |
399 | 399 | ||
400 | if (setjmp(png_jmpbuf(png_ptr))) | 400 | if (setjmp(png_jmpbuf(png_ptr))) |
401 | { | 401 | { |
402 | png_destroy_read_struct(&png_ptr, &info_ptr, | 402 | png_destroy_read_struct(&png_ptr, &info_ptr, |
403 | &end_info); | 403 | &end_info); |
404 | fclose(fp); | 404 | fclose(fp); |
405 | return (ERROR); | 405 | return (ERROR); |
406 | } | 406 | } |
407 | 407 | ||
408 | Pass (png_infopp)NULL instead of &end_info if you didn't create | 408 | Pass (png_infopp)NULL instead of &end_info if you didn't create |
409 | an end_info structure. | 409 | an end_info structure. |
410 | 410 | ||
411 | If you would rather avoid the complexity of setjmp/longjmp issues, | 411 | If you would rather avoid the complexity of setjmp/longjmp issues, |
412 | you can compile libpng with PNG_NO_SETJMP, in which case | 412 | you can compile libpng with PNG_NO_SETJMP, in which case |
413 | errors will result in a call to PNG_ABORT() which defaults to abort(). | 413 | errors will result in a call to PNG_ABORT() which defaults to abort(). |
414 | 414 | ||
415 | You can #define PNG_ABORT() to a function that does something | 415 | You can #define PNG_ABORT() to a function that does something |
416 | more useful than abort(), as long as your function does not | 416 | more useful than abort(), as long as your function does not |
417 | return. | 417 | return. |
418 | 418 | ||
419 | Now you need to set up the input code. The default for libpng is to | 419 | Now you need to set up the input code. The default for libpng is to |
420 | use the C function fread(). If you use this, you will need to pass a | 420 | use the C function fread(). If you use this, you will need to pass a |
421 | valid FILE * in the function png_init_io(). Be sure that the file is | 421 | valid FILE * in the function png_init_io(). Be sure that the file is |
422 | opened in binary mode. If you wish to handle reading data in another | 422 | opened in binary mode. If you wish to handle reading data in another |
423 | way, you need not call the png_init_io() function, but you must then | 423 | way, you need not call the png_init_io() function, but you must then |
424 | implement the libpng I/O methods discussed in the Customizing Libpng | 424 | implement the libpng I/O methods discussed in the Customizing Libpng |
425 | section below. | 425 | section below. |
426 | 426 | ||
427 | png_init_io(png_ptr, fp); | 427 | png_init_io(png_ptr, fp); |
428 | 428 | ||
429 | If you had previously opened the file and read any of the signature from | 429 | If you had previously opened the file and read any of the signature from |
430 | the beginning in order to see if this was a PNG file, you need to let | 430 | the beginning in order to see if this was a PNG file, you need to let |
431 | libpng know that there are some bytes missing from the start of the file. | 431 | libpng know that there are some bytes missing from the start of the file. |
432 | 432 | ||
433 | png_set_sig_bytes(png_ptr, number); | 433 | png_set_sig_bytes(png_ptr, number); |
434 | 434 | ||
435 | You can change the zlib compression buffer size to be used while | 435 | You can change the zlib compression buffer size to be used while |
436 | reading compressed data with | 436 | reading compressed data with |
437 | 437 | ||
438 | png_set_compression_buffer_size(png_ptr, buffer_size); | 438 | png_set_compression_buffer_size(png_ptr, buffer_size); |
439 | 439 | ||
440 | where the default size is 8192 bytes. Note that the buffer size | 440 | where the default size is 8192 bytes. Note that the buffer size |
441 | is changed immediately and the buffer is reallocated immediately, | 441 | is changed immediately and the buffer is reallocated immediately, |
442 | instead of setting a flag to be acted upon later. | 442 | instead of setting a flag to be acted upon later. |
443 | 443 | ||
444 | If you want CRC errors to be handled in a different manner than | 444 | If you want CRC errors to be handled in a different manner than |
445 | the default, use | 445 | the default, use |
446 | 446 | ||
447 | png_set_crc_action(png_ptr, crit_action, ancil_action); | 447 | png_set_crc_action(png_ptr, crit_action, ancil_action); |
448 | 448 | ||
449 | The values for png_set_crc_action() say how libpng is to handle CRC errors in | 449 | The values for png_set_crc_action() say how libpng is to handle CRC errors in |
450 | ancillary and critical chunks, and whether to use the data contained | 450 | ancillary and critical chunks, and whether to use the data contained |
451 | therein. Note that it is impossible to "discard" data in a critical | 451 | therein. Note that it is impossible to "discard" data in a critical |
452 | chunk. | 452 | chunk. |
453 | 453 | ||
454 | Choices for (int) crit_action are | 454 | Choices for (int) crit_action are |
455 | PNG_CRC_DEFAULT 0 error/quit | 455 | PNG_CRC_DEFAULT 0 error/quit |
456 | PNG_CRC_ERROR_QUIT 1 error/quit | 456 | PNG_CRC_ERROR_QUIT 1 error/quit |
457 | PNG_CRC_WARN_USE 3 warn/use data | 457 | PNG_CRC_WARN_USE 3 warn/use data |
458 | PNG_CRC_QUIET_USE 4 quiet/use data | 458 | PNG_CRC_QUIET_USE 4 quiet/use data |
459 | PNG_CRC_NO_CHANGE 5 use the current value | 459 | PNG_CRC_NO_CHANGE 5 use the current value |
460 | 460 | ||
461 | Choices for (int) ancil_action are | 461 | Choices for (int) ancil_action are |
462 | PNG_CRC_DEFAULT 0 error/quit | 462 | PNG_CRC_DEFAULT 0 error/quit |
463 | PNG_CRC_ERROR_QUIT 1 error/quit | 463 | PNG_CRC_ERROR_QUIT 1 error/quit |
464 | PNG_CRC_WARN_DISCARD 2 warn/discard data | 464 | PNG_CRC_WARN_DISCARD 2 warn/discard data |
465 | PNG_CRC_WARN_USE 3 warn/use data | 465 | PNG_CRC_WARN_USE 3 warn/use data |
466 | PNG_CRC_QUIET_USE 4 quiet/use data | 466 | PNG_CRC_QUIET_USE 4 quiet/use data |
467 | PNG_CRC_NO_CHANGE 5 use the current value | 467 | PNG_CRC_NO_CHANGE 5 use the current value |
468 | 468 | ||
469 | Setting up callback code | 469 | Setting up callback code |
470 | 470 | ||
471 | You can set up a callback function to handle any unknown chunks in the | 471 | You can set up a callback function to handle any unknown chunks in the |
472 | input stream. You must supply the function | 472 | input stream. You must supply the function |
473 | 473 | ||
474 | read_chunk_callback(png_structp png_ptr, | 474 | read_chunk_callback(png_structp png_ptr, |
475 | png_unknown_chunkp chunk); | 475 | png_unknown_chunkp chunk); |
476 | { | 476 | { |
477 | /* The unknown chunk structure contains your | 477 | /* The unknown chunk structure contains your |
478 | chunk data, along with similar data for any other | 478 | chunk data, along with similar data for any other |
479 | unknown chunks: */ | 479 | unknown chunks: */ |
480 | 480 | ||
481 | png_byte name[5]; | 481 | png_byte name[5]; |
482 | png_byte *data; | 482 | png_byte *data; |
483 | png_size_t size; | 483 | png_size_t size; |
484 | 484 | ||
485 | /* Note that libpng has already taken care of | 485 | /* Note that libpng has already taken care of |
486 | the CRC handling */ | 486 | the CRC handling */ |
487 | 487 | ||
488 | /* put your code here. Search for your chunk in the | 488 | /* put your code here. Search for your chunk in the |
489 | unknown chunk structure, process it, and return one | 489 | unknown chunk structure, process it, and return one |
490 | of the following: */ | 490 | of the following: */ |
491 | 491 | ||
492 | return (-n); /* chunk had an error */ | 492 | return (-n); /* chunk had an error */ |
493 | return (0); /* did not recognize */ | 493 | return (0); /* did not recognize */ |
494 | return (n); /* success */ | 494 | return (n); /* success */ |
495 | } | 495 | } |
496 | 496 | ||
497 | (You can give your function another name that you like instead of | 497 | (You can give your function another name that you like instead of |
498 | "read_chunk_callback") | 498 | "read_chunk_callback") |
499 | 499 | ||
500 | To inform libpng about your function, use | 500 | To inform libpng about your function, use |
501 | 501 | ||
502 | png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr, | 502 | png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr, |
503 | read_chunk_callback); | 503 | read_chunk_callback); |
504 | 504 | ||
505 | This names not only the callback function, but also a user pointer that | 505 | This names not only the callback function, but also a user pointer that |
506 | you can retrieve with | 506 | you can retrieve with |
507 | 507 | ||
508 | png_get_user_chunk_ptr(png_ptr); | 508 | png_get_user_chunk_ptr(png_ptr); |
509 | 509 | ||
510 | If you call the png_set_read_user_chunk_fn() function, then all unknown | 510 | If you call the png_set_read_user_chunk_fn() function, then all unknown |
511 | chunks will be saved when read, in case your callback function will need | 511 | chunks will be saved when read, in case your callback function will need |
512 | one or more of them. This behavior can be changed with the | 512 | one or more of them. This behavior can be changed with the |
513 | png_set_keep_unknown_chunks() function, described below. | 513 | png_set_keep_unknown_chunks() function, described below. |
514 | 514 | ||
515 | At this point, you can set up a callback function that will be | 515 | At this point, you can set up a callback function that will be |
516 | called after each row has been read, which you can use to control | 516 | called after each row has been read, which you can use to control |
517 | a progress meter or the like. It's demonstrated in pngtest.c. | 517 | a progress meter or the like. It's demonstrated in pngtest.c. |
518 | You must supply a function | 518 | You must supply a function |
519 | 519 | ||
520 | void read_row_callback(png_structp png_ptr, | 520 | void read_row_callback(png_structp png_ptr, |
521 | png_uint_32 row, int pass); | 521 | png_uint_32 row, int pass); |
522 | { | 522 | { |
523 | /* put your code here */ | 523 | /* put your code here */ |
524 | } | 524 | } |
525 | 525 | ||
526 | (You can give it another name that you like instead of "read_row_callback") | 526 | (You can give it another name that you like instead of "read_row_callback") |
527 | 527 | ||
528 | To inform libpng about your function, use | 528 | To inform libpng about your function, use |
529 | 529 | ||
530 | png_set_read_status_fn(png_ptr, read_row_callback); | 530 | png_set_read_status_fn(png_ptr, read_row_callback); |
531 | 531 | ||
532 | When this function is called the row has already been completely processed and | 532 | When this function is called the row has already been completely processed and |
533 | the 'row' and 'pass' refer to the next row to be handled. For the | 533 | the 'row' and 'pass' refer to the next row to be handled. For the |
534 | non-interlaced case the row that was just handled is simply one less than the | 534 | non-interlaced case the row that was just handled is simply one less than the |
535 | passed in row number, and pass will always be 0. For the interlaced case the | 535 | passed in row number, and pass will always be 0. For the interlaced case the |
536 | same applies unless the row value is 0, in which case the row just handled was | 536 | same applies unless the row value is 0, in which case the row just handled was |
537 | the last one from one of the preceding passes. Because interlacing may skip a | 537 | the last one from one of the preceding passes. Because interlacing may skip a |
538 | pass you cannot be sure that the preceding pass is just 'pass-1', if you really | 538 | pass you cannot be sure that the preceding pass is just 'pass-1', if you really |
539 | need to know what the last pass is record (row,pass) from the callback and use | 539 | need to know what the last pass is record (row,pass) from the callback and use |
540 | the last recorded value each time. | 540 | the last recorded value each time. |
541 | 541 | ||
542 | As with the user transform you can find the output row using the | 542 | As with the user transform you can find the output row using the |
543 | PNG_ROW_FROM_PASS_ROW macro. | 543 | PNG_ROW_FROM_PASS_ROW macro. |
544 | 544 | ||
545 | Unknown-chunk handling | 545 | Unknown-chunk handling |
546 | 546 | ||
547 | Now you get to set the way the library processes unknown chunks in the | 547 | Now you get to set the way the library processes unknown chunks in the |
548 | input PNG stream. Both known and unknown chunks will be read. Normal | 548 | input PNG stream. Both known and unknown chunks will be read. Normal |
549 | behavior is that known chunks will be parsed into information in | 549 | behavior is that known chunks will be parsed into information in |
550 | various info_ptr members while unknown chunks will be discarded. This | 550 | various info_ptr members while unknown chunks will be discarded. This |
551 | behavior can be wasteful if your application will never use some known | 551 | behavior can be wasteful if your application will never use some known |
552 | chunk types. To change this, you can call: | 552 | chunk types. To change this, you can call: |
553 | 553 | ||
554 | png_set_keep_unknown_chunks(png_ptr, keep, | 554 | png_set_keep_unknown_chunks(png_ptr, keep, |
555 | chunk_list, num_chunks); | 555 | chunk_list, num_chunks); |
556 | keep - 0: default unknown chunk handling | 556 | keep - 0: default unknown chunk handling |
557 | 1: ignore; do not keep | 557 | 1: ignore; do not keep |
558 | 2: keep only if safe-to-copy | 558 | 2: keep only if safe-to-copy |
559 | 3: keep even if unsafe-to-copy | 559 | 3: keep even if unsafe-to-copy |
560 | 560 | ||
561 | You can use these definitions: | 561 | You can use these definitions: |
562 | PNG_HANDLE_CHUNK_AS_DEFAULT 0 | 562 | PNG_HANDLE_CHUNK_AS_DEFAULT 0 |
563 | PNG_HANDLE_CHUNK_NEVER 1 | 563 | PNG_HANDLE_CHUNK_NEVER 1 |
564 | PNG_HANDLE_CHUNK_IF_SAFE 2 | 564 | PNG_HANDLE_CHUNK_IF_SAFE 2 |
565 | PNG_HANDLE_CHUNK_ALWAYS 3 | 565 | PNG_HANDLE_CHUNK_ALWAYS 3 |
566 | 566 | ||
567 | chunk_list - list of chunks affected (a byte string, | 567 | chunk_list - list of chunks affected (a byte string, |
568 | five bytes per chunk, NULL or '\0' if | 568 | five bytes per chunk, NULL or '\0' if |
569 | num_chunks is 0) | 569 | num_chunks is 0) |
570 | 570 | ||
571 | num_chunks - number of chunks affected; if 0, all | 571 | num_chunks - number of chunks affected; if 0, all |
572 | unknown chunks are affected. If nonzero, | 572 | unknown chunks are affected. If nonzero, |
573 | only the chunks in the list are affected | 573 | only the chunks in the list are affected |
574 | 574 | ||
575 | Unknown chunks declared in this way will be saved as raw data onto a | 575 | Unknown chunks declared in this way will be saved as raw data onto a |
576 | list of png_unknown_chunk structures. If a chunk that is normally | 576 | list of png_unknown_chunk structures. If a chunk that is normally |
577 | known to libpng is named in the list, it will be handled as unknown, | 577 | known to libpng is named in the list, it will be handled as unknown, |
578 | according to the "keep" directive. If a chunk is named in successive | 578 | according to the "keep" directive. If a chunk is named in successive |
579 | instances of png_set_keep_unknown_chunks(), the final instance will | 579 | instances of png_set_keep_unknown_chunks(), the final instance will |
580 | take precedence. The IHDR and IEND chunks should not be named in | 580 | take precedence. The IHDR and IEND chunks should not be named in |
581 | chunk_list; if they are, libpng will process them normally anyway. | 581 | chunk_list; if they are, libpng will process them normally anyway. |
582 | If you know that your application will never make use of some particular | 582 | If you know that your application will never make use of some particular |
583 | chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below. | 583 | chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below. |
584 | 584 | ||
585 | Here is an example of the usage of png_set_keep_unknown_chunks(), | 585 | Here is an example of the usage of png_set_keep_unknown_chunks(), |
586 | where the private "vpAg" chunk will later be processed by a user chunk | 586 | where the private "vpAg" chunk will later be processed by a user chunk |
587 | callback function: | 587 | callback function: |
588 | 588 | ||
589 | png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'}; | 589 | png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'}; |
590 | 590 | ||
591 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) | 591 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) |
592 | png_byte unused_chunks[]= | 592 | png_byte unused_chunks[]= |
593 | { | 593 | { |
594 | 104, 73, 83, 84, (png_byte) '\0', /* hIST */ | 594 | 104, 73, 83, 84, (png_byte) '\0', /* hIST */ |
595 | 105, 84, 88, 116, (png_byte) '\0', /* iTXt */ | 595 | 105, 84, 88, 116, (png_byte) '\0', /* iTXt */ |
596 | 112, 67, 65, 76, (png_byte) '\0', /* pCAL */ | 596 | 112, 67, 65, 76, (png_byte) '\0', /* pCAL */ |
597 | 115, 67, 65, 76, (png_byte) '\0', /* sCAL */ | 597 | 115, 67, 65, 76, (png_byte) '\0', /* sCAL */ |
598 | 115, 80, 76, 84, (png_byte) '\0', /* sPLT */ | 598 | 115, 80, 76, 84, (png_byte) '\0', /* sPLT */ |
599 | 116, 73, 77, 69, (png_byte) '\0', /* tIME */ | 599 | 116, 73, 77, 69, (png_byte) '\0', /* tIME */ |
600 | }; | 600 | }; |
601 | #endif | 601 | #endif |
602 | 602 | ||
603 | ... | 603 | ... |
604 | 604 | ||
605 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) | 605 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED) |
606 | /* ignore all unknown chunks: */ | 606 | /* ignore all unknown chunks: */ |
607 | png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0); | 607 | png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0); |
608 | 608 | ||
609 | /* except for vpAg: */ | 609 | /* except for vpAg: */ |
610 | png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1); | 610 | png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1); |
611 | 611 | ||
612 | /* also ignore unused known chunks: */ | 612 | /* also ignore unused known chunks: */ |
613 | png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks, | 613 | png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks, |
614 | (int)sizeof(unused_chunks)/5); | 614 | (int)sizeof(unused_chunks)/5); |
615 | #endif | 615 | #endif |
616 | 616 | ||
617 | User limits | 617 | User limits |
618 | 618 | ||
619 | The PNG specification allows the width and height of an image to be as | 619 | The PNG specification allows the width and height of an image to be as |
620 | large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns. | 620 | large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns. |
621 | Since very few applications really need to process such large images, | 621 | Since very few applications really need to process such large images, |
622 | we have imposed an arbitrary 1-million limit on rows and columns. | 622 | we have imposed an arbitrary 1-million limit on rows and columns. |
623 | Larger images will be rejected immediately with a png_error() call. If | 623 | Larger images will be rejected immediately with a png_error() call. If |
624 | you wish to change this limit, you can use | 624 | you wish to change this limit, you can use |
625 | 625 | ||
626 | png_set_user_limits(png_ptr, width_max, height_max); | 626 | png_set_user_limits(png_ptr, width_max, height_max); |
627 | 627 | ||
628 | to set your own limits, or use width_max = height_max = 0x7fffffffL | 628 | to set your own limits, or use width_max = height_max = 0x7fffffffL |
629 | to allow all valid dimensions (libpng may reject some very large images | 629 | to allow all valid dimensions (libpng may reject some very large images |
630 | anyway because of potential buffer overflow conditions). | 630 | anyway because of potential buffer overflow conditions). |
631 | 631 | ||
632 | You should put this statement after you create the PNG structure and | 632 | You should put this statement after you create the PNG structure and |
633 | before calling png_read_info(), png_read_png(), or png_process_data(). | 633 | before calling png_read_info(), png_read_png(), or png_process_data(). |
634 | 634 | ||
635 | When writing a PNG datastream, put this statement before calling | 635 | When writing a PNG datastream, put this statement before calling |
636 | png_write_info() or png_write_png(). | 636 | png_write_info() or png_write_png(). |
637 | 637 | ||
638 | If you need to retrieve the limits that are being applied, use | 638 | If you need to retrieve the limits that are being applied, use |
639 | 639 | ||
640 | width_max = png_get_user_width_max(png_ptr); | 640 | width_max = png_get_user_width_max(png_ptr); |
641 | height_max = png_get_user_height_max(png_ptr); | 641 | height_max = png_get_user_height_max(png_ptr); |
642 | 642 | ||
643 | The PNG specification sets no limit on the number of ancillary chunks | 643 | The PNG specification sets no limit on the number of ancillary chunks |
644 | allowed in a PNG datastream. You can impose a limit on the total number | 644 | allowed in a PNG datastream. You can impose a limit on the total number |
645 | of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with | 645 | of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with |
646 | 646 | ||
647 | png_set_chunk_cache_max(png_ptr, user_chunk_cache_max); | 647 | png_set_chunk_cache_max(png_ptr, user_chunk_cache_max); |
648 | 648 | ||
649 | where 0x7fffffffL means unlimited. You can retrieve this limit with | 649 | where 0x7fffffffL means unlimited. You can retrieve this limit with |
650 | 650 | ||
651 | chunk_cache_max = png_get_chunk_cache_max(png_ptr); | 651 | chunk_cache_max = png_get_chunk_cache_max(png_ptr); |
652 | 652 | ||
653 | This limit also applies to the number of buffers that can be allocated | 653 | This limit also applies to the number of buffers that can be allocated |
654 | by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks. | 654 | by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks. |
655 | 655 | ||
656 | You can also set a limit on the amount of memory that a compressed chunk | 656 | You can also set a limit on the amount of memory that a compressed chunk |
657 | other than IDAT can occupy, with | 657 | other than IDAT can occupy, with |
658 | 658 | ||
659 | png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max); | 659 | png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max); |
660 | 660 | ||
661 | and you can retrieve the limit with | 661 | and you can retrieve the limit with |
662 | 662 | ||
663 | chunk_malloc_max = png_get_chunk_malloc_max(png_ptr); | 663 | chunk_malloc_max = png_get_chunk_malloc_max(png_ptr); |
664 | 664 | ||
665 | Any chunks that would cause either of these limits to be exceeded will | 665 | Any chunks that would cause either of these limits to be exceeded will |
666 | be ignored. | 666 | be ignored. |
667 | 667 | ||
668 | Information about your system | 668 | Information about your system |
669 | 669 | ||
670 | If you intend to display the PNG or to incorporate it in other image data you | 670 | If you intend to display the PNG or to incorporate it in other image data you |
671 | need to tell libpng information about your display or drawing surface so that | 671 | need to tell libpng information about your display or drawing surface so that |
672 | libpng can convert the values in the image to match the display. | 672 | libpng can convert the values in the image to match the display. |
673 | 673 | ||
674 | From libpng-1.5.4 this information can be set before reading the PNG file | 674 | From libpng-1.5.4 this information can be set before reading the PNG file |
675 | header. In earlier versions png_set_gamma() existed but behaved incorrectly if | 675 | header. In earlier versions png_set_gamma() existed but behaved incorrectly if |
676 | called before the PNG file header had been read and png_set_alpha_mode() did not | 676 | called before the PNG file header had been read and png_set_alpha_mode() did not |
677 | exist. | 677 | exist. |
678 | 678 | ||
679 | If you need to support versions prior to libpng-1.5.4 test the version number | 679 | If you need to support versions prior to libpng-1.5.4 test the version number |
680 | as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures | 680 | as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures |
681 | described in the appropriate manual page. | 681 | described in the appropriate manual page. |
682 | 682 | ||
683 | You give libpng the encoding expected by your system expressed as a 'gamma' | 683 | You give libpng the encoding expected by your system expressed as a 'gamma' |
684 | value. You can also specify a default encoding for the PNG file in | 684 | value. You can also specify a default encoding for the PNG file in |
685 | case the required information is missing from the file. By default libpng | 685 | case the required information is missing from the file. By default libpng |
686 | assumes that the PNG data matches your system, to keep this default call: | 686 | assumes that the PNG data matches your system, to keep this default call: |
687 | 687 | ||
688 | png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/); | 688 | png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/); |
689 | 689 | ||
690 | or you can use the fixed point equivalent: | 690 | or you can use the fixed point equivalent: |
691 | 691 | ||
692 | png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma); | 692 | png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma, PNG_FP_1/screen_gamma); |
693 | 693 | ||
694 | If you don't know the gamma for your system it is probably 2.2 - a good | 694 | If you don't know the gamma for your system it is probably 2.2 - a good |
695 | approximation to the IEC standard for display systems (sRGB). If images are | 695 | approximation to the IEC standard for display systems (sRGB). If images are |
696 | too contrasty or washed out you got the value wrong - check your system | 696 | too contrasty or washed out you got the value wrong - check your system |
697 | documentation! | 697 | documentation! |
698 | 698 | ||
699 | Many systems permit the system gamma to be changed via a lookup table in the | 699 | Many systems permit the system gamma to be changed via a lookup table in the |
700 | display driver, a few systems, including older Macs, change the response by | 700 | display driver, a few systems, including older Macs, change the response by |
701 | default. As of 1.5.4 three special values are available to handle common | 701 | default. As of 1.5.4 three special values are available to handle common |
702 | situations: | 702 | situations: |
703 | 703 | ||
704 | PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1 | 704 | PNG_DEFAULT_sRGB: Indicates that the system conforms to the IEC 61966-2-1 |
705 | standard. This matches almost all systems. | 705 | standard. This matches almost all systems. |
706 | PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6) | 706 | PNG_GAMMA_MAC_18: Indicates that the system is an older (pre Mac OS 10.6) |
707 | Apple Macintosh system with the default settings. | 707 | Apple Macintosh system with the default settings. |
708 | PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the | 708 | PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates that the |
709 | system expects data with no gamma encoding. | 709 | system expects data with no gamma encoding. |
710 | 710 | ||
711 | You would use the linear (unencoded) value if you need to process the pixel | 711 | You would use the linear (unencoded) value if you need to process the pixel |
712 | values further because this avoids the need to decode and reencode each | 712 | values further because this avoids the need to decode and reencode each |
713 | component value whenever arithmetic is performed. A lot of graphics software | 713 | component value whenever arithmetic is performed. A lot of graphics software |
714 | uses linear values for this reason, often with higher precision component values | 714 | uses linear values for this reason, often with higher precision component values |
715 | to preserve overall accuracy. | 715 | to preserve overall accuracy. |
716 | 716 | ||
717 | The second thing you may need to tell libpng about is how your system handles | 717 | The second thing you may need to tell libpng about is how your system handles |
718 | alpha channel information. Some, but not all, PNG files contain an alpha | 718 | alpha channel information. Some, but not all, PNG files contain an alpha |
719 | channel. To display these files correctly you need to compose the data onto a | 719 | channel. To display these files correctly you need to compose the data onto a |
720 | suitable background, as described in the PNG specification. | 720 | suitable background, as described in the PNG specification. |
721 | 721 | ||
722 | Libpng only supports composing onto a single color (using png_set_background; | 722 | Libpng only supports composing onto a single color (using png_set_background; |
723 | see below). Otherwise you must do the composition yourself and, in this case, | 723 | see below). Otherwise you must do the composition yourself and, in this case, |
724 | you may need to call png_set_alpha_mode: | 724 | you may need to call png_set_alpha_mode: |
725 | 725 | ||
726 | #if PNG_LIBPNG_VER >= 10504 | 726 | #if PNG_LIBPNG_VER >= 10504 |
727 | png_set_alpha_mode(png_ptr, mode, screen_gamma); | 727 | png_set_alpha_mode(png_ptr, mode, screen_gamma); |
728 | #else | 728 | #else |
729 | png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma); | 729 | png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma); |
730 | #endif | 730 | #endif |
731 | 731 | ||
732 | The screen_gamma value is the same as the argument to png_set_gamma; however, | 732 | The screen_gamma value is the same as the argument to png_set_gamma; however, |
733 | how it affects the output depends on the mode. png_set_alpha_mode() sets the | 733 | how it affects the output depends on the mode. png_set_alpha_mode() sets the |
734 | file gamma default to 1/screen_gamma, so normally you don't need to call | 734 | file gamma default to 1/screen_gamma, so normally you don't need to call |
735 | png_set_gamma. If you need different defaults call png_set_gamma() before | 735 | png_set_gamma. If you need different defaults call png_set_gamma() before |
736 | png_set_alpha_mode() - if you call it after it will override the settings made | 736 | png_set_alpha_mode() - if you call it after it will override the settings made |
737 | by png_set_alpha_mode(). | 737 | by png_set_alpha_mode(). |
738 | 738 | ||
739 | The mode is as follows: | 739 | The mode is as follows: |
740 | 740 | ||
741 | PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red, | 741 | PNG_ALPHA_PNG: The data is encoded according to the PNG specification. Red, |
742 | green and blue, or gray, components are gamma encoded color | 742 | green and blue, or gray, components are gamma encoded color |
743 | values and are not premultiplied by the alpha value. The | 743 | values and are not premultiplied by the alpha value. The |
744 | alpha value is a linear measure of the contribution of the | 744 | alpha value is a linear measure of the contribution of the |
745 | pixel to the corresponding final output pixel. | 745 | pixel to the corresponding final output pixel. |
746 | 746 | ||
747 | You should normally use this format if you intend to perform | 747 | You should normally use this format if you intend to perform |
748 | color correction on the color values; most, maybe all, color | 748 | color correction on the color values; most, maybe all, color |
749 | correction software has no handling for the alpha channel and, | 749 | correction software has no handling for the alpha channel and, |
750 | anyway, the math to handle pre-multiplied component values is | 750 | anyway, the math to handle pre-multiplied component values is |
751 | unnecessarily complex. | 751 | unnecessarily complex. |
752 | 752 | ||
753 | Before you do any arithmetic on the component values you need | 753 | Before you do any arithmetic on the component values you need |
754 | to remove the gamma encoding and multiply out the alpha | 754 | to remove the gamma encoding and multiply out the alpha |
755 | channel. See the PNG specification for more detail. It is | 755 | channel. See the PNG specification for more detail. It is |
756 | important to note that when an image with an alpha channel is | 756 | important to note that when an image with an alpha channel is |
757 | scaled, linear encoded, pre-multiplied component values must | 757 | scaled, linear encoded, pre-multiplied component values must |
758 | be used! | 758 | be used! |
759 | 759 | ||
760 | The remaining modes assume you don't need to do any further color correction or | 760 | The remaining modes assume you don't need to do any further color correction or |
761 | that if you do, your color correction software knows all about alpha (it | 761 | that if you do, your color correction software knows all about alpha (it |
762 | probably doesn't!) | 762 | probably doesn't!) |
763 | 763 | ||
764 | PNG_ALPHA_STANDARD: The data libpng produces | 764 | PNG_ALPHA_STANDARD: The data libpng produces |
765 | is encoded in the standard way | 765 | is encoded in the standard way |
766 | assumed by most correctly written graphics software. | 766 | assumed by most correctly written graphics software. |
767 | The gamma encoding will be removed by libpng and the | 767 | The gamma encoding will be removed by libpng and the |
768 | linear component values will be pre-multiplied by the | 768 | linear component values will be pre-multiplied by the |
769 | alpha channel. | 769 | alpha channel. |
770 | 770 | ||
771 | With this format the final image must be re-encoded to | 771 | With this format the final image must be re-encoded to |
772 | match the display gamma before the image is displayed. | 772 | match the display gamma before the image is displayed. |
773 | If your system doesn't do that, yet still seems to | 773 | If your system doesn't do that, yet still seems to |
774 | perform arithmetic on the pixels without decoding them, | 774 | perform arithmetic on the pixels without decoding them, |
775 | it is broken - check out the modes below. | 775 | it is broken - check out the modes below. |
776 | 776 | ||
777 | With PNG_ALPHA_STANDARD libpng always produces linear | 777 | With PNG_ALPHA_STANDARD libpng always produces linear |
778 | component values, whatever screen_gamma you supply. The | 778 | component values, whatever screen_gamma you supply. The |
779 | screen_gamma value is, however, used as a default for | 779 | screen_gamma value is, however, used as a default for |
780 | the file gamma if the PNG file has no gamma information. | 780 | the file gamma if the PNG file has no gamma information. |
781 | 781 | ||
782 | If you call png_set_gamma() after png_set_alpha_mode() you | 782 | If you call png_set_gamma() after png_set_alpha_mode() you |
783 | will override the linear encoding. Instead the | 783 | will override the linear encoding. Instead the |
784 | pre-multiplied pixel values will be gamma encoded but | 784 | pre-multiplied pixel values will be gamma encoded but |
785 | the alpha channel will still be linear. This may | 785 | the alpha channel will still be linear. This may |
786 | actually match the requirements of some broken software, | 786 | actually match the requirements of some broken software, |
787 | but it is unlikely. | 787 | but it is unlikely. |
788 | 788 | ||
789 | While linear 8-bit data is often used it has | 789 | While linear 8-bit data is often used it has |
790 | insufficient precision for any image with a reasonable | 790 | insufficient precision for any image with a reasonable |
791 | dynamic range. To avoid problems, and if your software | 791 | dynamic range. To avoid problems, and if your software |
792 | supports it, use png_set_expand_16() to force all | 792 | supports it, use png_set_expand_16() to force all |
793 | components to 16 bits. | 793 | components to 16 bits. |
794 | 794 | ||
795 | PNG_ALPHA_OPTIMIZED: This mode is the same | 795 | PNG_ALPHA_OPTIMIZED: This mode is the same |
796 | as PNG_ALPHA_STANDARD except that | 796 | as PNG_ALPHA_STANDARD except that |
797 | completely opaque pixels are gamma encoded according to | 797 | completely opaque pixels are gamma encoded according to |
798 | the screen_gamma value. Pixels with alpha less than 1.0 | 798 | the screen_gamma value. Pixels with alpha less than 1.0 |
799 | will still have linear components. | 799 | will still have linear components. |
800 | 800 | ||
801 | Use this format if you have control over your | 801 | Use this format if you have control over your |
802 | compositing software and do don't do other arithmetic | 802 | compositing software and do don't do other arithmetic |
803 | (such as scaling) on the data you get from libpng. Your | 803 | (such as scaling) on the data you get from libpng. Your |
804 | compositing software can simply copy opaque pixels to | 804 | compositing software can simply copy opaque pixels to |
805 | the output but still has linear values for the | 805 | the output but still has linear values for the |
806 | non-opaque pixels. | 806 | non-opaque pixels. |
807 | 807 | ||
808 | In normal compositing, where the alpha channel encodes | 808 | In normal compositing, where the alpha channel encodes |
809 | partial pixel coverage (as opposed to broad area | 809 | partial pixel coverage (as opposed to broad area |
810 | translucency), the inaccuracies of the 8-bit | 810 | translucency), the inaccuracies of the 8-bit |
811 | representation of non-opaque pixels are irrelevant. | 811 | representation of non-opaque pixels are irrelevant. |
812 | 812 | ||
813 | You can also try this format if your software is broken; | 813 | You can also try this format if your software is broken; |
814 | it might look better. | 814 | it might look better. |
815 | 815 | ||
816 | PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; | 816 | PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; |
817 | however, all component values, | 817 | however, all component values, |
818 | including the alpha channel are gamma encoded. This is | 818 | including the alpha channel are gamma encoded. This is |
819 | an appropriate format to try if your software, or more | 819 | an appropriate format to try if your software, or more |
820 | likely hardware, is totally broken, i.e., if it performs | 820 | likely hardware, is totally broken, i.e., if it performs |
821 | linear arithmetic directly on gamma encoded values. | 821 | linear arithmetic directly on gamma encoded values. |
822 | 822 | ||
823 | In most cases of broken software or hardware the bug in the final display | 823 | In most cases of broken software or hardware the bug in the final display |
824 | manifests as a subtle halo around composited parts of the image. You may not | 824 | manifests as a subtle halo around composited parts of the image. You may not |
825 | even perceive this as a halo; the composited part of the image may simply appear | 825 | even perceive this as a halo; the composited part of the image may simply appear |
826 | separate from the background, as though it had been cut out of paper and pasted | 826 | separate from the background, as though it had been cut out of paper and pasted |
827 | on afterward. | 827 | on afterward. |
828 | 828 | ||
829 | If you don't have to deal with bugs in software or hardware, or if you can fix | 829 | If you don't have to deal with bugs in software or hardware, or if you can fix |
830 | them, there are three recommended ways of using png_set_alpha_mode(): | 830 | them, there are three recommended ways of using png_set_alpha_mode(): |
831 | 831 | ||
832 | png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG, | 832 | png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG, |
833 | screen_gamma); | 833 | screen_gamma); |
834 | 834 | ||
835 | You can do color correction on the result (libpng does not currently | 835 | You can do color correction on the result (libpng does not currently |
836 | support color correction internally). When you handle the alpha channel | 836 | support color correction internally). When you handle the alpha channel |
837 | you need to undo the gamma encoding and multiply out the alpha. | 837 | you need to undo the gamma encoding and multiply out the alpha. |
838 | 838 | ||
839 | png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD, | 839 | png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD, |
840 | screen_gamma); | 840 | screen_gamma); |
841 | png_set_expand_16(png_ptr); | 841 | png_set_expand_16(png_ptr); |
842 | 842 | ||
843 | If you are using the high level interface, don't call png_set_expand_16(); | 843 | If you are using the high level interface, don't call png_set_expand_16(); |
844 | instead pass PNG_TRANSFORM_EXPAND_16 to the interface. | 844 | instead pass PNG_TRANSFORM_EXPAND_16 to the interface. |
845 | 845 | ||
846 | With this mode you can't do color correction, but you can do arithmetic, | 846 | With this mode you can't do color correction, but you can do arithmetic, |
847 | including composition and scaling, on the data without further processing. | 847 | including composition and scaling, on the data without further processing. |
848 | 848 | ||
849 | png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED, | 849 | png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED, |
850 | screen_gamma); | 850 | screen_gamma); |
851 | 851 | ||
852 | You can avoid the expansion to 16-bit components with this mode, but you | 852 | You can avoid the expansion to 16-bit components with this mode, but you |
853 | lose the ability to scale the image or perform other linear arithmetic. | 853 | lose the ability to scale the image or perform other linear arithmetic. |
854 | All you can do is compose the result onto a matching output. Since this | 854 | All you can do is compose the result onto a matching output. Since this |
855 | mode is libpng-specific you also need to write your own composition | 855 | mode is libpng-specific you also need to write your own composition |
856 | software. | 856 | software. |
857 | 857 | ||
858 | If you don't need, or can't handle, the alpha channel you can call | 858 | If you don't need, or can't handle, the alpha channel you can call |
859 | png_set_background() to remove it by compositing against a fixed color. Don't | 859 | png_set_background() to remove it by compositing against a fixed color. Don't |
860 | call png_set_strip_alpha() to do this - it will leave spurious pixel values in | 860 | call png_set_strip_alpha() to do this - it will leave spurious pixel values in |
861 | transparent parts of this image. | 861 | transparent parts of this image. |
862 | 862 | ||
863 | png_set_background(png_ptr, &background_color, | 863 | png_set_background(png_ptr, &background_color, |
864 | PNG_BACKGROUND_GAMMA_SCREEN, 0, 1); | 864 | PNG_BACKGROUND_GAMMA_SCREEN, 0, 1); |
865 | 865 | ||
866 | The background_color is an RGB or grayscale value according to the data format | 866 | The background_color is an RGB or grayscale value according to the data format |
867 | libpng will produce for you. Because you don't yet know the format of the PNG | 867 | libpng will produce for you. Because you don't yet know the format of the PNG |
868 | file, if you call png_set_background at this point you must arrange for the | 868 | file, if you call png_set_background at this point you must arrange for the |
869 | format produced by libpng to always have 8-bit or 16-bit components and then | 869 | format produced by libpng to always have 8-bit or 16-bit components and then |
870 | store the color as an 8-bit or 16-bit color as appropriate. The color contains | 870 | store the color as an 8-bit or 16-bit color as appropriate. The color contains |
871 | separate gray and RGB component values, so you can let libpng produce gray or | 871 | separate gray and RGB component values, so you can let libpng produce gray or |
872 | RGB output according to the input format, but low bit depth grayscale images | 872 | RGB output according to the input format, but low bit depth grayscale images |
873 | must always be converted to at least 8-bit format. (Even though low bit depth | 873 | must always be converted to at least 8-bit format. (Even though low bit depth |
874 | grayscale images can't have an alpha channel they can have a transparent | 874 | grayscale images can't have an alpha channel they can have a transparent |
875 | color!) | 875 | color!) |
876 | 876 | ||
877 | You set the transforms you need later, either as flags to the high level | 877 | You set the transforms you need later, either as flags to the high level |
878 | interface or libpng API calls for the low level interface. For reference the | 878 | interface or libpng API calls for the low level interface. For reference the |
879 | settings and API calls required are: | 879 | settings and API calls required are: |
880 | 880 | ||
881 | 8-bit values: | 881 | 8-bit values: |
882 | PNG_TRANSFORM_SCALE_16 | PNG_EXPAND | 882 | PNG_TRANSFORM_SCALE_16 | PNG_EXPAND |
883 | png_set_expand(png_ptr); png_set_scale_16(png_ptr); | 883 | png_set_expand(png_ptr); png_set_scale_16(png_ptr); |
884 | 884 | ||
885 | If you must get exactly the same inaccurate results | 885 | If you must get exactly the same inaccurate results |
886 | produced by default in versions prior to libpng-1.5.4, | 886 | produced by default in versions prior to libpng-1.5.4, |
887 | use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr) | 887 | use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr) |
888 | instead. | 888 | instead. |
889 | 889 | ||
890 | 16-bit values: | 890 | 16-bit values: |
891 | PNG_TRANSFORM_EXPAND_16 | 891 | PNG_TRANSFORM_EXPAND_16 |
892 | png_set_expand_16(png_ptr); | 892 | png_set_expand_16(png_ptr); |
893 | 893 | ||
894 | In either case palette image data will be expanded to RGB. If you just want | 894 | In either case palette image data will be expanded to RGB. If you just want |
895 | color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr) | 895 | color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr) |
896 | to the list. | 896 | to the list. |
897 | 897 | ||
898 | Calling png_set_background before the PNG file header is read will not work | 898 | Calling png_set_background before the PNG file header is read will not work |
899 | prior to libpng-1.5.4. Because the failure may result in unexpected warnings or | 899 | prior to libpng-1.5.4. Because the failure may result in unexpected warnings or |
900 | errors it is therefore much safer to call png_set_background after the head has | 900 | errors it is therefore much safer to call png_set_background after the head has |
901 | been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be | 901 | been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be |
902 | used with the high level interface. | 902 | used with the high level interface. |
903 | 903 | ||
904 | The high-level read interface | 904 | The high-level read interface |
905 | 905 | ||
906 | At this point there are two ways to proceed; through the high-level | 906 | At this point there are two ways to proceed; through the high-level |
907 | read interface, or through a sequence of low-level read operations. | 907 | read interface, or through a sequence of low-level read operations. |
908 | You can use the high-level interface if (a) you are willing to read | 908 | You can use the high-level interface if (a) you are willing to read |
909 | the entire image into memory, and (b) the input transformations | 909 | the entire image into memory, and (b) the input transformations |
910 | you want to do are limited to the following set: | 910 | you want to do are limited to the following set: |
911 | 911 | ||
912 | PNG_TRANSFORM_IDENTITY No transformation | 912 | PNG_TRANSFORM_IDENTITY No transformation |
913 | PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to | 913 | PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to |
914 | 8-bit accurately | 914 | 8-bit accurately |
915 | PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to | 915 | PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to |
916 | 8-bit less accurately | 916 | 8-bit less accurately |
917 | PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel | 917 | PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel |
918 | PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit | 918 | PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit |
919 | samples to bytes | 919 | samples to bytes |
920 | PNG_TRANSFORM_PACKSWAP Change order of packed | 920 | PNG_TRANSFORM_PACKSWAP Change order of packed |
921 | pixels to LSB first | 921 | pixels to LSB first |
922 | PNG_TRANSFORM_EXPAND Perform set_expand() | 922 | PNG_TRANSFORM_EXPAND Perform set_expand() |
923 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images | 923 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images |
924 | PNG_TRANSFORM_SHIFT Normalize pixels to the | 924 | PNG_TRANSFORM_SHIFT Normalize pixels to the |
925 | sBIT depth | 925 | sBIT depth |
926 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA | 926 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA |
927 | to BGRA | 927 | to BGRA |
928 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA | 928 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA |
929 | to AG | 929 | to AG |
930 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity | 930 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity |
931 | to transparency | 931 | to transparency |
932 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples | 932 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples |
933 | PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples | 933 | PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples |
934 | to RGB (or GA to RGBA) | 934 | to RGB (or GA to RGBA) |
935 | PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits | 935 | PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits |
936 | 936 | ||
937 | (This excludes setting a background color, doing gamma transformation, | 937 | (This excludes setting a background color, doing gamma transformation, |
938 | quantizing, and setting filler.) If this is the case, simply do this: | 938 | quantizing, and setting filler.) If this is the case, simply do this: |
939 | 939 | ||
940 | png_read_png(png_ptr, info_ptr, png_transforms, NULL) | 940 | png_read_png(png_ptr, info_ptr, png_transforms, NULL) |
941 | 941 | ||
942 | where png_transforms is an integer containing the bitwise OR of some | 942 | where png_transforms is an integer containing the bitwise OR of some |
943 | set of transformation flags. This call is equivalent to png_read_info(), | 943 | set of transformation flags. This call is equivalent to png_read_info(), |
944 | followed the set of transformations indicated by the transform mask, | 944 | followed the set of transformations indicated by the transform mask, |
945 | then png_read_image(), and finally png_read_end(). | 945 | then png_read_image(), and finally png_read_end(). |
946 | 946 | ||
947 | (The final parameter of this call is not yet used. Someday it might point | 947 | (The final parameter of this call is not yet used. Someday it might point |
948 | to transformation parameters required by some future input transform.) | 948 | to transformation parameters required by some future input transform.) |
949 | 949 | ||
950 | You must use png_transforms and not call any png_set_transform() functions | 950 | You must use png_transforms and not call any png_set_transform() functions |
951 | when you use png_read_png(). | 951 | when you use png_read_png(). |
952 | 952 | ||
953 | After you have called png_read_png(), you can retrieve the image data | 953 | After you have called png_read_png(), you can retrieve the image data |
954 | with | 954 | with |
955 | 955 | ||
956 | row_pointers = png_get_rows(png_ptr, info_ptr); | 956 | row_pointers = png_get_rows(png_ptr, info_ptr); |
957 | 957 | ||
958 | where row_pointers is an array of pointers to the pixel data for each row: | 958 | where row_pointers is an array of pointers to the pixel data for each row: |
959 | 959 | ||
960 | png_bytep row_pointers[height]; | 960 | png_bytep row_pointers[height]; |
961 | 961 | ||
962 | If you know your image size and pixel size ahead of time, you can allocate | 962 | If you know your image size and pixel size ahead of time, you can allocate |
963 | row_pointers prior to calling png_read_png() with | 963 | row_pointers prior to calling png_read_png() with |
964 | 964 | ||
965 | if (height > PNG_UINT_32_MAX/png_sizeof(png_byte)) | 965 | if (height > PNG_UINT_32_MAX/png_sizeof(png_byte)) |
966 | png_error (png_ptr, | 966 | png_error (png_ptr, |
967 | "Image is too tall to process in memory"); | 967 | "Image is too tall to process in memory"); |
968 | 968 | ||
969 | if (width > PNG_UINT_32_MAX/pixel_size) | 969 | if (width > PNG_UINT_32_MAX/pixel_size) |
970 | png_error (png_ptr, | 970 | png_error (png_ptr, |
971 | "Image is too wide to process in memory"); | 971 | "Image is too wide to process in memory"); |
972 | 972 | ||
973 | row_pointers = png_malloc(png_ptr, | 973 | row_pointers = png_malloc(png_ptr, |
974 | height*png_sizeof(png_bytep)); | 974 | height*png_sizeof(png_bytep)); |
975 | 975 | ||
976 | for (int i=0; i<height, i++) | 976 | for (int i=0; i<height, i++) |
977 | row_pointers[i]=NULL; /* security precaution */ | 977 | row_pointers[i]=NULL; /* security precaution */ |
978 | 978 | ||
979 | for (int i=0; i<height, i++) | 979 | for (int i=0; i<height, i++) |
980 | row_pointers[i]=png_malloc(png_ptr, | 980 | row_pointers[i]=png_malloc(png_ptr, |
981 | width*pixel_size); | 981 | width*pixel_size); |
982 | 982 | ||
983 | png_set_rows(png_ptr, info_ptr, &row_pointers); | 983 | png_set_rows(png_ptr, info_ptr, &row_pointers); |
984 | 984 | ||
985 | Alternatively you could allocate your image in one big block and define | 985 | Alternatively you could allocate your image in one big block and define |
986 | row_pointers[i] to point into the proper places in your block. | 986 | row_pointers[i] to point into the proper places in your block. |
987 | 987 | ||
988 | If you use png_set_rows(), the application is responsible for freeing | 988 | If you use png_set_rows(), the application is responsible for freeing |
989 | row_pointers (and row_pointers[i], if they were separately allocated). | 989 | row_pointers (and row_pointers[i], if they were separately allocated). |
990 | 990 | ||
991 | If you don't allocate row_pointers ahead of time, png_read_png() will | 991 | If you don't allocate row_pointers ahead of time, png_read_png() will |
992 | do it, and it'll be free'ed by libpng when you call png_destroy_*(). | 992 | do it, and it'll be free'ed by libpng when you call png_destroy_*(). |
993 | 993 | ||
994 | The low-level read interface | 994 | The low-level read interface |
995 | 995 | ||
996 | If you are going the low-level route, you are now ready to read all | 996 | If you are going the low-level route, you are now ready to read all |
997 | the file information up to the actual image data. You do this with a | 997 | the file information up to the actual image data. You do this with a |
998 | call to png_read_info(). | 998 | call to png_read_info(). |
999 | 999 | ||
1000 | png_read_info(png_ptr, info_ptr); | 1000 | png_read_info(png_ptr, info_ptr); |
1001 | 1001 | ||
1002 | This will process all chunks up to but not including the image data. | 1002 | This will process all chunks up to but not including the image data. |
1003 | 1003 | ||
1004 | This also copies some of the data from the PNG file into the decode structure | 1004 | This also copies some of the data from the PNG file into the decode structure |
1005 | for use in later transformations. Important information copied in is: | 1005 | for use in later transformations. Important information copied in is: |
1006 | 1006 | ||
1007 | 1) The PNG file gamma from the gAMA chunk. This overwrites the default value | 1007 | 1) The PNG file gamma from the gAMA chunk. This overwrites the default value |
1008 | provided by an earlier call to png_set_gamma or png_set_alpha_mode. | 1008 | provided by an earlier call to png_set_gamma or png_set_alpha_mode. |
1009 | 1009 | ||
1010 | 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This | 1010 | 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This |
1011 | damages the information provided by an earlier call to png_set_background | 1011 | damages the information provided by an earlier call to png_set_background |
1012 | resulting in unexpected behavior. Libpng-1.5.4 no longer does this. | 1012 | resulting in unexpected behavior. Libpng-1.5.4 no longer does this. |
1013 | 1013 | ||
1014 | 3) The number of significant bits in each component value. Libpng uses this to | 1014 | 3) The number of significant bits in each component value. Libpng uses this to |
1015 | optimize gamma handling by reducing the internal lookup table sizes. | 1015 | optimize gamma handling by reducing the internal lookup table sizes. |
1016 | 1016 | ||
1017 | 4) The transparent color information from a tRNS chunk. This can be modified by | 1017 | 4) The transparent color information from a tRNS chunk. This can be modified by |
1018 | a later call to png_set_tRNS. | 1018 | a later call to png_set_tRNS. |
1019 | 1019 | ||
1020 | Querying the info structure | 1020 | Querying the info structure |
1021 | 1021 | ||
1022 | Functions are used to get the information from the info_ptr once it | 1022 | Functions are used to get the information from the info_ptr once it |
1023 | has been read. Note that these fields may not be completely filled | 1023 | has been read. Note that these fields may not be completely filled |
1024 | in until png_read_end() has read the chunk data following the image. | 1024 | in until png_read_end() has read the chunk data following the image. |
1025 | 1025 | ||
1026 | png_get_IHDR(png_ptr, info_ptr, &width, &height, | 1026 | png_get_IHDR(png_ptr, info_ptr, &width, &height, |
1027 | &bit_depth, &color_type, &interlace_type, | 1027 | &bit_depth, &color_type, &interlace_type, |
1028 | &compression_type, &filter_method); | 1028 | &compression_type, &filter_method); |
1029 | 1029 | ||
1030 | width - holds the width of the image | 1030 | width - holds the width of the image |
1031 | in pixels (up to 2^31). | 1031 | in pixels (up to 2^31). |
1032 | 1032 | ||
1033 | height - holds the height of the image | 1033 | height - holds the height of the image |
1034 | in pixels (up to 2^31). | 1034 | in pixels (up to 2^31). |
1035 | 1035 | ||
1036 | bit_depth - holds the bit depth of one of the | 1036 | bit_depth - holds the bit depth of one of the |
1037 | image channels. (valid values are | 1037 | image channels. (valid values are |
1038 | 1, 2, 4, 8, 16 and depend also on | 1038 | 1, 2, 4, 8, 16 and depend also on |
1039 | the color_type. See also | 1039 | the color_type. See also |
1040 | significant bits (sBIT) below). | 1040 | significant bits (sBIT) below). |
1041 | 1041 | ||
1042 | color_type - describes which color/alpha channels | 1042 | color_type - describes which color/alpha channels |
1043 | are present. | 1043 | are present. |
1044 | PNG_COLOR_TYPE_GRAY | 1044 | PNG_COLOR_TYPE_GRAY |
1045 | (bit depths 1, 2, 4, 8, 16) | 1045 | (bit depths 1, 2, 4, 8, 16) |
1046 | PNG_COLOR_TYPE_GRAY_ALPHA | 1046 | PNG_COLOR_TYPE_GRAY_ALPHA |
1047 | (bit depths 8, 16) | 1047 | (bit depths 8, 16) |
1048 | PNG_COLOR_TYPE_PALETTE | 1048 | PNG_COLOR_TYPE_PALETTE |
1049 | (bit depths 1, 2, 4, 8) | 1049 | (bit depths 1, 2, 4, 8) |
1050 | PNG_COLOR_TYPE_RGB | 1050 | PNG_COLOR_TYPE_RGB |
1051 | (bit_depths 8, 16) | 1051 | (bit_depths 8, 16) |
1052 | PNG_COLOR_TYPE_RGB_ALPHA | 1052 | PNG_COLOR_TYPE_RGB_ALPHA |
1053 | (bit_depths 8, 16) | 1053 | (bit_depths 8, 16) |
1054 | 1054 | ||
1055 | PNG_COLOR_MASK_PALETTE | 1055 | PNG_COLOR_MASK_PALETTE |
1056 | PNG_COLOR_MASK_COLOR | 1056 | PNG_COLOR_MASK_COLOR |
1057 | PNG_COLOR_MASK_ALPHA | 1057 | PNG_COLOR_MASK_ALPHA |
1058 | 1058 | ||
1059 | interlace_type - (PNG_INTERLACE_NONE or | 1059 | interlace_type - (PNG_INTERLACE_NONE or |
1060 | PNG_INTERLACE_ADAM7) | 1060 | PNG_INTERLACE_ADAM7) |
1061 | 1061 | ||
1062 | compression_type - (must be PNG_COMPRESSION_TYPE_BASE | 1062 | compression_type - (must be PNG_COMPRESSION_TYPE_BASE |
1063 | for PNG 1.0) | 1063 | for PNG 1.0) |
1064 | 1064 | ||
1065 | filter_method - (must be PNG_FILTER_TYPE_BASE | 1065 | filter_method - (must be PNG_FILTER_TYPE_BASE |
1066 | for PNG 1.0, and can also be | 1066 | for PNG 1.0, and can also be |
1067 | PNG_INTRAPIXEL_DIFFERENCING if | 1067 | PNG_INTRAPIXEL_DIFFERENCING if |
1068 | the PNG datastream is embedded in | 1068 | the PNG datastream is embedded in |
1069 | a MNG-1.0 datastream) | 1069 | a MNG-1.0 datastream) |
1070 | 1070 | ||
1071 | Any or all of interlace_type, compression_type, or | 1071 | Any or all of interlace_type, compression_type, or |
1072 | filter_method can be NULL if you are | 1072 | filter_method can be NULL if you are |
1073 | not interested in their values. | 1073 | not interested in their values. |
1074 | 1074 | ||
1075 | Note that png_get_IHDR() returns 32-bit data into | 1075 | Note that png_get_IHDR() returns 32-bit data into |
1076 | the application's width and height variables. | 1076 | the application's width and height variables. |
1077 | This is an unsafe situation if these are 16-bit | 1077 | This is an unsafe situation if these are 16-bit |
1078 | variables. In such situations, the | 1078 | variables. In such situations, the |
1079 | png_get_image_width() and png_get_image_height() | 1079 | png_get_image_width() and png_get_image_height() |
1080 | functions described below are safer. | 1080 | functions described below are safer. |
1081 | 1081 | ||
1082 | width = png_get_image_width(png_ptr, | 1082 | width = png_get_image_width(png_ptr, |
1083 | info_ptr); | 1083 | info_ptr); |
1084 | 1084 | ||
1085 | height = png_get_image_height(png_ptr, | 1085 | height = png_get_image_height(png_ptr, |
1086 | info_ptr); | 1086 | info_ptr); |
1087 | 1087 | ||
1088 | bit_depth = png_get_bit_depth(png_ptr, | 1088 | bit_depth = png_get_bit_depth(png_ptr, |
1089 | info_ptr); | 1089 | info_ptr); |
1090 | 1090 | ||
1091 | color_type = png_get_color_type(png_ptr, | 1091 | color_type = png_get_color_type(png_ptr, |
1092 | info_ptr); | 1092 | info_ptr); |
1093 | 1093 | ||
1094 | interlace_type = png_get_interlace_type(png_ptr, | 1094 | interlace_type = png_get_interlace_type(png_ptr, |
1095 | info_ptr); | 1095 | info_ptr); |
1096 | 1096 | ||
1097 | compression_type = png_get_compression_type(png_ptr, | 1097 | compression_type = png_get_compression_type(png_ptr, |
1098 | info_ptr); | 1098 | info_ptr); |
1099 | 1099 | ||
1100 | filter_method = png_get_filter_type(png_ptr, | 1100 | filter_method = png_get_filter_type(png_ptr, |
1101 | info_ptr); | 1101 | info_ptr); |
1102 | 1102 | ||
1103 | channels = png_get_channels(png_ptr, info_ptr); | 1103 | channels = png_get_channels(png_ptr, info_ptr); |
1104 | 1104 | ||
1105 | channels - number of channels of info for the | 1105 | channels - number of channels of info for the |
1106 | color type (valid values are 1 (GRAY, | 1106 | color type (valid values are 1 (GRAY, |
1107 | PALETTE), 2 (GRAY_ALPHA), 3 (RGB), | 1107 | PALETTE), 2 (GRAY_ALPHA), 3 (RGB), |
1108 | 4 (RGB_ALPHA or RGB + filler byte)) | 1108 | 4 (RGB_ALPHA or RGB + filler byte)) |
1109 | 1109 | ||
1110 | rowbytes = png_get_rowbytes(png_ptr, info_ptr); | 1110 | rowbytes = png_get_rowbytes(png_ptr, info_ptr); |
1111 | 1111 | ||
1112 | rowbytes - number of bytes needed to hold a row | 1112 | rowbytes - number of bytes needed to hold a row |
1113 | 1113 | ||
1114 | signature = png_get_signature(png_ptr, info_ptr); | 1114 | signature = png_get_signature(png_ptr, info_ptr); |
1115 | 1115 | ||
1116 | signature - holds the signature read from the | 1116 | signature - holds the signature read from the |
1117 | file (if any). The data is kept in | 1117 | file (if any). The data is kept in |
1118 | the same offset it would be if the | 1118 | the same offset it would be if the |
1119 | whole signature were read (i.e. if an | 1119 | whole signature were read (i.e. if an |
1120 | application had already read in 4 | 1120 | application had already read in 4 |
1121 | bytes of signature before starting | 1121 | bytes of signature before starting |
1122 | libpng, the remaining 4 bytes would | 1122 | libpng, the remaining 4 bytes would |
1123 | be in signature[4] through signature[7] | 1123 | be in signature[4] through signature[7] |
1124 | (see png_set_sig_bytes())). | 1124 | (see png_set_sig_bytes())). |
1125 | 1125 | ||
1126 | These are also important, but their validity depends on whether the chunk | 1126 | These are also important, but their validity depends on whether the chunk |
1127 | has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and | 1127 | has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and |
1128 | png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the | 1128 | png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the |
1129 | data has been read, or zero if it is missing. The parameters to the | 1129 | data has been read, or zero if it is missing. The parameters to the |
1130 | png_get_<chunk> are set directly if they are simple data types, or a | 1130 | png_get_<chunk> are set directly if they are simple data types, or a |
1131 | pointer into the info_ptr is returned for any complex types. | 1131 | pointer into the info_ptr is returned for any complex types. |
1132 | 1132 | ||
1133 | png_get_PLTE(png_ptr, info_ptr, &palette, | 1133 | png_get_PLTE(png_ptr, info_ptr, &palette, |
1134 | &num_palette); | 1134 | &num_palette); |
1135 | 1135 | ||
1136 | palette - the palette for the file | 1136 | palette - the palette for the file |
1137 | (array of png_color) | 1137 | (array of png_color) |
1138 | 1138 | ||
1139 | num_palette - number of entries in the palette | 1139 | num_palette - number of entries in the palette |
1140 | 1140 | ||
1141 | png_get_gAMA(png_ptr, info_ptr, &file_gamma); | 1141 | png_get_gAMA(png_ptr, info_ptr, &file_gamma); |
1142 | png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma); | 1142 | png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma); |
1143 | 1143 | ||
1144 | file_gamma - the gamma at which the file is | 1144 | file_gamma - the gamma at which the file is |
1145 | written (PNG_INFO_gAMA) | 1145 | written (PNG_INFO_gAMA) |
1146 | 1146 | ||
1147 | int_file_gamma - 100,000 times the gamma at which the | 1147 | int_file_gamma - 100,000 times the gamma at which the |
1148 | file is written | 1148 | file is written |
1149 | 1149 | ||
1150 | png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y, | 1150 | png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x, &red_y, |
1151 | &green_x, &green_y, &blue_x, &blue_y) | 1151 | &green_x, &green_y, &blue_x, &blue_y) |
1152 | png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X, | 1152 | png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z, &green_X, |
1153 | &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z) | 1153 | &green_Y, &green_Z, &blue_X, &blue_Y, &blue_Z) |
1154 | png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y, | 1154 | png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x, &int_white_y, |
1155 | &int_red_x, &int_red_y, &int_green_x, &int_green_y, | 1155 | &int_red_x, &int_red_y, &int_green_x, &int_green_y, |
1156 | &int_blue_x, &int_blue_y) | 1156 | &int_blue_x, &int_blue_y) |
1157 | png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y, | 1157 | png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y, |
1158 | &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z, | 1158 | &int_red_Z, &int_green_X, &int_green_Y, &int_green_Z, |
1159 | &int_blue_X, &int_blue_Y, &int_blue_Z) | 1159 | &int_blue_X, &int_blue_Y, &int_blue_Z) |
1160 | 1160 | ||
1161 | {white,red,green,blue}_{x,y} | 1161 | {white,red,green,blue}_{x,y} |
1162 | A color space encoding specified using the chromaticities | 1162 | A color space encoding specified using the chromaticities |
1163 | of the end points and the white point. (PNG_INFO_cHRM) | 1163 | of the end points and the white point. (PNG_INFO_cHRM) |
1164 | 1164 | ||
1165 | {red,green,blue}_{X,Y,Z} | 1165 | {red,green,blue}_{X,Y,Z} |
1166 | A color space encoding specified using the encoding end | 1166 | A color space encoding specified using the encoding end |
1167 | points - the CIE tristimulus specification of the intended | 1167 | points - the CIE tristimulus specification of the intended |
1168 | color of the red, green and blue channels in the PNG RGB | 1168 | color of the red, green and blue channels in the PNG RGB |
1169 | data. The white point is simply the sum of the three end | 1169 | data. The white point is simply the sum of the three end |
1170 | points. (PNG_INFO_cHRM) | 1170 | points. (PNG_INFO_cHRM) |
1171 | 1171 | ||
1172 | png_get_sRGB(png_ptr, info_ptr, &srgb_intent); | 1172 | png_get_sRGB(png_ptr, info_ptr, &srgb_intent); |
1173 | 1173 | ||
1174 | file_srgb_intent - the rendering intent (PNG_INFO_sRGB) | 1174 | file_srgb_intent - the rendering intent (PNG_INFO_sRGB) |
1175 | The presence of the sRGB chunk | 1175 | The presence of the sRGB chunk |
1176 | means that the pixel data is in the | 1176 | means that the pixel data is in the |
1177 | sRGB color space. This chunk also | 1177 | sRGB color space. This chunk also |
1178 | implies specific values of gAMA and | 1178 | implies specific values of gAMA and |
1179 | cHRM. | 1179 | cHRM. |
1180 | 1180 | ||
1181 | png_get_iCCP(png_ptr, info_ptr, &name, | 1181 | png_get_iCCP(png_ptr, info_ptr, &name, |
1182 | &compression_type, &profile, &proflen); | 1182 | &compression_type, &profile, &proflen); |
1183 | 1183 | ||
1184 | name - The profile name. | 1184 | name - The profile name. |
1185 | 1185 | ||
1186 | compression_type - The compression type; always | 1186 | compression_type - The compression type; always |
1187 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. | 1187 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. |
1188 | You may give NULL to this argument to | 1188 | You may give NULL to this argument to |
1189 | ignore it. | 1189 | ignore it. |
1190 | 1190 | ||
1191 | profile - International Color Consortium color | 1191 | profile - International Color Consortium color |
1192 | profile data. May contain NULs. | 1192 | profile data. May contain NULs. |
1193 | 1193 | ||
1194 | proflen - length of profile data in bytes. | 1194 | proflen - length of profile data in bytes. |
1195 | 1195 | ||
1196 | png_get_sBIT(png_ptr, info_ptr, &sig_bit); | 1196 | png_get_sBIT(png_ptr, info_ptr, &sig_bit); |
1197 | 1197 | ||
1198 | sig_bit - the number of significant bits for | 1198 | sig_bit - the number of significant bits for |
1199 | (PNG_INFO_sBIT) each of the gray, | 1199 | (PNG_INFO_sBIT) each of the gray, |
1200 | red, green, and blue channels, | 1200 | red, green, and blue channels, |
1201 | whichever are appropriate for the | 1201 | whichever are appropriate for the |
1202 | given color type (png_color_16) | 1202 | given color type (png_color_16) |
1203 | 1203 | ||
1204 | png_get_tRNS(png_ptr, info_ptr, &trans_alpha, | 1204 | png_get_tRNS(png_ptr, info_ptr, &trans_alpha, |
1205 | &num_trans, &trans_color); | 1205 | &num_trans, &trans_color); |
1206 | 1206 | ||
1207 | trans_alpha - array of alpha (transparency) | 1207 | trans_alpha - array of alpha (transparency) |
1208 | entries for palette (PNG_INFO_tRNS) | 1208 | entries for palette (PNG_INFO_tRNS) |
1209 | 1209 | ||
1210 | num_trans - number of transparent entries | 1210 | num_trans - number of transparent entries |
1211 | (PNG_INFO_tRNS) | 1211 | (PNG_INFO_tRNS) |
1212 | 1212 | ||
1213 | trans_color - graylevel or color sample values of | 1213 | trans_color - graylevel or color sample values of |
1214 | the single transparent color for | 1214 | the single transparent color for |
1215 | non-paletted images (PNG_INFO_tRNS) | 1215 | non-paletted images (PNG_INFO_tRNS) |
1216 | 1216 | ||
1217 | png_get_hIST(png_ptr, info_ptr, &hist); | 1217 | png_get_hIST(png_ptr, info_ptr, &hist); |
1218 | (PNG_INFO_hIST) | 1218 | (PNG_INFO_hIST) |
1219 | 1219 | ||
1220 | hist - histogram of palette (array of | 1220 | hist - histogram of palette (array of |
1221 | png_uint_16) | 1221 | png_uint_16) |
1222 | 1222 | ||
1223 | png_get_tIME(png_ptr, info_ptr, &mod_time); | 1223 | png_get_tIME(png_ptr, info_ptr, &mod_time); |
1224 | 1224 | ||
1225 | mod_time - time image was last modified | 1225 | mod_time - time image was last modified |
1226 | (PNG_VALID_tIME) | 1226 | (PNG_VALID_tIME) |
1227 | 1227 | ||
1228 | png_get_bKGD(png_ptr, info_ptr, &background); | 1228 | png_get_bKGD(png_ptr, info_ptr, &background); |
1229 | 1229 | ||
1230 | background - background color (of type | 1230 | background - background color (of type |
1231 | png_color_16p) (PNG_VALID_bKGD) | 1231 | png_color_16p) (PNG_VALID_bKGD) |
1232 | valid 16-bit red, green and blue | 1232 | valid 16-bit red, green and blue |
1233 | values, regardless of color_type | 1233 | values, regardless of color_type |
1234 | 1234 | ||
1235 | num_comments = png_get_text(png_ptr, info_ptr, | 1235 | num_comments = png_get_text(png_ptr, info_ptr, |
1236 | &text_ptr, &num_text); | 1236 | &text_ptr, &num_text); |
1237 | 1237 | ||
1238 | num_comments - number of comments | 1238 | num_comments - number of comments |
1239 | 1239 | ||
1240 | text_ptr - array of png_text holding image | 1240 | text_ptr - array of png_text holding image |
1241 | comments | 1241 | comments |
1242 | 1242 | ||
1243 | text_ptr[i].compression - type of compression used | 1243 | text_ptr[i].compression - type of compression used |
1244 | on "text" PNG_TEXT_COMPRESSION_NONE | 1244 | on "text" PNG_TEXT_COMPRESSION_NONE |
1245 | PNG_TEXT_COMPRESSION_zTXt | 1245 | PNG_TEXT_COMPRESSION_zTXt |
1246 | PNG_ITXT_COMPRESSION_NONE | 1246 | PNG_ITXT_COMPRESSION_NONE |
1247 | PNG_ITXT_COMPRESSION_zTXt | 1247 | PNG_ITXT_COMPRESSION_zTXt |
1248 | 1248 | ||
1249 | text_ptr[i].key - keyword for comment. Must contain | 1249 | text_ptr[i].key - keyword for comment. Must contain |
1250 | 1-79 characters. | 1250 | 1-79 characters. |
1251 | 1251 | ||
1252 | text_ptr[i].text - text comments for current | 1252 | text_ptr[i].text - text comments for current |
1253 | keyword. Can be empty. | 1253 | keyword. Can be empty. |
1254 | 1254 | ||
1255 | text_ptr[i].text_length - length of text string, | 1255 | text_ptr[i].text_length - length of text string, |
1256 | after decompression, 0 for iTXt | 1256 | after decompression, 0 for iTXt |
1257 | 1257 | ||
1258 | text_ptr[i].itxt_length - length of itxt string, | 1258 | text_ptr[i].itxt_length - length of itxt string, |
1259 | after decompression, 0 for tEXt/zTXt | 1259 | after decompression, 0 for tEXt/zTXt |
1260 | 1260 | ||
1261 | text_ptr[i].lang - language of comment (empty | 1261 | text_ptr[i].lang - language of comment (empty |
1262 | string for unknown). | 1262 | string for unknown). |
1263 | 1263 | ||
1264 | text_ptr[i].lang_key - keyword in UTF-8 | 1264 | text_ptr[i].lang_key - keyword in UTF-8 |
1265 | (empty string for unknown). | 1265 | (empty string for unknown). |
1266 | 1266 | ||
1267 | Note that the itxt_length, lang, and lang_key | 1267 | Note that the itxt_length, lang, and lang_key |
1268 | members of the text_ptr structure only exist when the | 1268 | members of the text_ptr structure only exist when the |
1269 | library is built with iTXt chunk support. Prior to | 1269 | library is built with iTXt chunk support. Prior to |
1270 | libpng-1.4.0 the library was built by default without | 1270 | libpng-1.4.0 the library was built by default without |
1271 | iTXt support. Also note that when iTXt is supported, | 1271 | iTXt support. Also note that when iTXt is supported, |
1272 | they contain NULL pointers when the "compression" | 1272 | they contain NULL pointers when the "compression" |
1273 | field contains PNG_TEXT_COMPRESSION_NONE or | 1273 | field contains PNG_TEXT_COMPRESSION_NONE or |
1274 | PNG_TEXT_COMPRESSION_zTXt. | 1274 | PNG_TEXT_COMPRESSION_zTXt. |
1275 | 1275 | ||
1276 | num_text - number of comments (same as | 1276 | num_text - number of comments (same as |
1277 | num_comments; you can put NULL here | 1277 | num_comments; you can put NULL here |
1278 | to avoid the duplication) | 1278 | to avoid the duplication) |
1279 | 1279 | ||
1280 | Note while png_set_text() will accept text, language, | 1280 | Note while png_set_text() will accept text, language, |
1281 | and translated keywords that can be NULL pointers, the | 1281 | and translated keywords that can be NULL pointers, the |
1282 | structure returned by png_get_text will always contain | 1282 | structure returned by png_get_text will always contain |
1283 | regular zero-terminated C strings. They might be | 1283 | regular zero-terminated C strings. They might be |
1284 | empty strings but they will never be NULL pointers. | 1284 | empty strings but they will never be NULL pointers. |
1285 | 1285 | ||
1286 | num_spalettes = png_get_sPLT(png_ptr, info_ptr, | 1286 | num_spalettes = png_get_sPLT(png_ptr, info_ptr, |
1287 | &palette_ptr); | 1287 | &palette_ptr); |
1288 | 1288 | ||
1289 | num_spalettes - number of sPLT chunks read. | 1289 | num_spalettes - number of sPLT chunks read. |
1290 | 1290 | ||
1291 | palette_ptr - array of palette structures holding | 1291 | palette_ptr - array of palette structures holding |
1292 | contents of one or more sPLT chunks | 1292 | contents of one or more sPLT chunks |
1293 | read. | 1293 | read. |
1294 | 1294 | ||
1295 | png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y, | 1295 | png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y, |
1296 | &unit_type); | 1296 | &unit_type); |
1297 | 1297 | ||
1298 | offset_x - positive offset from the left edge | 1298 | offset_x - positive offset from the left edge |
1299 | of the screen (can be negative) | 1299 | of the screen (can be negative) |
1300 | 1300 | ||
1301 | offset_y - positive offset from the top edge | 1301 | offset_y - positive offset from the top edge |
1302 | of the screen (can be negative) | 1302 | of the screen (can be negative) |
1303 | 1303 | ||
1304 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER | 1304 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER |
1305 | 1305 | ||
1306 | png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y, | 1306 | png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y, |
1307 | &unit_type); | 1307 | &unit_type); |
1308 | 1308 | ||
1309 | res_x - pixels/unit physical resolution in | 1309 | res_x - pixels/unit physical resolution in |
1310 | x direction | 1310 | x direction |
1311 | 1311 | ||
1312 | res_y - pixels/unit physical resolution in | 1312 | res_y - pixels/unit physical resolution in |
1313 | x direction | 1313 | x direction |
1314 | 1314 | ||
1315 | unit_type - PNG_RESOLUTION_UNKNOWN, | 1315 | unit_type - PNG_RESOLUTION_UNKNOWN, |
1316 | PNG_RESOLUTION_METER | 1316 | PNG_RESOLUTION_METER |
1317 | 1317 | ||
1318 | png_get_sCAL(png_ptr, info_ptr, &unit, &width, | 1318 | png_get_sCAL(png_ptr, info_ptr, &unit, &width, |
1319 | &height) | 1319 | &height) |
1320 | 1320 | ||
1321 | unit - physical scale units (an integer) | 1321 | unit - physical scale units (an integer) |
1322 | 1322 | ||
1323 | width - width of a pixel in physical scale units | 1323 | width - width of a pixel in physical scale units |
1324 | 1324 | ||
1325 | height - height of a pixel in physical scale units | 1325 | height - height of a pixel in physical scale units |
1326 | (width and height are doubles) | 1326 | (width and height are doubles) |
1327 | 1327 | ||
1328 | png_get_sCAL_s(png_ptr, info_ptr, &unit, &width, | 1328 | png_get_sCAL_s(png_ptr, info_ptr, &unit, &width, |
1329 | &height) | 1329 | &height) |
1330 | 1330 | ||
1331 | unit - physical scale units (an integer) | 1331 | unit - physical scale units (an integer) |
1332 | 1332 | ||
1333 | width - width of a pixel in physical scale units | 1333 | width - width of a pixel in physical scale units |
1334 | (expressed as a string) | 1334 | (expressed as a string) |
1335 | 1335 | ||
1336 | height - height of a pixel in physical scale units | 1336 | height - height of a pixel in physical scale units |
1337 | (width and height are strings like "2.54") | 1337 | (width and height are strings like "2.54") |
1338 | 1338 | ||
1339 | num_unknown_chunks = png_get_unknown_chunks(png_ptr, | 1339 | num_unknown_chunks = png_get_unknown_chunks(png_ptr, |
1340 | info_ptr, &unknowns) | 1340 | info_ptr, &unknowns) |
1341 | 1341 | ||
1342 | unknowns - array of png_unknown_chunk | 1342 | unknowns - array of png_unknown_chunk |
1343 | structures holding unknown chunks | 1343 | structures holding unknown chunks |
1344 | 1344 | ||
1345 | unknowns[i].name - name of unknown chunk | 1345 | unknowns[i].name - name of unknown chunk |
1346 | 1346 | ||
1347 | unknowns[i].data - data of unknown chunk | 1347 | unknowns[i].data - data of unknown chunk |
1348 | 1348 | ||
1349 | unknowns[i].size - size of unknown chunk's data | 1349 | unknowns[i].size - size of unknown chunk's data |
1350 | 1350 | ||
1351 | unknowns[i].location - position of chunk in file | 1351 | unknowns[i].location - position of chunk in file |
1352 | 1352 | ||
1353 | The value of "i" corresponds to the order in which the | 1353 | The value of "i" corresponds to the order in which the |
1354 | chunks were read from the PNG file or inserted with the | 1354 | chunks were read from the PNG file or inserted with the |
1355 | png_set_unknown_chunks() function. | 1355 | png_set_unknown_chunks() function. |
1356 | 1356 | ||
1357 | The value of "location" is a bitwise "or" of | 1357 | The value of "location" is a bitwise "or" of |
1358 | 1358 | ||
1359 | PNG_HAVE_IHDR (0x01) | 1359 | PNG_HAVE_IHDR (0x01) |
1360 | PNG_HAVE_PLTE (0x02) | 1360 | PNG_HAVE_PLTE (0x02) |
1361 | PNG_AFTER_IDAT (0x08) | 1361 | PNG_AFTER_IDAT (0x08) |
1362 | 1362 | ||
1363 | The data from the pHYs chunk can be retrieved in several convenient | 1363 | The data from the pHYs chunk can be retrieved in several convenient |
1364 | forms: | 1364 | forms: |
1365 | 1365 | ||
1366 | res_x = png_get_x_pixels_per_meter(png_ptr, | 1366 | res_x = png_get_x_pixels_per_meter(png_ptr, |
1367 | info_ptr) | 1367 | info_ptr) |
1368 | 1368 | ||
1369 | res_y = png_get_y_pixels_per_meter(png_ptr, | 1369 | res_y = png_get_y_pixels_per_meter(png_ptr, |
1370 | info_ptr) | 1370 | info_ptr) |
1371 | 1371 | ||
1372 | res_x_and_y = png_get_pixels_per_meter(png_ptr, | 1372 | res_x_and_y = png_get_pixels_per_meter(png_ptr, |
1373 | info_ptr) | 1373 | info_ptr) |
1374 | 1374 | ||
1375 | res_x = png_get_x_pixels_per_inch(png_ptr, | 1375 | res_x = png_get_x_pixels_per_inch(png_ptr, |
1376 | info_ptr) | 1376 | info_ptr) |
1377 | 1377 | ||
1378 | res_y = png_get_y_pixels_per_inch(png_ptr, | 1378 | res_y = png_get_y_pixels_per_inch(png_ptr, |
1379 | info_ptr) | 1379 | info_ptr) |
1380 | 1380 | ||
1381 | res_x_and_y = png_get_pixels_per_inch(png_ptr, | 1381 | res_x_and_y = png_get_pixels_per_inch(png_ptr, |
1382 | info_ptr) | 1382 | info_ptr) |
1383 | 1383 | ||
1384 | aspect_ratio = png_get_pixel_aspect_ratio(png_ptr, | 1384 | aspect_ratio = png_get_pixel_aspect_ratio(png_ptr, |
1385 | info_ptr) | 1385 | info_ptr) |
1386 | 1386 | ||
1387 | Each of these returns 0 [signifying "unknown"] if | 1387 | Each of these returns 0 [signifying "unknown"] if |
1388 | the data is not present or if res_x is 0; | 1388 | the data is not present or if res_x is 0; |
1389 | res_x_and_y is 0 if res_x != res_y | 1389 | res_x_and_y is 0 if res_x != res_y |
1390 | 1390 | ||
1391 | Note that because of the way the resolutions are | 1391 | Note that because of the way the resolutions are |
1392 | stored internally, the inch conversions won't | 1392 | stored internally, the inch conversions won't |
1393 | come out to exactly even number. For example, | 1393 | come out to exactly even number. For example, |
1394 | 72 dpi is stored as 0.28346 pixels/meter, and | 1394 | 72 dpi is stored as 0.28346 pixels/meter, and |
1395 | when this is retrieved it is 71.9988 dpi, so | 1395 | when this is retrieved it is 71.9988 dpi, so |
1396 | be sure to round the returned value appropriately | 1396 | be sure to round the returned value appropriately |
1397 | if you want to display a reasonable-looking result. | 1397 | if you want to display a reasonable-looking result. |
1398 | 1398 | ||
1399 | The data from the oFFs chunk can be retrieved in several convenient | 1399 | The data from the oFFs chunk can be retrieved in several convenient |
1400 | forms: | 1400 | forms: |
1401 | 1401 | ||
1402 | x_offset = png_get_x_offset_microns(png_ptr, info_ptr); | 1402 | x_offset = png_get_x_offset_microns(png_ptr, info_ptr); |
1403 | 1403 | ||
1404 | y_offset = png_get_y_offset_microns(png_ptr, info_ptr); | 1404 | y_offset = png_get_y_offset_microns(png_ptr, info_ptr); |
1405 | 1405 | ||
1406 | x_offset = png_get_x_offset_inches(png_ptr, info_ptr); | 1406 | x_offset = png_get_x_offset_inches(png_ptr, info_ptr); |
1407 | 1407 | ||
1408 | y_offset = png_get_y_offset_inches(png_ptr, info_ptr); | 1408 | y_offset = png_get_y_offset_inches(png_ptr, info_ptr); |
1409 | 1409 | ||
1410 | Each of these returns 0 [signifying "unknown" if both | 1410 | Each of these returns 0 [signifying "unknown" if both |
1411 | x and y are 0] if the data is not present or if the | 1411 | x and y are 0] if the data is not present or if the |
1412 | chunk is present but the unit is the pixel. The | 1412 | chunk is present but the unit is the pixel. The |
1413 | remark about inexact inch conversions applies here | 1413 | remark about inexact inch conversions applies here |
1414 | as well, because a value in inches can't always be | 1414 | as well, because a value in inches can't always be |
1415 | converted to microns and back without some loss | 1415 | converted to microns and back without some loss |
1416 | of precision. | 1416 | of precision. |
1417 | 1417 | ||
1418 | For more information, see the | 1418 | For more information, see the |
1419 | PNG specification for chunk contents. Be careful with trusting | 1419 | PNG specification for chunk contents. Be careful with trusting |
1420 | rowbytes, as some of the transformations could increase the space | 1420 | rowbytes, as some of the transformations could increase the space |
1421 | needed to hold a row (expand, filler, gray_to_rgb, etc.). | 1421 | needed to hold a row (expand, filler, gray_to_rgb, etc.). |
1422 | See png_read_update_info(), below. | 1422 | See png_read_update_info(), below. |
1423 | 1423 | ||
1424 | A quick word about text_ptr and num_text. PNG stores comments in | 1424 | A quick word about text_ptr and num_text. PNG stores comments in |
1425 | keyword/text pairs, one pair per chunk, with no limit on the number | 1425 | keyword/text pairs, one pair per chunk, with no limit on the number |
1426 | of text chunks, and a 2^31 byte limit on their size. While there are | 1426 | of text chunks, and a 2^31 byte limit on their size. While there are |
1427 | suggested keywords, there is no requirement to restrict the use to these | 1427 | suggested keywords, there is no requirement to restrict the use to these |
1428 | strings. It is strongly suggested that keywords and text be sensible | 1428 | strings. It is strongly suggested that keywords and text be sensible |
1429 | to humans (that's the point), so don't use abbreviations. Non-printing | 1429 | to humans (that's the point), so don't use abbreviations. Non-printing |
1430 | symbols are not allowed. See the PNG specification for more details. | 1430 | symbols are not allowed. See the PNG specification for more details. |
1431 | There is also no requirement to have text after the keyword. | 1431 | There is also no requirement to have text after the keyword. |
1432 | 1432 | ||
1433 | Keywords should be limited to 79 Latin-1 characters without leading or | 1433 | Keywords should be limited to 79 Latin-1 characters without leading or |
1434 | trailing spaces, but non-consecutive spaces are allowed within the | 1434 | trailing spaces, but non-consecutive spaces are allowed within the |
1435 | keyword. It is possible to have the same keyword any number of times. | 1435 | keyword. It is possible to have the same keyword any number of times. |
1436 | The text_ptr is an array of png_text structures, each holding a | 1436 | The text_ptr is an array of png_text structures, each holding a |
1437 | pointer to a language string, a pointer to a keyword and a pointer to | 1437 | pointer to a language string, a pointer to a keyword and a pointer to |
1438 | a text string. The text string, language code, and translated | 1438 | a text string. The text string, language code, and translated |
1439 | keyword may be empty or NULL pointers. The keyword/text | 1439 | keyword may be empty or NULL pointers. The keyword/text |
1440 | pairs are put into the array in the order that they are received. | 1440 | pairs are put into the array in the order that they are received. |
1441 | However, some or all of the text chunks may be after the image, so, to | 1441 | However, some or all of the text chunks may be after the image, so, to |
1442 | make sure you have read all the text chunks, don't mess with these | 1442 | make sure you have read all the text chunks, don't mess with these |
1443 | until after you read the stuff after the image. This will be | 1443 | until after you read the stuff after the image. This will be |
1444 | mentioned again below in the discussion that goes with png_read_end(). | 1444 | mentioned again below in the discussion that goes with png_read_end(). |
1445 | 1445 | ||
1446 | Input transformations | 1446 | Input transformations |
1447 | 1447 | ||
1448 | After you've read the header information, you can set up the library | 1448 | After you've read the header information, you can set up the library |
1449 | to handle any special transformations of the image data. The various | 1449 | to handle any special transformations of the image data. The various |
1450 | ways to transform the data will be described in the order that they | 1450 | ways to transform the data will be described in the order that they |
1451 | should occur. This is important, as some of these change the color | 1451 | should occur. This is important, as some of these change the color |
1452 | type and/or bit depth of the data, and some others only work on | 1452 | type and/or bit depth of the data, and some others only work on |
1453 | certain color types and bit depths. | 1453 | certain color types and bit depths. |
1454 | 1454 | ||
1455 | Transformations you request are ignored if they don't have any meaning for a | 1455 | Transformations you request are ignored if they don't have any meaning for a |
1456 | particular input data format. However some transformations can have an effect | 1456 | particular input data format. However some transformations can have an effect |
1457 | as a result of a previous transformation. If you specify a contradictory set of | 1457 | as a result of a previous transformation. If you specify a contradictory set of |
1458 | transformations, for example both adding and removing the alpha channel, you | 1458 | transformations, for example both adding and removing the alpha channel, you |
1459 | cannot predict the final result. | 1459 | cannot predict the final result. |
1460 | 1460 | ||
1461 | The color used for the transparency values should be supplied in the same | 1461 | The color used for the transparency values should be supplied in the same |
1462 | format/depth as the current image data. It is stored in the same format/depth | 1462 | format/depth as the current image data. It is stored in the same format/depth |
1463 | as the image data in a tRNS chunk, so this is what libpng expects for this data. | 1463 | as the image data in a tRNS chunk, so this is what libpng expects for this data. |
1464 | 1464 | ||
1465 | The color used for the background value depends on the need_expand argument as | 1465 | The color used for the background value depends on the need_expand argument as |
1466 | described below. | 1466 | described below. |
1467 | 1467 | ||
1468 | Data will be decoded into the supplied row buffers packed into bytes | 1468 | Data will be decoded into the supplied row buffers packed into bytes |
1469 | unless the library has been told to transform it into another format. | 1469 | unless the library has been told to transform it into another format. |
1470 | For example, 4 bit/pixel paletted or grayscale data will be returned | 1470 | For example, 4 bit/pixel paletted or grayscale data will be returned |
1471 | 2 pixels/byte with the leftmost pixel in the high-order bits of the | 1471 | 2 pixels/byte with the leftmost pixel in the high-order bits of the |
1472 | byte, unless png_set_packing() is called. 8-bit RGB data will be stored | 1472 | byte, unless png_set_packing() is called. 8-bit RGB data will be stored |
1473 | in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha() | 1473 | in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha() |
1474 | is called to insert filler bytes, either before or after each RGB triplet. | 1474 | is called to insert filler bytes, either before or after each RGB triplet. |
1475 | 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant | 1475 | 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant |
1476 | byte of the color value first, unless png_set_scale_16() is called to | 1476 | byte of the color value first, unless png_set_scale_16() is called to |
1477 | transform it to regular RGB RGB triplets, or png_set_filler() or | 1477 | transform it to regular RGB RGB triplets, or png_set_filler() or |
1478 | png_set_add alpha() is called to insert filler bytes, either before or | 1478 | png_set_add alpha() is called to insert filler bytes, either before or |
1479 | after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can | 1479 | after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can |
1480 | be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(), | 1480 | be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(), |
1481 | or png_set_scale_16(). | 1481 | or png_set_scale_16(). |
1482 | 1482 | ||
1483 | The following code transforms grayscale images of less than 8 to 8 bits, | 1483 | The following code transforms grayscale images of less than 8 to 8 bits, |
1484 | changes paletted images to RGB, and adds a full alpha channel if there is | 1484 | changes paletted images to RGB, and adds a full alpha channel if there is |
1485 | transparency information in a tRNS chunk. This is most useful on | 1485 | transparency information in a tRNS chunk. This is most useful on |
1486 | grayscale images with bit depths of 2 or 4 or if there is a multiple-image | 1486 | grayscale images with bit depths of 2 or 4 or if there is a multiple-image |
1487 | viewing application that wishes to treat all images in the same way. | 1487 | viewing application that wishes to treat all images in the same way. |
1488 | 1488 | ||
1489 | if (color_type == PNG_COLOR_TYPE_PALETTE) | 1489 | if (color_type == PNG_COLOR_TYPE_PALETTE) |
1490 | png_set_palette_to_rgb(png_ptr); | 1490 | png_set_palette_to_rgb(png_ptr); |
1491 | 1491 | ||
1492 | if (png_get_valid(png_ptr, info_ptr, | 1492 | if (png_get_valid(png_ptr, info_ptr, |
1493 | PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr); | 1493 | PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr); |
1494 | 1494 | ||
1495 | if (color_type == PNG_COLOR_TYPE_GRAY && | 1495 | if (color_type == PNG_COLOR_TYPE_GRAY && |
1496 | bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr); | 1496 | bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr); |
1497 | 1497 | ||
1498 | The first two functions are actually aliases for png_set_expand(), added | 1498 | The first two functions are actually aliases for png_set_expand(), added |
1499 | in libpng version 1.0.4, with the function names expanded to improve code | 1499 | in libpng version 1.0.4, with the function names expanded to improve code |
1500 | readability. In some future version they may actually do different | 1500 | readability. In some future version they may actually do different |
1501 | things. | 1501 | things. |
1502 | 1502 | ||
1503 | As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was | 1503 | As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was |
1504 | added. It expands the sample depth without changing tRNS to alpha. | 1504 | added. It expands the sample depth without changing tRNS to alpha. |
1505 | 1505 | ||
1506 | As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as | 1506 | As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as |
1507 | png_set_expand(); however, the resultant channels have 16 bits rather than 8. | 1507 | png_set_expand(); however, the resultant channels have 16 bits rather than 8. |
1508 | Use this when the output color or gray channels are made linear to avoid fairly | 1508 | Use this when the output color or gray channels are made linear to avoid fairly |
1509 | severe accuracy loss. | 1509 | severe accuracy loss. |
1510 | 1510 | ||
1511 | if (bit_depth < 16) | 1511 | if (bit_depth < 16) |
1512 | png_set_expand_16(png_ptr); | 1512 | png_set_expand_16(png_ptr); |
1513 | 1513 | ||
1514 | PNG can have files with 16 bits per channel. If you only can handle | 1514 | PNG can have files with 16 bits per channel. If you only can handle |
1515 | 8 bits per channel, this will strip the pixels down to 8-bit. | 1515 | 8 bits per channel, this will strip the pixels down to 8-bit. |
1516 | 1516 | ||
1517 | if (bit_depth == 16) | 1517 | if (bit_depth == 16) |
1518 | #if PNG_LIBPNG_VER >= 10504 | 1518 | #if PNG_LIBPNG_VER >= 10504 |
1519 | png_set_scale_16(png_ptr); | 1519 | png_set_scale_16(png_ptr); |
1520 | #else | 1520 | #else |
1521 | png_set_strip_16(png_ptr); | 1521 | png_set_strip_16(png_ptr); |
1522 | #endif | 1522 | #endif |
1523 | 1523 | ||
1524 | (The more accurate "png_set_scale_16()" API became available in libpng version | 1524 | (The more accurate "png_set_scale_16()" API became available in libpng version |
1525 | 1.5.4). | 1525 | 1.5.4). |
1526 | 1526 | ||
1527 | If you need to process the alpha channel on the image separately from the image | 1527 | If you need to process the alpha channel on the image separately from the image |
1528 | data (for example if you convert it to a bitmap mask) it is possible to have | 1528 | data (for example if you convert it to a bitmap mask) it is possible to have |
1529 | libpng strip the channel leaving just RGB or gray data: | 1529 | libpng strip the channel leaving just RGB or gray data: |
1530 | 1530 | ||
1531 | if (color_type & PNG_COLOR_MASK_ALPHA) | 1531 | if (color_type & PNG_COLOR_MASK_ALPHA) |
1532 | png_set_strip_alpha(png_ptr); | 1532 | png_set_strip_alpha(png_ptr); |
1533 | 1533 | ||
1534 | If you strip the alpha channel you need to find some other way of dealing with | 1534 | If you strip the alpha channel you need to find some other way of dealing with |
1535 | the information. If, instead, you want to convert the image to an opaque | 1535 | the information. If, instead, you want to convert the image to an opaque |
1536 | version with no alpha channel use png_set_background; see below. | 1536 | version with no alpha channel use png_set_background; see below. |
1537 | 1537 | ||
1538 | As of libpng version 1.5.2, almost all useful expansions are supported, the | 1538 | As of libpng version 1.5.2, almost all useful expansions are supported, the |
1539 | major ommissions are conversion of grayscale to indexed images (which can be | 1539 | major ommissions are conversion of grayscale to indexed images (which can be |
1540 | done trivially in the application) and conversion of indexed to grayscale (which | 1540 | done trivially in the application) and conversion of indexed to grayscale (which |
1541 | can be done by a trivial manipulation of the palette.) | 1541 | can be done by a trivial manipulation of the palette.) |
1542 | 1542 | ||
1543 | In the following table, the 01 means grayscale with depth<8, 31 means | 1543 | In the following table, the 01 means grayscale with depth<8, 31 means |
1544 | indexed with depth<8, other numerals represent the color type, "T" means | 1544 | indexed with depth<8, other numerals represent the color type, "T" means |
1545 | the tRNS chunk is present, A means an alpha channel is present, and O | 1545 | the tRNS chunk is present, A means an alpha channel is present, and O |
1546 | means tRNS or alpha is present but all pixels in the image are opaque. | 1546 | means tRNS or alpha is present but all pixels in the image are opaque. |
1547 | 1547 | ||
1548 | FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O | 1548 | FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O |
1549 | TO | 1549 | TO |
1550 | 01 - [G] - - - - - - - - - - - - - | 1550 | 01 - [G] - - - - - - - - - - - - - |
1551 | 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q | 1551 | 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q |
1552 | 0 1 G + . . G G G G G G B B GB GB | 1552 | 0 1 G + . . G G G G G G B B GB GB |
1553 | 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt | 1553 | 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt |
1554 | 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt | 1554 | 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt |
1555 | 2 C P C C C + . . C - - CB CB B B | 1555 | 2 C P C C C + . . C - - CB CB B B |
1556 | 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt | 1556 | 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt |
1557 | 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt | 1557 | 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt |
1558 | 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q | 1558 | 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q |
1559 | 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt | 1559 | 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt |
1560 | 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt | 1560 | 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt |
1561 | 4A lA G A T T GA GT GT GA GT GT + BA G GBA | 1561 | 4A lA G A T T GA GT GT GA GT GT + BA G GBA |
1562 | 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G | 1562 | 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G |
1563 | 6A CA PA CA C C A T tT PA P P C CBA + BA | 1563 | 6A CA PA CA C C A T tT PA P P C CBA + BA |
1564 | 6O CA PBA CA C C A tT T PA P P CBA C BA + | 1564 | 6O CA PBA CA C C A tT T PA P P CBA C BA + |
1565 | 1565 | ||
1566 | Within the matrix, | 1566 | Within the matrix, |
1567 | "+" identifies entries where 'from' and 'to' are the same. | 1567 | "+" identifies entries where 'from' and 'to' are the same. |
1568 | "-" means the transformation is not supported. | 1568 | "-" means the transformation is not supported. |
1569 | "." means nothing is necessary (a tRNS chunk can just be ignored). | 1569 | "." means nothing is necessary (a tRNS chunk can just be ignored). |
1570 | "t" means the transformation is obtained by png_set_tRNS. | 1570 | "t" means the transformation is obtained by png_set_tRNS. |
1571 | "A" means the transformation is obtained by png_set_add_alpha(). | 1571 | "A" means the transformation is obtained by png_set_add_alpha(). |
1572 | "X" means the transformation is obtained by png_set_expand(). | 1572 | "X" means the transformation is obtained by png_set_expand(). |
1573 | "1" means the transformation is obtained by | 1573 | "1" means the transformation is obtained by |
1574 | png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there | 1574 | png_set_expand_gray_1_2_4_to_8() (and by png_set_expand() if there |
1575 | is no transparency in the original or the final format). | 1575 | is no transparency in the original or the final format). |
1576 | "C" means the transformation is obtained by png_set_gray_to_rgb(). | 1576 | "C" means the transformation is obtained by png_set_gray_to_rgb(). |
1577 | "G" means the transformation is obtained by png_set_rgb_to_gray(). | 1577 | "G" means the transformation is obtained by png_set_rgb_to_gray(). |
1578 | "P" means the transformation is obtained by | 1578 | "P" means the transformation is obtained by |
1579 | png_set_expand_palette_to_rgb(). | 1579 | png_set_expand_palette_to_rgb(). |
1580 | "p" means the transformation is obtained by png_set_packing(). | 1580 | "p" means the transformation is obtained by png_set_packing(). |
1581 | "Q" means the transformation is obtained by png_set_quantize(). | 1581 | "Q" means the transformation is obtained by png_set_quantize(). |
1582 | "T" means the transformation is obtained by png_set_tRNS_to_alpha(). | 1582 | "T" means the transformation is obtained by png_set_tRNS_to_alpha(). |
1583 | "B" means the transformation is obtained by png_set_background(), or | 1583 | "B" means the transformation is obtained by png_set_background(), or |
1584 | png_strip_alpha(). | 1584 | png_strip_alpha(). |
1585 | 1585 | ||
1586 | When an entry has multiple transforms listed all are required to cause the | 1586 | When an entry has multiple transforms listed all are required to cause the |
1587 | right overall transformation. When two transforms are separated by a comma | 1587 | right overall transformation. When two transforms are separated by a comma |
1588 | either will do the job. When transforms are enclosed in [] the transform should | 1588 | either will do the job. When transforms are enclosed in [] the transform should |
1589 | do the job but this is currently unimplemented - a different format will result | 1589 | do the job but this is currently unimplemented - a different format will result |
1590 | if the suggested transformations are used. | 1590 | if the suggested transformations are used. |
1591 | 1591 | ||
1592 | In PNG files, the alpha channel in an image | 1592 | In PNG files, the alpha channel in an image |
1593 | is the level of opacity. If you need the alpha channel in an image to | 1593 | is the level of opacity. If you need the alpha channel in an image to |
1594 | be the level of transparency instead of opacity, you can invert the | 1594 | be the level of transparency instead of opacity, you can invert the |
1595 | alpha channel (or the tRNS chunk data) after it's read, so that 0 is | 1595 | alpha channel (or the tRNS chunk data) after it's read, so that 0 is |
1596 | fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit | 1596 | fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit |
1597 | images) is fully transparent, with | 1597 | images) is fully transparent, with |
1598 | 1598 | ||
1599 | png_set_invert_alpha(png_ptr); | 1599 | png_set_invert_alpha(png_ptr); |
1600 | 1600 | ||
1601 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as | 1601 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as |
1602 | they can, resulting in, for example, 8 pixels per byte for 1 bit | 1602 | they can, resulting in, for example, 8 pixels per byte for 1 bit |
1603 | files. This code expands to 1 pixel per byte without changing the | 1603 | files. This code expands to 1 pixel per byte without changing the |
1604 | values of the pixels: | 1604 | values of the pixels: |
1605 | 1605 | ||
1606 | if (bit_depth < 8) | 1606 | if (bit_depth < 8) |
1607 | png_set_packing(png_ptr); | 1607 | png_set_packing(png_ptr); |
1608 | 1608 | ||
1609 | PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels | 1609 | PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels |
1610 | stored in a PNG image have been "scaled" or "shifted" up to the next | 1610 | stored in a PNG image have been "scaled" or "shifted" up to the next |
1611 | higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] | 1611 | higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] |
1612 | to 8 bits/sample in the range [0, 255]). However, it is also possible | 1612 | to 8 bits/sample in the range [0, 255]). However, it is also possible |
1613 | to convert the PNG pixel data back to the original bit depth of the | 1613 | to convert the PNG pixel data back to the original bit depth of the |
1614 | image. This call reduces the pixels back down to the original bit depth: | 1614 | image. This call reduces the pixels back down to the original bit depth: |
1615 | 1615 | ||
1616 | png_color_8p sig_bit; | 1616 | png_color_8p sig_bit; |
1617 | 1617 | ||
1618 | if (png_get_sBIT(png_ptr, info_ptr, &sig_bit)) | 1618 | if (png_get_sBIT(png_ptr, info_ptr, &sig_bit)) |
1619 | png_set_shift(png_ptr, sig_bit); | 1619 | png_set_shift(png_ptr, sig_bit); |
1620 | 1620 | ||
1621 | PNG files store 3-color pixels in red, green, blue order. This code | 1621 | PNG files store 3-color pixels in red, green, blue order. This code |
1622 | changes the storage of the pixels to blue, green, red: | 1622 | changes the storage of the pixels to blue, green, red: |
1623 | 1623 | ||
1624 | if (color_type == PNG_COLOR_TYPE_RGB || | 1624 | if (color_type == PNG_COLOR_TYPE_RGB || |
1625 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) | 1625 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) |
1626 | png_set_bgr(png_ptr); | 1626 | png_set_bgr(png_ptr); |
1627 | 1627 | ||
1628 | PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them | 1628 | PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them |
1629 | into 4 or 8 bytes for windowing systems that need them in this format: | 1629 | into 4 or 8 bytes for windowing systems that need them in this format: |
1630 | 1630 | ||
1631 | if (color_type == PNG_COLOR_TYPE_RGB) | 1631 | if (color_type == PNG_COLOR_TYPE_RGB) |
1632 | png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE); | 1632 | png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE); |
1633 | 1633 | ||
1634 | where "filler" is the 8 or 16-bit number to fill with, and the location is | 1634 | where "filler" is the 8 or 16-bit number to fill with, and the location is |
1635 | either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether | 1635 | either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether |
1636 | you want the filler before the RGB or after. This transformation | 1636 | you want the filler before the RGB or after. This transformation |
1637 | does not affect images that already have full alpha channels. To add an | 1637 | does not affect images that already have full alpha channels. To add an |
1638 | opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which | 1638 | opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which |
1639 | will generate RGBA pixels. | 1639 | will generate RGBA pixels. |
1640 | 1640 | ||
1641 | Note that png_set_filler() does not change the color type. If you want | 1641 | Note that png_set_filler() does not change the color type. If you want |
1642 | to do that, you can add a true alpha channel with | 1642 | to do that, you can add a true alpha channel with |
1643 | 1643 | ||
1644 | if (color_type == PNG_COLOR_TYPE_RGB || | 1644 | if (color_type == PNG_COLOR_TYPE_RGB || |
1645 | color_type == PNG_COLOR_TYPE_GRAY) | 1645 | color_type == PNG_COLOR_TYPE_GRAY) |
1646 | png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER); | 1646 | png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER); |
1647 | 1647 | ||
1648 | where "filler" contains the alpha value to assign to each pixel. | 1648 | where "filler" contains the alpha value to assign to each pixel. |
1649 | This function was added in libpng-1.2.7. | 1649 | This function was added in libpng-1.2.7. |
1650 | 1650 | ||
1651 | If you are reading an image with an alpha channel, and you need the | 1651 | If you are reading an image with an alpha channel, and you need the |
1652 | data as ARGB instead of the normal PNG format RGBA: | 1652 | data as ARGB instead of the normal PNG format RGBA: |
1653 | 1653 | ||
1654 | if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) | 1654 | if (color_type == PNG_COLOR_TYPE_RGB_ALPHA) |
1655 | png_set_swap_alpha(png_ptr); | 1655 | png_set_swap_alpha(png_ptr); |
1656 | 1656 | ||
1657 | For some uses, you may want a grayscale image to be represented as | 1657 | For some uses, you may want a grayscale image to be represented as |
1658 | RGB. This code will do that conversion: | 1658 | RGB. This code will do that conversion: |
1659 | 1659 | ||
1660 | if (color_type == PNG_COLOR_TYPE_GRAY || | 1660 | if (color_type == PNG_COLOR_TYPE_GRAY || |
1661 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | 1661 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) |
1662 | png_set_gray_to_rgb(png_ptr); | 1662 | png_set_gray_to_rgb(png_ptr); |
1663 | 1663 | ||
1664 | Conversely, you can convert an RGB or RGBA image to grayscale or grayscale | 1664 | Conversely, you can convert an RGB or RGBA image to grayscale or grayscale |
1665 | with alpha. | 1665 | with alpha. |
1666 | 1666 | ||
1667 | if (color_type == PNG_COLOR_TYPE_RGB || | 1667 | if (color_type == PNG_COLOR_TYPE_RGB || |
1668 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) | 1668 | color_type == PNG_COLOR_TYPE_RGB_ALPHA) |
1669 | png_set_rgb_to_gray(png_ptr, error_action, double red_weight, | 1669 | png_set_rgb_to_gray(png_ptr, error_action, double red_weight, |
1670 | double green_weight); | 1670 | double green_weight); |
1671 | 1671 | ||
1672 | error_action = 1: silently do the conversion | 1672 | error_action = 1: silently do the conversion |
1673 | 1673 | ||
1674 | error_action = 2: issue a warning if the original | 1674 | error_action = 2: issue a warning if the original |
1675 | image has any pixel where | 1675 | image has any pixel where |
1676 | red != green or red != blue | 1676 | red != green or red != blue |
1677 | 1677 | ||
1678 | error_action = 3: issue an error and abort the | 1678 | error_action = 3: issue an error and abort the |
1679 | conversion if the original | 1679 | conversion if the original |
1680 | image has any pixel where | 1680 | image has any pixel where |
1681 | red != green or red != blue | 1681 | red != green or red != blue |
1682 | 1682 | ||
1683 | red_weight: weight of red component | 1683 | red_weight: weight of red component |
1684 | 1684 | ||
1685 | green_weight: weight of green component | 1685 | green_weight: weight of green component |
1686 | If either weight is negative, default | 1686 | If either weight is negative, default |
1687 | weights are used. | 1687 | weights are used. |
1688 | 1688 | ||
1689 | In the corresponding fixed point API the red_weight and green_weight values are | 1689 | In the corresponding fixed point API the red_weight and green_weight values are |
1690 | simply scaled by 100,000: | 1690 | simply scaled by 100,000: |
1691 | 1691 | ||
1692 | png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight, | 1692 | png_set_rgb_to_gray(png_ptr, error_action, png_fixed_point red_weight, |
1693 | png_fixed_point green_weight); | 1693 | png_fixed_point green_weight); |
1694 | 1694 | ||
1695 | If you have set error_action = 1 or 2, you can | 1695 | If you have set error_action = 1 or 2, you can |
1696 | later check whether the image really was gray, after processing | 1696 | later check whether the image really was gray, after processing |
1697 | the image rows, with the png_get_rgb_to_gray_status(png_ptr) function. | 1697 | the image rows, with the png_get_rgb_to_gray_status(png_ptr) function. |
1698 | It will return a png_byte that is zero if the image was gray or | 1698 | It will return a png_byte that is zero if the image was gray or |
1699 | 1 if there were any non-gray pixels. Background and sBIT data | 1699 | 1 if there were any non-gray pixels. Background and sBIT data |
1700 | will be silently converted to grayscale, using the green channel | 1700 | will be silently converted to grayscale, using the green channel |
1701 | data for sBIT, regardless of the error_action setting. | 1701 | data for sBIT, regardless of the error_action setting. |
1702 | 1702 | ||
1703 | The default values come from the PNG file cHRM chunk if present; otherwise, the | 1703 | The default values come from the PNG file cHRM chunk if present; otherwise, the |
1704 | defaults correspond to the ITU-R recommendation 709, and also the sRGB color | 1704 | defaults correspond to the ITU-R recommendation 709, and also the sRGB color |
1705 | space, as recommended in the Charles Poynton's Colour FAQ, | 1705 | space, as recommended in the Charles Poynton's Colour FAQ, |
1706 | <http://www.poynton.com/>, in section 9: | 1706 | <http://www.poynton.com/>, in section 9: |
1707 | 1707 | ||
1708 | <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9> | 1708 | <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9> |
1709 | 1709 | ||
1710 | Y = 0.2126 * R + 0.7152 * G + 0.0722 * B | 1710 | Y = 0.2126 * R + 0.7152 * G + 0.0722 * B |
1711 | 1711 | ||
1712 | Previous versions of this document, 1998 through 2002, recommended a slightly | 1712 | Previous versions of this document, 1998 through 2002, recommended a slightly |
1713 | different formula: | 1713 | different formula: |
1714 | 1714 | ||
1715 | Y = 0.212671 * R + 0.715160 * G + 0.072169 * B | 1715 | Y = 0.212671 * R + 0.715160 * G + 0.072169 * B |
1716 | 1716 | ||
1717 | Libpng uses an integer approximation: | 1717 | Libpng uses an integer approximation: |
1718 | 1718 | ||
1719 | Y = (6968 * R + 23434 * G + 2366 * B)/32768 | 1719 | Y = (6968 * R + 23434 * G + 2366 * B)/32768 |
1720 | 1720 | ||
1721 | The calculation is done in a linear colorspace, if the image gamma | 1721 | The calculation is done in a linear colorspace, if the image gamma |
1722 | can be determined. | 1722 | can be determined. |
1723 | 1723 | ||
1724 | The png_set_background() function has been described already; it tells libpng to | 1724 | The png_set_background() function has been described already; it tells libpng to |
1725 | composite images with alpha or simple transparency against the supplied | 1725 | composite images with alpha or simple transparency against the supplied |
1726 | background color. For compatibility with versions of libpng earlier than | 1726 | background color. For compatibility with versions of libpng earlier than |
1727 | libpng-1.5.4 it is recommended that you call the function after reading the file | 1727 | libpng-1.5.4 it is recommended that you call the function after reading the file |
1728 | header, even if you don't want to use the color in a bKGD chunk, if one exists. | 1728 | header, even if you don't want to use the color in a bKGD chunk, if one exists. |
1729 | 1729 | ||
1730 | If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid), | 1730 | If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid), |
1731 | you may use this color, or supply another color more suitable for | 1731 | you may use this color, or supply another color more suitable for |
1732 | the current display (e.g., the background color from a web page). You | 1732 | the current display (e.g., the background color from a web page). You |
1733 | need to tell libpng how the color is represented, both the format of the | 1733 | need to tell libpng how the color is represented, both the format of the |
1734 | component values in the color (the number of bits) and the gamma encoding of the | 1734 | component values in the color (the number of bits) and the gamma encoding of the |
1735 | color. The function takes two arguments, background_gamma_mode and need_expand | 1735 | color. The function takes two arguments, background_gamma_mode and need_expand |
1736 | to convey this information, however only two combinations are likely to be | 1736 | to convey this information, however only two combinations are likely to be |
1737 | useful: | 1737 | useful: |
1738 | 1738 | ||
1739 | png_color_16 my_background; | 1739 | png_color_16 my_background; |
1740 | png_color_16p image_background; | 1740 | png_color_16p image_background; |
1741 | 1741 | ||
1742 | if (png_get_bKGD(png_ptr, info_ptr, &image_background)) | 1742 | if (png_get_bKGD(png_ptr, info_ptr, &image_background)) |
1743 | png_set_background(png_ptr, image_background, | 1743 | png_set_background(png_ptr, image_background, |
1744 | PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1); | 1744 | PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1); |
1745 | else | 1745 | else |
1746 | png_set_background(png_ptr, &my_background, | 1746 | png_set_background(png_ptr, &my_background, |
1747 | PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1); | 1747 | PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1); |
1748 | 1748 | ||
1749 | The second call was described above - my_background is in the format of the | 1749 | The second call was described above - my_background is in the format of the |
1750 | final, display, output produced by libpng. Because you now know the format of | 1750 | final, display, output produced by libpng. Because you now know the format of |
1751 | the PNG it is possible to avoid the need to choose either 8-bit or 16-bit | 1751 | the PNG it is possible to avoid the need to choose either 8-bit or 16-bit |
1752 | output and to retain palette images (the palette colors will be modified | 1752 | output and to retain palette images (the palette colors will be modified |
1753 | appropriately and the tRNS chunk removed.) However, if you are doing this, | 1753 | appropriately and the tRNS chunk removed.) However, if you are doing this, |
1754 | take great care not to ask for transformations without checking first that | 1754 | take great care not to ask for transformations without checking first that |
1755 | they apply! | 1755 | they apply! |
1756 | 1756 | ||
1757 | In the first call the background color has the original bit depth and color type | 1757 | In the first call the background color has the original bit depth and color type |
1758 | of the PNG file. So, for palette images the color is supplied as a palette | 1758 | of the PNG file. So, for palette images the color is supplied as a palette |
1759 | index and for low bit greyscale images the color is a reduced bit value in | 1759 | index and for low bit greyscale images the color is a reduced bit value in |
1760 | image_background->gray. | 1760 | image_background->gray. |
1761 | 1761 | ||
1762 | If you didn't call png_set_gamma() before reading the file header, for example | 1762 | If you didn't call png_set_gamma() before reading the file header, for example |
1763 | if you need your code to remain compatible with older versions of libpng prior | 1763 | if you need your code to remain compatible with older versions of libpng prior |
1764 | to libpng-1.5.4, this is the place to call it. | 1764 | to libpng-1.5.4, this is the place to call it. |
1765 | 1765 | ||
1766 | Do not call it if you called png_set_alpha_mode(); doing so will damage the | 1766 | Do not call it if you called png_set_alpha_mode(); doing so will damage the |
1767 | settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is | 1767 | settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is |
1768 | supported then you can certainly do png_set_gamma() before reading the PNG | 1768 | supported then you can certainly do png_set_gamma() before reading the PNG |
1769 | header.) | 1769 | header.) |
1770 | 1770 | ||
1771 | This API unconditionally sets the screen and file gamma values, so it will | 1771 | This API unconditionally sets the screen and file gamma values, so it will |
1772 | override the value in the PNG file unless it is called before the PNG file | 1772 | override the value in the PNG file unless it is called before the PNG file |
1773 | reading starts. For this reason you must always call it with the PNG file | 1773 | reading starts. For this reason you must always call it with the PNG file |
1774 | value when you call it in this position: | 1774 | value when you call it in this position: |
1775 | 1775 | ||
1776 | if (png_get_gAMA(png_ptr, info_ptr, &file_gamma)) | 1776 | if (png_get_gAMA(png_ptr, info_ptr, &file_gamma)) |
1777 | png_set_gamma(png_ptr, screen_gamma, file_gamma); | 1777 | png_set_gamma(png_ptr, screen_gamma, file_gamma); |
1778 | 1778 | ||
1779 | else | 1779 | else |
1780 | png_set_gamma(png_ptr, screen_gamma, 0.45455); | 1780 | png_set_gamma(png_ptr, screen_gamma, 0.45455); |
1781 | 1781 | ||
1782 | If you need to reduce an RGB file to a paletted file, or if a paletted | 1782 | If you need to reduce an RGB file to a paletted file, or if a paletted |
1783 | file has more entries then will fit on your screen, png_set_quantize() | 1783 | file has more entries then will fit on your screen, png_set_quantize() |
1784 | will do that. Note that this is a simple match quantization that merely | 1784 | will do that. Note that this is a simple match quantization that merely |
1785 | finds the closest color available. This should work fairly well with | 1785 | finds the closest color available. This should work fairly well with |
1786 | optimized palettes, but fairly badly with linear color cubes. If you | 1786 | optimized palettes, but fairly badly with linear color cubes. If you |
1787 | pass a palette that is larger than maximum_colors, the file will | 1787 | pass a palette that is larger than maximum_colors, the file will |
1788 | reduce the number of colors in the palette so it will fit into | 1788 | reduce the number of colors in the palette so it will fit into |
1789 | maximum_colors. If there is a histogram, libpng will use it to make | 1789 | maximum_colors. If there is a histogram, libpng will use it to make |
1790 | more intelligent choices when reducing the palette. If there is no | 1790 | more intelligent choices when reducing the palette. If there is no |
1791 | histogram, it may not do as good a job. | 1791 | histogram, it may not do as good a job. |
1792 | 1792 | ||
1793 | if (color_type & PNG_COLOR_MASK_COLOR) | 1793 | if (color_type & PNG_COLOR_MASK_COLOR) |
1794 | { | 1794 | { |
1795 | if (png_get_valid(png_ptr, info_ptr, | 1795 | if (png_get_valid(png_ptr, info_ptr, |
1796 | PNG_INFO_PLTE)) | 1796 | PNG_INFO_PLTE)) |
1797 | { | 1797 | { |
1798 | png_uint_16p histogram = NULL; | 1798 | png_uint_16p histogram = NULL; |
1799 | 1799 | ||
1800 | png_get_hIST(png_ptr, info_ptr, | 1800 | png_get_hIST(png_ptr, info_ptr, |
1801 | &histogram); | 1801 | &histogram); |
1802 | png_set_quantize(png_ptr, palette, num_palette, | 1802 | png_set_quantize(png_ptr, palette, num_palette, |
1803 | max_screen_colors, histogram, 1); | 1803 | max_screen_colors, histogram, 1); |
1804 | } | 1804 | } |
1805 | 1805 | ||
1806 | else | 1806 | else |
1807 | { | 1807 | { |
1808 | png_color std_color_cube[MAX_SCREEN_COLORS] = | 1808 | png_color std_color_cube[MAX_SCREEN_COLORS] = |
1809 | { ... colors ... }; | 1809 | { ... colors ... }; |
1810 | 1810 | ||
1811 | png_set_quantize(png_ptr, std_color_cube, | 1811 | png_set_quantize(png_ptr, std_color_cube, |
1812 | MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, | 1812 | MAX_SCREEN_COLORS, MAX_SCREEN_COLORS, |
1813 | NULL,0); | 1813 | NULL,0); |
1814 | } | 1814 | } |
1815 | } | 1815 | } |
1816 | 1816 | ||
1817 | PNG files describe monochrome as black being zero and white being one. | 1817 | PNG files describe monochrome as black being zero and white being one. |
1818 | The following code will reverse this (make black be one and white be | 1818 | The following code will reverse this (make black be one and white be |
1819 | zero): | 1819 | zero): |
1820 | 1820 | ||
1821 | if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY) | 1821 | if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY) |
1822 | png_set_invert_mono(png_ptr); | 1822 | png_set_invert_mono(png_ptr); |
1823 | 1823 | ||
1824 | This function can also be used to invert grayscale and gray-alpha images: | 1824 | This function can also be used to invert grayscale and gray-alpha images: |
1825 | 1825 | ||
1826 | if (color_type == PNG_COLOR_TYPE_GRAY || | 1826 | if (color_type == PNG_COLOR_TYPE_GRAY || |
1827 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) | 1827 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA) |
1828 | png_set_invert_mono(png_ptr); | 1828 | png_set_invert_mono(png_ptr); |
1829 | 1829 | ||
1830 | PNG files store 16-bit pixels in network byte order (big-endian, | 1830 | PNG files store 16-bit pixels in network byte order (big-endian, |
1831 | ie. most significant bits first). This code changes the storage to the | 1831 | ie. most significant bits first). This code changes the storage to the |
1832 | other way (little-endian, i.e. least significant bits first, the | 1832 | other way (little-endian, i.e. least significant bits first, the |
1833 | way PCs store them): | 1833 | way PCs store them): |
1834 | 1834 | ||
1835 | if (bit_depth == 16) | 1835 | if (bit_depth == 16) |
1836 | png_set_swap(png_ptr); | 1836 | png_set_swap(png_ptr); |
1837 | 1837 | ||
1838 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you | 1838 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you |
1839 | need to change the order the pixels are packed into bytes, you can use: | 1839 | need to change the order the pixels are packed into bytes, you can use: |
1840 | 1840 | ||
1841 | if (bit_depth < 8) | 1841 | if (bit_depth < 8) |
1842 | png_set_packswap(png_ptr); | 1842 | png_set_packswap(png_ptr); |
1843 | 1843 | ||
1844 | Finally, you can write your own transformation function if none of | 1844 | Finally, you can write your own transformation function if none of |
1845 | the existing ones meets your needs. This is done by setting a callback | 1845 | the existing ones meets your needs. This is done by setting a callback |
1846 | with | 1846 | with |
1847 | 1847 | ||
1848 | png_set_read_user_transform_fn(png_ptr, | 1848 | png_set_read_user_transform_fn(png_ptr, |
1849 | read_transform_fn); | 1849 | read_transform_fn); |
1850 | 1850 | ||
1851 | You must supply the function | 1851 | You must supply the function |
1852 | 1852 | ||
1853 | void read_transform_fn(png_structp png_ptr, png_row_infop | 1853 | void read_transform_fn(png_structp png_ptr, png_row_infop |
1854 | row_info, png_bytep data) | 1854 | row_info, png_bytep data) |
1855 | 1855 | ||
1856 | See pngtest.c for a working example. Your function will be called | 1856 | See pngtest.c for a working example. Your function will be called |
1857 | after all of the other transformations have been processed. Take care with | 1857 | after all of the other transformations have been processed. Take care with |
1858 | interlaced images if you do the interlace yourself - the width of the row is the | 1858 | interlaced images if you do the interlace yourself - the width of the row is the |
1859 | width in 'row_info', not the overall image width. | 1859 | width in 'row_info', not the overall image width. |
1860 | 1860 | ||
1861 | If supported, libpng provides two information routines that you can use to find | 1861 | If supported, libpng provides two information routines that you can use to find |
1862 | where you are in processing the image: | 1862 | where you are in processing the image: |
1863 | 1863 | ||
1864 | png_get_current_pass_number(png_structp png_ptr); | 1864 | png_get_current_pass_number(png_structp png_ptr); |
1865 | png_get_current_row_number(png_structp png_ptr); | 1865 | png_get_current_row_number(png_structp png_ptr); |
1866 | 1866 | ||
1867 | Don't try using these outside a transform callback - firstly they are only | 1867 | Don't try using these outside a transform callback - firstly they are only |
1868 | supported if user transforms are supported, secondly they may well return | 1868 | supported if user transforms are supported, secondly they may well return |
1869 | unexpected results unless the row is actually being processed at the moment they | 1869 | unexpected results unless the row is actually being processed at the moment they |
1870 | are called. | 1870 | are called. |
1871 | 1871 | ||
1872 | With interlaced | 1872 | With interlaced |
1873 | images the value returned is the row in the input sub-image image. Use | 1873 | images the value returned is the row in the input sub-image image. Use |
1874 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to | 1874 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to |
1875 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). | 1875 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). |
1876 | 1876 | ||
1877 | The discussion of interlace handling above contains more information on how to | 1877 | The discussion of interlace handling above contains more information on how to |
1878 | use these values. | 1878 | use these values. |
1879 | 1879 | ||
1880 | You can also set up a pointer to a user structure for use by your | 1880 | You can also set up a pointer to a user structure for use by your |
1881 | callback function, and you can inform libpng that your transform | 1881 | callback function, and you can inform libpng that your transform |
1882 | function will change the number of channels or bit depth with the | 1882 | function will change the number of channels or bit depth with the |
1883 | function | 1883 | function |
1884 | 1884 | ||
1885 | png_set_user_transform_info(png_ptr, user_ptr, | 1885 | png_set_user_transform_info(png_ptr, user_ptr, |
1886 | user_depth, user_channels); | 1886 | user_depth, user_channels); |
1887 | 1887 | ||
1888 | The user's application, not libpng, is responsible for allocating and | 1888 | The user's application, not libpng, is responsible for allocating and |
1889 | freeing any memory required for the user structure. | 1889 | freeing any memory required for the user structure. |
1890 | 1890 | ||
1891 | You can retrieve the pointer via the function | 1891 | You can retrieve the pointer via the function |
1892 | png_get_user_transform_ptr(). For example: | 1892 | png_get_user_transform_ptr(). For example: |
1893 | 1893 | ||
1894 | voidp read_user_transform_ptr = | 1894 | voidp read_user_transform_ptr = |
1895 | png_get_user_transform_ptr(png_ptr); | 1895 | png_get_user_transform_ptr(png_ptr); |
1896 | 1896 | ||
1897 | The last thing to handle is interlacing; this is covered in detail below, | 1897 | The last thing to handle is interlacing; this is covered in detail below, |
1898 | but you must call the function here if you want libpng to handle expansion | 1898 | but you must call the function here if you want libpng to handle expansion |
1899 | of the interlaced image. | 1899 | of the interlaced image. |
1900 | 1900 | ||
1901 | number_of_passes = png_set_interlace_handling(png_ptr); | 1901 | number_of_passes = png_set_interlace_handling(png_ptr); |
1902 | 1902 | ||
1903 | After setting the transformations, libpng can update your png_info | 1903 | After setting the transformations, libpng can update your png_info |
1904 | structure to reflect any transformations you've requested with this | 1904 | structure to reflect any transformations you've requested with this |
1905 | call. | 1905 | call. |
1906 | 1906 | ||
1907 | png_read_update_info(png_ptr, info_ptr); | 1907 | png_read_update_info(png_ptr, info_ptr); |
1908 | 1908 | ||
1909 | This is most useful to update the info structure's rowbytes | 1909 | This is most useful to update the info structure's rowbytes |
1910 | field so you can use it to allocate your image memory. This function | 1910 | field so you can use it to allocate your image memory. This function |
1911 | will also update your palette with the correct screen_gamma and | 1911 | will also update your palette with the correct screen_gamma and |
1912 | background if these have been given with the calls above. You may | 1912 | background if these have been given with the calls above. You may |
1913 | only call png_read_update_info() once with a particular info_ptr. | 1913 | only call png_read_update_info() once with a particular info_ptr. |
1914 | 1914 | ||
1915 | After you call png_read_update_info(), you can allocate any | 1915 | After you call png_read_update_info(), you can allocate any |
1916 | memory you need to hold the image. The row data is simply | 1916 | memory you need to hold the image. The row data is simply |
1917 | raw byte data for all forms of images. As the actual allocation | 1917 | raw byte data for all forms of images. As the actual allocation |
1918 | varies among applications, no example will be given. If you | 1918 | varies among applications, no example will be given. If you |
1919 | are allocating one large chunk, you will need to build an | 1919 | are allocating one large chunk, you will need to build an |
1920 | array of pointers to each row, as it will be needed for some | 1920 | array of pointers to each row, as it will be needed for some |
1921 | of the functions below. | 1921 | of the functions below. |
1922 | 1922 | ||
1923 | Remember: Before you call png_read_update_info(), the png_get_*() | 1923 | Remember: Before you call png_read_update_info(), the png_get_*() |
1924 | functions return the values corresponding to the original PNG image. | 1924 | functions return the values corresponding to the original PNG image. |
1925 | After you call png_read_update_info the values refer to the image | 1925 | After you call png_read_update_info the values refer to the image |
1926 | that libpng will output. Consequently you must call all the png_set_ | 1926 | that libpng will output. Consequently you must call all the png_set_ |
1927 | functions before you call png_read_update_info(). This is particularly | 1927 | functions before you call png_read_update_info(). This is particularly |
1928 | important for png_set_interlace_handling() - if you are going to call | 1928 | important for png_set_interlace_handling() - if you are going to call |
1929 | png_read_update_info() you must call png_set_interlace_handling() before | 1929 | png_read_update_info() you must call png_set_interlace_handling() before |
1930 | it unless you want to receive interlaced output. | 1930 | it unless you want to receive interlaced output. |
1931 | 1931 | ||
1932 | Reading image data | 1932 | Reading image data |
1933 | 1933 | ||
1934 | After you've allocated memory, you can read the image data. | 1934 | After you've allocated memory, you can read the image data. |
1935 | The simplest way to do this is in one function call. If you are | 1935 | The simplest way to do this is in one function call. If you are |
1936 | allocating enough memory to hold the whole image, you can just | 1936 | allocating enough memory to hold the whole image, you can just |
1937 | call png_read_image() and libpng will read in all the image data | 1937 | call png_read_image() and libpng will read in all the image data |
1938 | and put it in the memory area supplied. You will need to pass in | 1938 | and put it in the memory area supplied. You will need to pass in |
1939 | an array of pointers to each row. | 1939 | an array of pointers to each row. |
1940 | 1940 | ||
1941 | This function automatically handles interlacing, so you don't | 1941 | This function automatically handles interlacing, so you don't |
1942 | need to call png_set_interlace_handling() (unless you call | 1942 | need to call png_set_interlace_handling() (unless you call |
1943 | png_read_update_info()) or call this function multiple times, or any | 1943 | png_read_update_info()) or call this function multiple times, or any |
1944 | of that other stuff necessary with png_read_rows(). | 1944 | of that other stuff necessary with png_read_rows(). |
1945 | 1945 | ||
1946 | png_read_image(png_ptr, row_pointers); | 1946 | png_read_image(png_ptr, row_pointers); |
1947 | 1947 | ||
1948 | where row_pointers is: | 1948 | where row_pointers is: |
1949 | 1949 | ||
1950 | png_bytep row_pointers[height]; | 1950 | png_bytep row_pointers[height]; |
1951 | 1951 | ||
1952 | You can point to void or char or whatever you use for pixels. | 1952 | You can point to void or char or whatever you use for pixels. |
1953 | 1953 | ||
1954 | If you don't want to read in the whole image at once, you can | 1954 | If you don't want to read in the whole image at once, you can |
1955 | use png_read_rows() instead. If there is no interlacing (check | 1955 | use png_read_rows() instead. If there is no interlacing (check |
1956 | interlace_type == PNG_INTERLACE_NONE), this is simple: | 1956 | interlace_type == PNG_INTERLACE_NONE), this is simple: |
1957 | 1957 | ||
1958 | png_read_rows(png_ptr, row_pointers, NULL, | 1958 | png_read_rows(png_ptr, row_pointers, NULL, |
1959 | number_of_rows); | 1959 | number_of_rows); |
1960 | 1960 | ||
1961 | where row_pointers is the same as in the png_read_image() call. | 1961 | where row_pointers is the same as in the png_read_image() call. |
1962 | 1962 | ||
1963 | If you are doing this just one row at a time, you can do this with | 1963 | If you are doing this just one row at a time, you can do this with |
1964 | a single row_pointer instead of an array of row_pointers: | 1964 | a single row_pointer instead of an array of row_pointers: |
1965 | 1965 | ||
1966 | png_bytep row_pointer = row; | 1966 | png_bytep row_pointer = row; |
1967 | png_read_row(png_ptr, row_pointer, NULL); | 1967 | png_read_row(png_ptr, row_pointer, NULL); |
1968 | 1968 | ||
1969 | If the file is interlaced (interlace_type != 0 in the IHDR chunk), things | 1969 | If the file is interlaced (interlace_type != 0 in the IHDR chunk), things |
1970 | get somewhat harder. The only current (PNG Specification version 1.2) | 1970 | get somewhat harder. The only current (PNG Specification version 1.2) |
1971 | interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7); | 1971 | interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7); |
1972 | a somewhat complicated 2D interlace scheme, known as Adam7, that | 1972 | a somewhat complicated 2D interlace scheme, known as Adam7, that |
1973 | breaks down an image into seven smaller images of varying size, based | 1973 | breaks down an image into seven smaller images of varying size, based |
1974 | on an 8x8 grid. This number is defined (from libpng 1.5) as | 1974 | on an 8x8 grid. This number is defined (from libpng 1.5) as |
1975 | PNG_INTERLACE_ADAM7_PASSES in png.h | 1975 | PNG_INTERLACE_ADAM7_PASSES in png.h |
1976 | 1976 | ||
1977 | libpng can fill out those images or it can give them to you "as is". | 1977 | libpng can fill out those images or it can give them to you "as is". |
1978 | It is almost always better to have libpng handle the interlacing for you. | 1978 | It is almost always better to have libpng handle the interlacing for you. |
1979 | If you want the images filled out, there are two ways to do that. The one | 1979 | If you want the images filled out, there are two ways to do that. The one |
1980 | mentioned in the PNG specification is to expand each pixel to cover | 1980 | mentioned in the PNG specification is to expand each pixel to cover |
1981 | those pixels that have not been read yet (the "rectangle" method). | 1981 | those pixels that have not been read yet (the "rectangle" method). |
1982 | This results in a blocky image for the first pass, which gradually | 1982 | This results in a blocky image for the first pass, which gradually |
1983 | smooths out as more pixels are read. The other method is the "sparkle" | 1983 | smooths out as more pixels are read. The other method is the "sparkle" |
1984 | method, where pixels are drawn only in their final locations, with the | 1984 | method, where pixels are drawn only in their final locations, with the |
1985 | rest of the image remaining whatever colors they were initialized to | 1985 | rest of the image remaining whatever colors they were initialized to |
1986 | before the start of the read. The first method usually looks better, | 1986 | before the start of the read. The first method usually looks better, |
1987 | but tends to be slower, as there are more pixels to put in the rows. | 1987 | but tends to be slower, as there are more pixels to put in the rows. |
1988 | 1988 | ||
1989 | If, as is likely, you want libpng to expand the images, call this before | 1989 | If, as is likely, you want libpng to expand the images, call this before |
1990 | calling png_start_read_image() or png_read_update_info(): | 1990 | calling png_start_read_image() or png_read_update_info(): |
1991 | 1991 | ||
1992 | if (interlace_type == PNG_INTERLACE_ADAM7) | 1992 | if (interlace_type == PNG_INTERLACE_ADAM7) |
1993 | number_of_passes | 1993 | number_of_passes |
1994 | = png_set_interlace_handling(png_ptr); | 1994 | = png_set_interlace_handling(png_ptr); |
1995 | 1995 | ||
1996 | This will return the number of passes needed. Currently, this is seven, | 1996 | This will return the number of passes needed. Currently, this is seven, |
1997 | but may change if another interlace type is added. This function can be | 1997 | but may change if another interlace type is added. This function can be |
1998 | called even if the file is not interlaced, where it will return one pass. | 1998 | called even if the file is not interlaced, where it will return one pass. |
1999 | You then need to read the whole image 'number_of_passes' times. Each time | 1999 | You then need to read the whole image 'number_of_passes' times. Each time |
2000 | will distribute the pixels from the current pass to the correct place in | 2000 | will distribute the pixels from the current pass to the correct place in |
2001 | the output image, so you need to supply the same rows to png_read_rows in | 2001 | the output image, so you need to supply the same rows to png_read_rows in |
2002 | each pass. | 2002 | each pass. |
2003 | 2003 | ||
2004 | If you are not going to display the image after each pass, but are | 2004 | If you are not going to display the image after each pass, but are |
2005 | going to wait until the entire image is read in, use the sparkle | 2005 | going to wait until the entire image is read in, use the sparkle |
2006 | effect. This effect is faster and the end result of either method | 2006 | effect. This effect is faster and the end result of either method |
2007 | is exactly the same. If you are planning on displaying the image | 2007 | is exactly the same. If you are planning on displaying the image |
2008 | after each pass, the "rectangle" effect is generally considered the | 2008 | after each pass, the "rectangle" effect is generally considered the |
2009 | better looking one. | 2009 | better looking one. |
2010 | 2010 | ||
2011 | If you only want the "sparkle" effect, just call png_read_rows() as | 2011 | If you only want the "sparkle" effect, just call png_read_rows() as |
2012 | normal, with the third parameter NULL. Make sure you make pass over | 2012 | normal, with the third parameter NULL. Make sure you make pass over |
2013 | the image number_of_passes times, and you don't change the data in the | 2013 | the image number_of_passes times, and you don't change the data in the |
2014 | rows between calls. You can change the locations of the data, just | 2014 | rows between calls. You can change the locations of the data, just |
2015 | not the data. Each pass only writes the pixels appropriate for that | 2015 | not the data. Each pass only writes the pixels appropriate for that |
2016 | pass, and assumes the data from previous passes is still valid. | 2016 | pass, and assumes the data from previous passes is still valid. |
2017 | 2017 | ||
2018 | png_read_rows(png_ptr, row_pointers, NULL, | 2018 | png_read_rows(png_ptr, row_pointers, NULL, |
2019 | number_of_rows); | 2019 | number_of_rows); |
2020 | 2020 | ||
2021 | If you only want the first effect (the rectangles), do the same as | 2021 | If you only want the first effect (the rectangles), do the same as |
2022 | before except pass the row buffer in the third parameter, and leave | 2022 | before except pass the row buffer in the third parameter, and leave |
2023 | the second parameter NULL. | 2023 | the second parameter NULL. |
2024 | 2024 | ||
2025 | png_read_rows(png_ptr, NULL, row_pointers, | 2025 | png_read_rows(png_ptr, NULL, row_pointers, |
2026 | number_of_rows); | 2026 | number_of_rows); |
2027 | 2027 | ||
2028 | If you don't want libpng to handle the interlacing details, just call | 2028 | If you don't want libpng to handle the interlacing details, just call |
2029 | png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images. | 2029 | png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images. |
2030 | Each of the images is a valid image by itself, however you will almost | 2030 | Each of the images is a valid image by itself, however you will almost |
2031 | certainly need to distribute the pixels from each sub-image to the | 2031 | certainly need to distribute the pixels from each sub-image to the |
2032 | correct place. This is where everything gets very tricky. | 2032 | correct place. This is where everything gets very tricky. |
2033 | 2033 | ||
2034 | If you want to retrieve the separate images you must pass the correct | 2034 | If you want to retrieve the separate images you must pass the correct |
2035 | number of rows to each successive call of png_read_rows(). The calculation | 2035 | number of rows to each successive call of png_read_rows(). The calculation |
2036 | gets pretty complicated for small images, where some sub-images may | 2036 | gets pretty complicated for small images, where some sub-images may |
2037 | not even exist because either their width or height ends up zero. | 2037 | not even exist because either their width or height ends up zero. |
2038 | libpng provides two macros to help you in 1.5 and later versions: | 2038 | libpng provides two macros to help you in 1.5 and later versions: |
2039 | 2039 | ||
2040 | png_uint_32 width = PNG_PASS_COLS(image_width, pass_number); | 2040 | png_uint_32 width = PNG_PASS_COLS(image_width, pass_number); |
2041 | png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number); | 2041 | png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number); |
2042 | 2042 | ||
2043 | Respectively these tell you the width and height of the sub-image | 2043 | Respectively these tell you the width and height of the sub-image |
2044 | corresponding to the numbered pass. 'pass' is in in the range 0 to 6 - | 2044 | corresponding to the numbered pass. 'pass' is in in the range 0 to 6 - |
2045 | this can be confusing because the specification refers to the same passes | 2045 | this can be confusing because the specification refers to the same passes |
2046 | as 1 to 7! Be careful, you must check both the width and height before | 2046 | as 1 to 7! Be careful, you must check both the width and height before |
2047 | calling png_read_rows() and not call it for that pass if either is zero. | 2047 | calling png_read_rows() and not call it for that pass if either is zero. |
2048 | 2048 | ||
2049 | You can, of course, read each sub-image row by row. If you want to | 2049 | You can, of course, read each sub-image row by row. If you want to |
2050 | produce optimal code to make a pixel-by-pixel transformation of an | 2050 | produce optimal code to make a pixel-by-pixel transformation of an |
2051 | interlaced image this is the best approach; read each row of each pass, | 2051 | interlaced image this is the best approach; read each row of each pass, |
2052 | transform it, and write it out to a new interlaced image. | 2052 | transform it, and write it out to a new interlaced image. |
2053 | 2053 | ||
2054 | If you want to de-interlace the image yourself libpng provides further | 2054 | If you want to de-interlace the image yourself libpng provides further |
2055 | macros to help that tell you where to place the pixels in the output image. | 2055 | macros to help that tell you where to place the pixels in the output image. |
2056 | Because the interlacing scheme is rectangular - sub-image pixels are always | 2056 | Because the interlacing scheme is rectangular - sub-image pixels are always |
2057 | arranged on a rectangular grid - all you need to know for each pass is the | 2057 | arranged on a rectangular grid - all you need to know for each pass is the |
2058 | starting column and row in the output image of the first pixel plus the | 2058 | starting column and row in the output image of the first pixel plus the |
2059 | spacing between each pixel. As of libpng 1.5 there are four macros to | 2059 | spacing between each pixel. As of libpng 1.5 there are four macros to |
2060 | retrieve this information: | 2060 | retrieve this information: |
2061 | 2061 | ||
2062 | png_uint_32 x = PNG_PASS_START_COL(pass); | 2062 | png_uint_32 x = PNG_PASS_START_COL(pass); |
2063 | png_uint_32 y = PNG_PASS_START_ROW(pass); | 2063 | png_uint_32 y = PNG_PASS_START_ROW(pass); |
2064 | png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass); | 2064 | png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass); |
2065 | png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass); | 2065 | png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass); |
2066 | 2066 | ||
2067 | These allow you to write the obvious loop: | 2067 | These allow you to write the obvious loop: |
2068 | 2068 | ||
2069 | png_uint_32 input_y = 0; | 2069 | png_uint_32 input_y = 0; |
2070 | png_uint_32 output_y = PNG_PASS_START_ROW(pass); | 2070 | png_uint_32 output_y = PNG_PASS_START_ROW(pass); |
2071 | 2071 | ||
2072 | while (output_y < output_image_height) | 2072 | while (output_y < output_image_height) |
2073 | { | 2073 | { |
2074 | png_uint_32 input_x = 0; | 2074 | png_uint_32 input_x = 0; |
2075 | png_uint_32 output_x = PNG_PASS_START_COL(pass); | 2075 | png_uint_32 output_x = PNG_PASS_START_COL(pass); |
2076 | 2076 | ||
2077 | while (output_x < output_image_width) | 2077 | while (output_x < output_image_width) |
2078 | { | 2078 | { |
2079 | image[output_y][output_x] = | 2079 | image[output_y][output_x] = |
2080 | subimage[pass][input_y][input_x++]; | 2080 | subimage[pass][input_y][input_x++]; |
2081 | 2081 | ||
2082 | output_x += xStep; | 2082 | output_x += xStep; |
2083 | } | 2083 | } |
2084 | 2084 | ||
2085 | ++input_y; | 2085 | ++input_y; |
2086 | output_y += yStep; | 2086 | output_y += yStep; |
2087 | } | 2087 | } |
2088 | 2088 | ||
2089 | Notice that the steps between successive output rows and columns are | 2089 | Notice that the steps between successive output rows and columns are |
2090 | returned as shifts. This is possible because the pixels in the subimages | 2090 | returned as shifts. This is possible because the pixels in the subimages |
2091 | are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original | 2091 | are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original |
2092 | image. In practice you may need to directly calculate the output coordinate | 2092 | image. In practice you may need to directly calculate the output coordinate |
2093 | given an input coordinate. libpng provides two further macros for this | 2093 | given an input coordinate. libpng provides two further macros for this |
2094 | purpose: | 2094 | purpose: |
2095 | 2095 | ||
2096 | png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass); | 2096 | png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass); |
2097 | png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass); | 2097 | png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass); |
2098 | 2098 | ||
2099 | Finally a pair of macros are provided to tell you if a particular image | 2099 | Finally a pair of macros are provided to tell you if a particular image |
2100 | row or column appears in a given pass: | 2100 | row or column appears in a given pass: |
2101 | 2101 | ||
2102 | int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass); | 2102 | int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass); |
2103 | int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass); | 2103 | int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass); |
2104 | 2104 | ||
2105 | Bear in mind that you will probably also need to check the width and height | 2105 | Bear in mind that you will probably also need to check the width and height |
2106 | of the pass in addition to the above to be sure the pass even exists! | 2106 | of the pass in addition to the above to be sure the pass even exists! |
2107 | 2107 | ||
2108 | With any luck you are convinced by now that you don't want to do your own | 2108 | With any luck you are convinced by now that you don't want to do your own |
2109 | interlace handling. In reality normally the only good reason for doing this | 2109 | interlace handling. In reality normally the only good reason for doing this |
2110 | is if you are processing PNG files on a pixel-by-pixel basis and don't want | 2110 | is if you are processing PNG files on a pixel-by-pixel basis and don't want |
2111 | to load the whole file into memory when it is interlaced. | 2111 | to load the whole file into memory when it is interlaced. |
2112 | 2112 | ||
2113 | libpng includes a test program, pngvalid, that illustrates reading and | 2113 | libpng includes a test program, pngvalid, that illustrates reading and |
2114 | writing of interlaced images. If you can't get interlacing to work in your | 2114 | writing of interlaced images. If you can't get interlacing to work in your |
2115 | code and don't want to leave it to libpng (the recommended approach), see | 2115 | code and don't want to leave it to libpng (the recommended approach), see |
2116 | how pngvalid.c does it. | 2116 | how pngvalid.c does it. |
2117 | 2117 | ||
2118 | Finishing a sequential read | 2118 | Finishing a sequential read |
2119 | 2119 | ||
2120 | After you are finished reading the image through the | 2120 | After you are finished reading the image through the |
2121 | low-level interface, you can finish reading the file. If you are | 2121 | low-level interface, you can finish reading the file. If you are |
2122 | interested in comments or time, which may be stored either before or | 2122 | interested in comments or time, which may be stored either before or |
2123 | after the image data, you should pass the separate png_info struct if | 2123 | after the image data, you should pass the separate png_info struct if |
2124 | you want to keep the comments from before and after the image | 2124 | you want to keep the comments from before and after the image |
2125 | separate. | 2125 | separate. |
2126 | 2126 | ||
2127 | png_infop end_info = png_create_info_struct(png_ptr); | 2127 | png_infop end_info = png_create_info_struct(png_ptr); |
2128 | 2128 | ||
2129 | if (!end_info) | 2129 | if (!end_info) |
2130 | { | 2130 | { |
2131 | png_destroy_read_struct(&png_ptr, &info_ptr, | 2131 | png_destroy_read_struct(&png_ptr, &info_ptr, |
2132 | (png_infopp)NULL); | 2132 | (png_infopp)NULL); |
2133 | return (ERROR); | 2133 | return (ERROR); |
2134 | } | 2134 | } |
2135 | 2135 | ||
2136 | png_read_end(png_ptr, end_info); | 2136 | png_read_end(png_ptr, end_info); |
2137 | 2137 | ||
2138 | If you are not interested, you should still call png_read_end() | 2138 | If you are not interested, you should still call png_read_end() |
2139 | but you can pass NULL, avoiding the need to create an end_info structure. | 2139 | but you can pass NULL, avoiding the need to create an end_info structure. |
2140 | 2140 | ||
2141 | png_read_end(png_ptr, (png_infop)NULL); | 2141 | png_read_end(png_ptr, (png_infop)NULL); |
2142 | 2142 | ||
2143 | If you don't call png_read_end(), then your file pointer will be | 2143 | If you don't call png_read_end(), then your file pointer will be |
2144 | left pointing to the first chunk after the last IDAT, which is probably | 2144 | left pointing to the first chunk after the last IDAT, which is probably |
2145 | not what you want if you expect to read something beyond the end of | 2145 | not what you want if you expect to read something beyond the end of |
2146 | the PNG datastream. | 2146 | the PNG datastream. |
2147 | 2147 | ||
2148 | When you are done, you can free all memory allocated by libpng like this: | 2148 | When you are done, you can free all memory allocated by libpng like this: |
2149 | 2149 | ||
2150 | png_destroy_read_struct(&png_ptr, &info_ptr, | 2150 | png_destroy_read_struct(&png_ptr, &info_ptr, |
2151 | &end_info); | 2151 | &end_info); |
2152 | 2152 | ||
2153 | or, if you didn't create an end_info structure, | 2153 | or, if you didn't create an end_info structure, |
2154 | 2154 | ||
2155 | png_destroy_read_struct(&png_ptr, &info_ptr, | 2155 | png_destroy_read_struct(&png_ptr, &info_ptr, |
2156 | (png_infopp)NULL); | 2156 | (png_infopp)NULL); |
2157 | 2157 | ||
2158 | It is also possible to individually free the info_ptr members that | 2158 | It is also possible to individually free the info_ptr members that |
2159 | point to libpng-allocated storage with the following function: | 2159 | point to libpng-allocated storage with the following function: |
2160 | 2160 | ||
2161 | png_free_data(png_ptr, info_ptr, mask, seq) | 2161 | png_free_data(png_ptr, info_ptr, mask, seq) |
2162 | 2162 | ||
2163 | mask - identifies data to be freed, a mask | 2163 | mask - identifies data to be freed, a mask |
2164 | containing the bitwise OR of one or | 2164 | containing the bitwise OR of one or |
2165 | more of | 2165 | more of |
2166 | PNG_FREE_PLTE, PNG_FREE_TRNS, | 2166 | PNG_FREE_PLTE, PNG_FREE_TRNS, |
2167 | PNG_FREE_HIST, PNG_FREE_ICCP, | 2167 | PNG_FREE_HIST, PNG_FREE_ICCP, |
2168 | PNG_FREE_PCAL, PNG_FREE_ROWS, | 2168 | PNG_FREE_PCAL, PNG_FREE_ROWS, |
2169 | PNG_FREE_SCAL, PNG_FREE_SPLT, | 2169 | PNG_FREE_SCAL, PNG_FREE_SPLT, |
2170 | PNG_FREE_TEXT, PNG_FREE_UNKN, | 2170 | PNG_FREE_TEXT, PNG_FREE_UNKN, |
2171 | or simply PNG_FREE_ALL | 2171 | or simply PNG_FREE_ALL |
2172 | 2172 | ||
2173 | seq - sequence number of item to be freed | 2173 | seq - sequence number of item to be freed |
2174 | (-1 for all items) | 2174 | (-1 for all items) |
2175 | 2175 | ||
2176 | This function may be safely called when the relevant storage has | 2176 | This function may be safely called when the relevant storage has |
2177 | already been freed, or has not yet been allocated, or was allocated | 2177 | already been freed, or has not yet been allocated, or was allocated |
2178 | by the user and not by libpng, and will in those cases do nothing. | 2178 | by the user and not by libpng, and will in those cases do nothing. |
2179 | The "seq" parameter is ignored if only one item of the selected data | 2179 | The "seq" parameter is ignored if only one item of the selected data |
2180 | type, such as PLTE, is allowed. If "seq" is not -1, and multiple items | 2180 | type, such as PLTE, is allowed. If "seq" is not -1, and multiple items |
2181 | are allowed for the data type identified in the mask, such as text or | 2181 | are allowed for the data type identified in the mask, such as text or |
2182 | sPLT, only the n'th item in the structure is freed, where n is "seq". | 2182 | sPLT, only the n'th item in the structure is freed, where n is "seq". |
2183 | 2183 | ||
2184 | The default behavior is only to free data that was allocated internally | 2184 | The default behavior is only to free data that was allocated internally |
2185 | by libpng. This can be changed, so that libpng will not free the data, | 2185 | by libpng. This can be changed, so that libpng will not free the data, |
2186 | or so that it will free data that was allocated by the user with png_malloc() | 2186 | or so that it will free data that was allocated by the user with png_malloc() |
2187 | or png_zalloc() and passed in via a png_set_*() function, with | 2187 | or png_zalloc() and passed in via a png_set_*() function, with |
2188 | 2188 | ||
2189 | png_data_freer(png_ptr, info_ptr, freer, mask) | 2189 | png_data_freer(png_ptr, info_ptr, freer, mask) |
2190 | 2190 | ||
2191 | freer - one of | 2191 | freer - one of |
2192 | PNG_DESTROY_WILL_FREE_DATA | 2192 | PNG_DESTROY_WILL_FREE_DATA |
2193 | PNG_SET_WILL_FREE_DATA | 2193 | PNG_SET_WILL_FREE_DATA |
2194 | PNG_USER_WILL_FREE_DATA | 2194 | PNG_USER_WILL_FREE_DATA |
2195 | 2195 | ||
2196 | mask - which data elements are affected | 2196 | mask - which data elements are affected |
2197 | same choices as in png_free_data() | 2197 | same choices as in png_free_data() |
2198 | 2198 | ||
2199 | This function only affects data that has already been allocated. | 2199 | This function only affects data that has already been allocated. |
2200 | You can call this function after reading the PNG data but before calling | 2200 | You can call this function after reading the PNG data but before calling |
2201 | any png_set_*() functions, to control whether the user or the png_set_*() | 2201 | any png_set_*() functions, to control whether the user or the png_set_*() |
2202 | function is responsible for freeing any existing data that might be present, | 2202 | function is responsible for freeing any existing data that might be present, |
2203 | and again after the png_set_*() functions to control whether the user | 2203 | and again after the png_set_*() functions to control whether the user |
2204 | or png_destroy_*() is supposed to free the data. When the user assumes | 2204 | or png_destroy_*() is supposed to free the data. When the user assumes |
2205 | responsibility for libpng-allocated data, the application must use | 2205 | responsibility for libpng-allocated data, the application must use |
2206 | png_free() to free it, and when the user transfers responsibility to libpng | 2206 | png_free() to free it, and when the user transfers responsibility to libpng |
2207 | for data that the user has allocated, the user must have used png_malloc() | 2207 | for data that the user has allocated, the user must have used png_malloc() |
2208 | or png_zalloc() to allocate it. | 2208 | or png_zalloc() to allocate it. |
2209 | 2209 | ||
2210 | If you allocated your row_pointers in a single block, as suggested above in | 2210 | If you allocated your row_pointers in a single block, as suggested above in |
2211 | the description of the high level read interface, you must not transfer | 2211 | the description of the high level read interface, you must not transfer |
2212 | responsibility for freeing it to the png_set_rows or png_read_destroy function, | 2212 | responsibility for freeing it to the png_set_rows or png_read_destroy function, |
2213 | because they would also try to free the individual row_pointers[i]. | 2213 | because they would also try to free the individual row_pointers[i]. |
2214 | 2214 | ||
2215 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword | 2215 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword |
2216 | separately, do not transfer responsibility for freeing text_ptr to libpng, | 2216 | separately, do not transfer responsibility for freeing text_ptr to libpng, |
2217 | because when libpng fills a png_text structure it combines these members with | 2217 | because when libpng fills a png_text structure it combines these members with |
2218 | the key member, and png_free_data() will free only text_ptr.key. Similarly, | 2218 | the key member, and png_free_data() will free only text_ptr.key. Similarly, |
2219 | if you transfer responsibility for free'ing text_ptr from libpng to your | 2219 | if you transfer responsibility for free'ing text_ptr from libpng to your |
2220 | application, your application must not separately free those members. | 2220 | application, your application must not separately free those members. |
2221 | 2221 | ||
2222 | The png_free_data() function will turn off the "valid" flag for anything | 2222 | The png_free_data() function will turn off the "valid" flag for anything |
2223 | it frees. If you need to turn the flag off for a chunk that was freed by | 2223 | it frees. If you need to turn the flag off for a chunk that was freed by |
2224 | your application instead of by libpng, you can use | 2224 | your application instead of by libpng, you can use |
2225 | 2225 | ||
2226 | png_set_invalid(png_ptr, info_ptr, mask); | 2226 | png_set_invalid(png_ptr, info_ptr, mask); |
2227 | 2227 | ||
2228 | mask - identifies the chunks to be made invalid, | 2228 | mask - identifies the chunks to be made invalid, |
2229 | containing the bitwise OR of one or | 2229 | containing the bitwise OR of one or |
2230 | more of | 2230 | more of |
2231 | PNG_INFO_gAMA, PNG_INFO_sBIT, | 2231 | PNG_INFO_gAMA, PNG_INFO_sBIT, |
2232 | PNG_INFO_cHRM, PNG_INFO_PLTE, | 2232 | PNG_INFO_cHRM, PNG_INFO_PLTE, |
2233 | PNG_INFO_tRNS, PNG_INFO_bKGD, | 2233 | PNG_INFO_tRNS, PNG_INFO_bKGD, |
2234 | PNG_INFO_hIST, PNG_INFO_pHYs, | 2234 | PNG_INFO_hIST, PNG_INFO_pHYs, |
2235 | PNG_INFO_oFFs, PNG_INFO_tIME, | 2235 | PNG_INFO_oFFs, PNG_INFO_tIME, |
2236 | PNG_INFO_pCAL, PNG_INFO_sRGB, | 2236 | PNG_INFO_pCAL, PNG_INFO_sRGB, |
2237 | PNG_INFO_iCCP, PNG_INFO_sPLT, | 2237 | PNG_INFO_iCCP, PNG_INFO_sPLT, |
2238 | PNG_INFO_sCAL, PNG_INFO_IDAT | 2238 | PNG_INFO_sCAL, PNG_INFO_IDAT |
2239 | 2239 | ||
2240 | For a more compact example of reading a PNG image, see the file example.c. | 2240 | For a more compact example of reading a PNG image, see the file example.c. |
2241 | 2241 | ||
2242 | Reading PNG files progressively | 2242 | Reading PNG files progressively |
2243 | 2243 | ||
2244 | The progressive reader is slightly different then the non-progressive | 2244 | The progressive reader is slightly different then the non-progressive |
2245 | reader. Instead of calling png_read_info(), png_read_rows(), and | 2245 | reader. Instead of calling png_read_info(), png_read_rows(), and |
2246 | png_read_end(), you make one call to png_process_data(), which calls | 2246 | png_read_end(), you make one call to png_process_data(), which calls |
2247 | callbacks when it has the info, a row, or the end of the image. You | 2247 | callbacks when it has the info, a row, or the end of the image. You |
2248 | set up these callbacks with png_set_progressive_read_fn(). You don't | 2248 | set up these callbacks with png_set_progressive_read_fn(). You don't |
2249 | have to worry about the input/output functions of libpng, as you are | 2249 | have to worry about the input/output functions of libpng, as you are |
2250 | giving the library the data directly in png_process_data(). I will | 2250 | giving the library the data directly in png_process_data(). I will |
2251 | assume that you have read the section on reading PNG files above, | 2251 | assume that you have read the section on reading PNG files above, |
2252 | so I will only highlight the differences (although I will show | 2252 | so I will only highlight the differences (although I will show |
2253 | all of the code). | 2253 | all of the code). |
2254 | 2254 | ||
2255 | png_structp png_ptr; | 2255 | png_structp png_ptr; |
2256 | png_infop info_ptr; | 2256 | png_infop info_ptr; |
2257 | 2257 | ||
2258 | /* An example code fragment of how you would | 2258 | /* An example code fragment of how you would |
2259 | initialize the progressive reader in your | 2259 | initialize the progressive reader in your |
2260 | application. */ | 2260 | application. */ |
2261 | int | 2261 | int |
2262 | initialize_png_reader() | 2262 | initialize_png_reader() |
2263 | { | 2263 | { |
2264 | png_ptr = png_create_read_struct | 2264 | png_ptr = png_create_read_struct |
2265 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | 2265 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, |
2266 | user_error_fn, user_warning_fn); | 2266 | user_error_fn, user_warning_fn); |
2267 | 2267 | ||
2268 | if (!png_ptr) | 2268 | if (!png_ptr) |
2269 | return (ERROR); | 2269 | return (ERROR); |
2270 | 2270 | ||
2271 | info_ptr = png_create_info_struct(png_ptr); | 2271 | info_ptr = png_create_info_struct(png_ptr); |
2272 | 2272 | ||
2273 | if (!info_ptr) | 2273 | if (!info_ptr) |
2274 | { | 2274 | { |
2275 | png_destroy_read_struct(&png_ptr, | 2275 | png_destroy_read_struct(&png_ptr, |
2276 | (png_infopp)NULL, (png_infopp)NULL); | 2276 | (png_infopp)NULL, (png_infopp)NULL); |
2277 | return (ERROR); | 2277 | return (ERROR); |
2278 | } | 2278 | } |
2279 | 2279 | ||
2280 | if (setjmp(png_jmpbuf(png_ptr))) | 2280 | if (setjmp(png_jmpbuf(png_ptr))) |
2281 | { | 2281 | { |
2282 | png_destroy_read_struct(&png_ptr, &info_ptr, | 2282 | png_destroy_read_struct(&png_ptr, &info_ptr, |
2283 | (png_infopp)NULL); | 2283 | (png_infopp)NULL); |
2284 | return (ERROR); | 2284 | return (ERROR); |
2285 | } | 2285 | } |
2286 | 2286 | ||
2287 | /* This one's new. You can provide functions | 2287 | /* This one's new. You can provide functions |
2288 | to be called when the header info is valid, | 2288 | to be called when the header info is valid, |
2289 | when each row is completed, and when the image | 2289 | when each row is completed, and when the image |
2290 | is finished. If you aren't using all functions, | 2290 | is finished. If you aren't using all functions, |
2291 | you can specify NULL parameters. Even when all | 2291 | you can specify NULL parameters. Even when all |
2292 | three functions are NULL, you need to call | 2292 | three functions are NULL, you need to call |
2293 | png_set_progressive_read_fn(). You can use | 2293 | png_set_progressive_read_fn(). You can use |
2294 | any struct as the user_ptr (cast to a void pointer | 2294 | any struct as the user_ptr (cast to a void pointer |
2295 | for the function call), and retrieve the pointer | 2295 | for the function call), and retrieve the pointer |
2296 | from inside the callbacks using the function | 2296 | from inside the callbacks using the function |
2297 | 2297 | ||
2298 | png_get_progressive_ptr(png_ptr); | 2298 | png_get_progressive_ptr(png_ptr); |
2299 | 2299 | ||
2300 | which will return a void pointer, which you have | 2300 | which will return a void pointer, which you have |
2301 | to cast appropriately. | 2301 | to cast appropriately. |
2302 | */ | 2302 | */ |
2303 | png_set_progressive_read_fn(png_ptr, (void *)user_ptr, | 2303 | png_set_progressive_read_fn(png_ptr, (void *)user_ptr, |
2304 | info_callback, row_callback, end_callback); | 2304 | info_callback, row_callback, end_callback); |
2305 | 2305 | ||
2306 | return 0; | 2306 | return 0; |
2307 | } | 2307 | } |
2308 | 2308 | ||
2309 | /* A code fragment that you call as you receive blocks | 2309 | /* A code fragment that you call as you receive blocks |
2310 | of data */ | 2310 | of data */ |
2311 | int | 2311 | int |
2312 | process_data(png_bytep buffer, png_uint_32 length) | 2312 | process_data(png_bytep buffer, png_uint_32 length) |
2313 | { | 2313 | { |
2314 | if (setjmp(png_jmpbuf(png_ptr))) | 2314 | if (setjmp(png_jmpbuf(png_ptr))) |
2315 | { | 2315 | { |
2316 | png_destroy_read_struct(&png_ptr, &info_ptr, | 2316 | png_destroy_read_struct(&png_ptr, &info_ptr, |
2317 | (png_infopp)NULL); | 2317 | (png_infopp)NULL); |
2318 | return (ERROR); | 2318 | return (ERROR); |
2319 | } | 2319 | } |
2320 | 2320 | ||
2321 | /* This one's new also. Simply give it a chunk | 2321 | /* This one's new also. Simply give it a chunk |
2322 | of data from the file stream (in order, of | 2322 | of data from the file stream (in order, of |
2323 | course). On machines with segmented memory | 2323 | course). On machines with segmented memory |
2324 | models machines, don't give it any more than | 2324 | models machines, don't give it any more than |
2325 | 64K. The library seems to run fine with sizes | 2325 | 64K. The library seems to run fine with sizes |
2326 | of 4K. Although you can give it much less if | 2326 | of 4K. Although you can give it much less if |
2327 | necessary (I assume you can give it chunks of | 2327 | necessary (I assume you can give it chunks of |
2328 | 1 byte, I haven't tried less then 256 bytes | 2328 | 1 byte, I haven't tried less then 256 bytes |
2329 | yet). When this function returns, you may | 2329 | yet). When this function returns, you may |
2330 | want to display any rows that were generated | 2330 | want to display any rows that were generated |
2331 | in the row callback if you don't already do | 2331 | in the row callback if you don't already do |
2332 | so there. | 2332 | so there. |
2333 | */ | 2333 | */ |
2334 | png_process_data(png_ptr, info_ptr, buffer, length); | 2334 | png_process_data(png_ptr, info_ptr, buffer, length); |
2335 | 2335 | ||
2336 | /* At this point you can call png_process_data_skip if | 2336 | /* At this point you can call png_process_data_skip if |
2337 | you want to handle data the library will skip yourself; | 2337 | you want to handle data the library will skip yourself; |
2338 | it simply returns the number of bytes to skip (and stops | 2338 | it simply returns the number of bytes to skip (and stops |
2339 | libpng skipping that number of bytes on the next | 2339 | libpng skipping that number of bytes on the next |
2340 | png_process_data call). | 2340 | png_process_data call). |
2341 | return 0; | 2341 | return 0; |
2342 | } | 2342 | } |
2343 | 2343 | ||
2344 | /* This function is called (as set by | 2344 | /* This function is called (as set by |
2345 | png_set_progressive_read_fn() above) when enough data | 2345 | png_set_progressive_read_fn() above) when enough data |
2346 | has been supplied so all of the header has been | 2346 | has been supplied so all of the header has been |
2347 | read. | 2347 | read. |
2348 | */ | 2348 | */ |
2349 | void | 2349 | void |
2350 | info_callback(png_structp png_ptr, png_infop info) | 2350 | info_callback(png_structp png_ptr, png_infop info) |
2351 | { | 2351 | { |
2352 | /* Do any setup here, including setting any of | 2352 | /* Do any setup here, including setting any of |
2353 | the transformations mentioned in the Reading | 2353 | the transformations mentioned in the Reading |
2354 | PNG files section. For now, you _must_ call | 2354 | PNG files section. For now, you _must_ call |
2355 | either png_start_read_image() or | 2355 | either png_start_read_image() or |
2356 | png_read_update_info() after all the | 2356 | png_read_update_info() after all the |
2357 | transformations are set (even if you don't set | 2357 | transformations are set (even if you don't set |
2358 | any). You may start getting rows before | 2358 | any). You may start getting rows before |
2359 | png_process_data() returns, so this is your | 2359 | png_process_data() returns, so this is your |
2360 | last chance to prepare for that. | 2360 | last chance to prepare for that. |
2361 | 2361 | ||
2362 | This is where you turn on interlace handling, | 2362 | This is where you turn on interlace handling, |
2363 | assuming you don't want to do it yourself. | 2363 | assuming you don't want to do it yourself. |
2364 | 2364 | ||
2365 | If you need to you can stop the processing of | 2365 | If you need to you can stop the processing of |
2366 | your original input data at this point by calling | 2366 | your original input data at this point by calling |
2367 | png_process_data_pause. This returns the number | 2367 | png_process_data_pause. This returns the number |
2368 | of unprocessed bytes from the last png_process_data | 2368 | of unprocessed bytes from the last png_process_data |
2369 | call - it is up to you to ensure that the next call | 2369 | call - it is up to you to ensure that the next call |
2370 | sees these bytes again. If you don't want to bother | 2370 | sees these bytes again. If you don't want to bother |
2371 | with this you can get libpng to cache the unread | 2371 | with this you can get libpng to cache the unread |
2372 | bytes by setting the 'save' parameter (see png.h) but | 2372 | bytes by setting the 'save' parameter (see png.h) but |
2373 | then libpng will have to copy the data internally. | 2373 | then libpng will have to copy the data internally. |
2374 | */ | 2374 | */ |
2375 | } | 2375 | } |
2376 | 2376 | ||
2377 | /* This function is called when each row of image | 2377 | /* This function is called when each row of image |
2378 | data is complete */ | 2378 | data is complete */ |
2379 | void | 2379 | void |
2380 | row_callback(png_structp png_ptr, png_bytep new_row, | 2380 | row_callback(png_structp png_ptr, png_bytep new_row, |
2381 | png_uint_32 row_num, int pass) | 2381 | png_uint_32 row_num, int pass) |
2382 | { | 2382 | { |
2383 | /* If the image is interlaced, and you turned | 2383 | /* If the image is interlaced, and you turned |
2384 | on the interlace handler, this function will | 2384 | on the interlace handler, this function will |
2385 | be called for every row in every pass. Some | 2385 | be called for every row in every pass. Some |
2386 | of these rows will not be changed from the | 2386 | of these rows will not be changed from the |
2387 | previous pass. When the row is not changed, | 2387 | previous pass. When the row is not changed, |
2388 | the new_row variable will be NULL. The rows | 2388 | the new_row variable will be NULL. The rows |
2389 | and passes are called in order, so you don't | 2389 | and passes are called in order, so you don't |
2390 | really need the row_num and pass, but I'm | 2390 | really need the row_num and pass, but I'm |
2391 | supplying them because it may make your life | 2391 | supplying them because it may make your life |
2392 | easier. | 2392 | easier. |
2393 | 2393 | ||
2394 | If you did not turn on interlace handling then | 2394 | If you did not turn on interlace handling then |
2395 | the callback is called for each row of each | 2395 | the callback is called for each row of each |
2396 | sub-image when the image is interlaced. In this | 2396 | sub-image when the image is interlaced. In this |
2397 | case 'row_num' is the row in the sub-image, not | 2397 | case 'row_num' is the row in the sub-image, not |
2398 | the row in the output image as it is in all other | 2398 | the row in the output image as it is in all other |
2399 | cases. | 2399 | cases. |
2400 | 2400 | ||
2401 | For the non-NULL rows of interlaced images when | 2401 | For the non-NULL rows of interlaced images when |
2402 | you have switched on libpng interlace handling, | 2402 | you have switched on libpng interlace handling, |
2403 | you must call png_progressive_combine_row() | 2403 | you must call png_progressive_combine_row() |
2404 | passing in the row and the old row. You can | 2404 | passing in the row and the old row. You can |
2405 | call this function for NULL rows (it will just | 2405 | call this function for NULL rows (it will just |
2406 | return) and for non-interlaced images (it just | 2406 | return) and for non-interlaced images (it just |
2407 | does the memcpy for you) if it will make the | 2407 | does the memcpy for you) if it will make the |
2408 | code easier. Thus, you can just do this for | 2408 | code easier. Thus, you can just do this for |
2409 | all cases if you switch on interlace handling; | 2409 | all cases if you switch on interlace handling; |
2410 | */ | 2410 | */ |
2411 | 2411 | ||
2412 | png_progressive_combine_row(png_ptr, old_row, | 2412 | png_progressive_combine_row(png_ptr, old_row, |
2413 | new_row); | 2413 | new_row); |
2414 | 2414 | ||
2415 | /* where old_row is what was displayed for | 2415 | /* where old_row is what was displayed for |
2416 | previously for the row. Note that the first | 2416 | previously for the row. Note that the first |
2417 | pass (pass == 0, really) will completely cover | 2417 | pass (pass == 0, really) will completely cover |
2418 | the old row, so the rows do not have to be | 2418 | the old row, so the rows do not have to be |
2419 | initialized. After the first pass (and only | 2419 | initialized. After the first pass (and only |
2420 | for interlaced images), you will have to pass | 2420 | for interlaced images), you will have to pass |
2421 | the current row, and the function will combine | 2421 | the current row, and the function will combine |
2422 | the old row and the new row. | 2422 | the old row and the new row. |
2423 | 2423 | ||
2424 | You can also call png_process_data_pause in this | 2424 | You can also call png_process_data_pause in this |
2425 | callback - see above. | 2425 | callback - see above. |
2426 | */ | 2426 | */ |
2427 | } | 2427 | } |
2428 | 2428 | ||
2429 | void | 2429 | void |
2430 | end_callback(png_structp png_ptr, png_infop info) | 2430 | end_callback(png_structp png_ptr, png_infop info) |
2431 | { | 2431 | { |
2432 | /* This function is called after the whole image | 2432 | /* This function is called after the whole image |
2433 | has been read, including any chunks after the | 2433 | has been read, including any chunks after the |
2434 | image (up to and including the IEND). You | 2434 | image (up to and including the IEND). You |
2435 | will usually have the same info chunk as you | 2435 | will usually have the same info chunk as you |
2436 | had in the header, although some data may have | 2436 | had in the header, although some data may have |
2437 | been added to the comments and time fields. | 2437 | been added to the comments and time fields. |
2438 | 2438 | ||
2439 | Most people won't do much here, perhaps setting | 2439 | Most people won't do much here, perhaps setting |
2440 | a flag that marks the image as finished. | 2440 | a flag that marks the image as finished. |
2441 | */ | 2441 | */ |
2442 | } | 2442 | } |
2443 | 2443 | ||
2444 | 2444 | ||
2445 | 2445 | ||
2446 | IV. Writing | 2446 | IV. Writing |
2447 | 2447 | ||
2448 | Much of this is very similar to reading. However, everything of | 2448 | Much of this is very similar to reading. However, everything of |
2449 | importance is repeated here, so you won't have to constantly look | 2449 | importance is repeated here, so you won't have to constantly look |
2450 | back up in the reading section to understand writing. | 2450 | back up in the reading section to understand writing. |
2451 | 2451 | ||
2452 | Setup | 2452 | Setup |
2453 | 2453 | ||
2454 | You will want to do the I/O initialization before you get into libpng, | 2454 | You will want to do the I/O initialization before you get into libpng, |
2455 | so if it doesn't work, you don't have anything to undo. If you are not | 2455 | so if it doesn't work, you don't have anything to undo. If you are not |
2456 | using the standard I/O functions, you will need to replace them with | 2456 | using the standard I/O functions, you will need to replace them with |
2457 | custom writing functions. See the discussion under Customizing libpng. | 2457 | custom writing functions. See the discussion under Customizing libpng. |
2458 | 2458 | ||
2459 | FILE *fp = fopen(file_name, "wb"); | 2459 | FILE *fp = fopen(file_name, "wb"); |
2460 | 2460 | ||
2461 | if (!fp) | 2461 | if (!fp) |
2462 | return (ERROR); | 2462 | return (ERROR); |
2463 | 2463 | ||
2464 | Next, png_struct and png_info need to be allocated and initialized. | 2464 | Next, png_struct and png_info need to be allocated and initialized. |
2465 | As these can be both relatively large, you may not want to store these | 2465 | As these can be both relatively large, you may not want to store these |
2466 | on the stack, unless you have stack space to spare. Of course, you | 2466 | on the stack, unless you have stack space to spare. Of course, you |
2467 | will want to check if they return NULL. If you are also reading, | 2467 | will want to check if they return NULL. If you are also reading, |
2468 | you won't want to name your read structure and your write structure | 2468 | you won't want to name your read structure and your write structure |
2469 | both "png_ptr"; you can call them anything you like, such as | 2469 | both "png_ptr"; you can call them anything you like, such as |
2470 | "read_ptr" and "write_ptr". Look at pngtest.c, for example. | 2470 | "read_ptr" and "write_ptr". Look at pngtest.c, for example. |
2471 | 2471 | ||
2472 | png_structp png_ptr = png_create_write_struct | 2472 | png_structp png_ptr = png_create_write_struct |
2473 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | 2473 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, |
2474 | user_error_fn, user_warning_fn); | 2474 | user_error_fn, user_warning_fn); |
2475 | 2475 | ||
2476 | if (!png_ptr) | 2476 | if (!png_ptr) |
2477 | return (ERROR); | 2477 | return (ERROR); |
2478 | 2478 | ||
2479 | png_infop info_ptr = png_create_info_struct(png_ptr); | 2479 | png_infop info_ptr = png_create_info_struct(png_ptr); |
2480 | if (!info_ptr) | 2480 | if (!info_ptr) |
2481 | { | 2481 | { |
2482 | png_destroy_write_struct(&png_ptr, | 2482 | png_destroy_write_struct(&png_ptr, |
2483 | (png_infopp)NULL); | 2483 | (png_infopp)NULL); |
2484 | return (ERROR); | 2484 | return (ERROR); |
2485 | } | 2485 | } |
2486 | 2486 | ||
2487 | If you want to use your own memory allocation routines, | 2487 | If you want to use your own memory allocation routines, |
2488 | define PNG_USER_MEM_SUPPORTED and use | 2488 | define PNG_USER_MEM_SUPPORTED and use |
2489 | png_create_write_struct_2() instead of png_create_write_struct(): | 2489 | png_create_write_struct_2() instead of png_create_write_struct(): |
2490 | 2490 | ||
2491 | png_structp png_ptr = png_create_write_struct_2 | 2491 | png_structp png_ptr = png_create_write_struct_2 |
2492 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, | 2492 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr, |
2493 | user_error_fn, user_warning_fn, (png_voidp) | 2493 | user_error_fn, user_warning_fn, (png_voidp) |
2494 | user_mem_ptr, user_malloc_fn, user_free_fn); | 2494 | user_mem_ptr, user_malloc_fn, user_free_fn); |
2495 | 2495 | ||
2496 | After you have these structures, you will need to set up the | 2496 | After you have these structures, you will need to set up the |
2497 | error handling. When libpng encounters an error, it expects to | 2497 | error handling. When libpng encounters an error, it expects to |
2498 | longjmp() back to your routine. Therefore, you will need to call | 2498 | longjmp() back to your routine. Therefore, you will need to call |
2499 | setjmp() and pass the png_jmpbuf(png_ptr). If you | 2499 | setjmp() and pass the png_jmpbuf(png_ptr). If you |
2500 | write the file from different routines, you will need to update | 2500 | write the file from different routines, you will need to update |
2501 | the png_jmpbuf(png_ptr) every time you enter a new routine that will | 2501 | the png_jmpbuf(png_ptr) every time you enter a new routine that will |
2502 | call a png_*() function. See your documentation of setjmp/longjmp | 2502 | call a png_*() function. See your documentation of setjmp/longjmp |
2503 | for your compiler for more information on setjmp/longjmp. See | 2503 | for your compiler for more information on setjmp/longjmp. See |
2504 | the discussion on libpng error handling in the Customizing Libpng | 2504 | the discussion on libpng error handling in the Customizing Libpng |
2505 | section below for more information on the libpng error handling. | 2505 | section below for more information on the libpng error handling. |
2506 | 2506 | ||
2507 | if (setjmp(png_jmpbuf(png_ptr))) | 2507 | if (setjmp(png_jmpbuf(png_ptr))) |
2508 | { | 2508 | { |
2509 | png_destroy_write_struct(&png_ptr, &info_ptr); | 2509 | png_destroy_write_struct(&png_ptr, &info_ptr); |
2510 | fclose(fp); | 2510 | fclose(fp); |
2511 | return (ERROR); | 2511 | return (ERROR); |
2512 | } | 2512 | } |
2513 | ... | 2513 | ... |
2514 | return; | 2514 | return; |
2515 | 2515 | ||
2516 | If you would rather avoid the complexity of setjmp/longjmp issues, | 2516 | If you would rather avoid the complexity of setjmp/longjmp issues, |
2517 | you can compile libpng with PNG_NO_SETJMP, in which case | 2517 | you can compile libpng with PNG_NO_SETJMP, in which case |
2518 | errors will result in a call to PNG_ABORT() which defaults to abort(). | 2518 | errors will result in a call to PNG_ABORT() which defaults to abort(). |
2519 | 2519 | ||
2520 | You can #define PNG_ABORT() to a function that does something | 2520 | You can #define PNG_ABORT() to a function that does something |
2521 | more useful than abort(), as long as your function does not | 2521 | more useful than abort(), as long as your function does not |
2522 | return. | 2522 | return. |
2523 | 2523 | ||
2524 | Now you need to set up the output code. The default for libpng is to | 2524 | Now you need to set up the output code. The default for libpng is to |
2525 | use the C function fwrite(). If you use this, you will need to pass a | 2525 | use the C function fwrite(). If you use this, you will need to pass a |
2526 | valid FILE * in the function png_init_io(). Be sure that the file is | 2526 | valid FILE * in the function png_init_io(). Be sure that the file is |
2527 | opened in binary mode. Again, if you wish to handle writing data in | 2527 | opened in binary mode. Again, if you wish to handle writing data in |
2528 | another way, see the discussion on libpng I/O handling in the Customizing | 2528 | another way, see the discussion on libpng I/O handling in the Customizing |
2529 | Libpng section below. | 2529 | Libpng section below. |
2530 | 2530 | ||
2531 | png_init_io(png_ptr, fp); | 2531 | png_init_io(png_ptr, fp); |
2532 | 2532 | ||
2533 | If you are embedding your PNG into a datastream such as MNG, and don't | 2533 | If you are embedding your PNG into a datastream such as MNG, and don't |
2534 | want libpng to write the 8-byte signature, or if you have already | 2534 | want libpng to write the 8-byte signature, or if you have already |
2535 | written the signature in your application, use | 2535 | written the signature in your application, use |
2536 | 2536 | ||
2537 | png_set_sig_bytes(png_ptr, 8); | 2537 | png_set_sig_bytes(png_ptr, 8); |
2538 | 2538 | ||
2539 | to inform libpng that it should not write a signature. | 2539 | to inform libpng that it should not write a signature. |
2540 | 2540 | ||
2541 | Write callbacks | 2541 | Write callbacks |
2542 | 2542 | ||
2543 | At this point, you can set up a callback function that will be | 2543 | At this point, you can set up a callback function that will be |
2544 | called after each row has been written, which you can use to control | 2544 | called after each row has been written, which you can use to control |
2545 | a progress meter or the like. It's demonstrated in pngtest.c. | 2545 | a progress meter or the like. It's demonstrated in pngtest.c. |
2546 | You must supply a function | 2546 | You must supply a function |
2547 | 2547 | ||
2548 | void write_row_callback(png_structp png_ptr, png_uint_32 row, | 2548 | void write_row_callback(png_structp png_ptr, png_uint_32 row, |
2549 | int pass); | 2549 | int pass); |
2550 | { | 2550 | { |
2551 | /* put your code here */ | 2551 | /* put your code here */ |
2552 | } | 2552 | } |
2553 | 2553 | ||
2554 | (You can give it another name that you like instead of "write_row_callback") | 2554 | (You can give it another name that you like instead of "write_row_callback") |
2555 | 2555 | ||
2556 | To inform libpng about your function, use | 2556 | To inform libpng about your function, use |
2557 | 2557 | ||
2558 | png_set_write_status_fn(png_ptr, write_row_callback); | 2558 | png_set_write_status_fn(png_ptr, write_row_callback); |
2559 | 2559 | ||
2560 | When this function is called the row has already been completely processed and | 2560 | When this function is called the row has already been completely processed and |
2561 | it has also been written out. The 'row' and 'pass' refer to the next row to be | 2561 | it has also been written out. The 'row' and 'pass' refer to the next row to be |
2562 | handled. For the | 2562 | handled. For the |
2563 | non-interlaced case the row that was just handled is simply one less than the | 2563 | non-interlaced case the row that was just handled is simply one less than the |
2564 | passed in row number, and pass will always be 0. For the interlaced case the | 2564 | passed in row number, and pass will always be 0. For the interlaced case the |
2565 | same applies unless the row value is 0, in which case the row just handled was | 2565 | same applies unless the row value is 0, in which case the row just handled was |
2566 | the last one from one of the preceding passes. Because interlacing may skip a | 2566 | the last one from one of the preceding passes. Because interlacing may skip a |
2567 | pass you cannot be sure that the preceding pass is just 'pass-1', if you really | 2567 | pass you cannot be sure that the preceding pass is just 'pass-1', if you really |
2568 | need to know what the last pass is record (row,pass) from the callback and use | 2568 | need to know what the last pass is record (row,pass) from the callback and use |
2569 | the last recorded value each time. | 2569 | the last recorded value each time. |
2570 | 2570 | ||
2571 | As with the user transform you can find the output row using the | 2571 | As with the user transform you can find the output row using the |
2572 | PNG_ROW_FROM_PASS_ROW macro. | 2572 | PNG_ROW_FROM_PASS_ROW macro. |
2573 | 2573 | ||
2574 | You now have the option of modifying how the compression library will | 2574 | You now have the option of modifying how the compression library will |
2575 | run. The following functions are mainly for testing, but may be useful | 2575 | run. The following functions are mainly for testing, but may be useful |
2576 | in some cases, like if you need to write PNG files extremely fast and | 2576 | in some cases, like if you need to write PNG files extremely fast and |
2577 | are willing to give up some compression, or if you want to get the | 2577 | are willing to give up some compression, or if you want to get the |
2578 | maximum possible compression at the expense of slower writing. If you | 2578 | maximum possible compression at the expense of slower writing. If you |
2579 | have no special needs in this area, let the library do what it wants by | 2579 | have no special needs in this area, let the library do what it wants by |
2580 | not calling this function at all, as it has been tuned to deliver a good | 2580 | not calling this function at all, as it has been tuned to deliver a good |
2581 | speed/compression ratio. The second parameter to png_set_filter() is | 2581 | speed/compression ratio. The second parameter to png_set_filter() is |
2582 | the filter method, for which the only valid values are 0 (as of the | 2582 | the filter method, for which the only valid values are 0 (as of the |
2583 | July 1999 PNG specification, version 1.2) or 64 (if you are writing | 2583 | July 1999 PNG specification, version 1.2) or 64 (if you are writing |
2584 | a PNG datastream that is to be embedded in a MNG datastream). The third | 2584 | a PNG datastream that is to be embedded in a MNG datastream). The third |
2585 | parameter is a flag that indicates which filter type(s) are to be tested | 2585 | parameter is a flag that indicates which filter type(s) are to be tested |
2586 | for each scanline. See the PNG specification for details on the specific | 2586 | for each scanline. See the PNG specification for details on the specific |
2587 | filter types. | 2587 | filter types. |
2588 | 2588 | ||
2589 | 2589 | ||
2590 | /* turn on or off filtering, and/or choose | 2590 | /* turn on or off filtering, and/or choose |
2591 | specific filters. You can use either a single | 2591 | specific filters. You can use either a single |
2592 | PNG_FILTER_VALUE_NAME or the bitwise OR of one | 2592 | PNG_FILTER_VALUE_NAME or the bitwise OR of one |
2593 | or more PNG_FILTER_NAME masks. | 2593 | or more PNG_FILTER_NAME masks. |
2594 | */ | 2594 | */ |
2595 | png_set_filter(png_ptr, 0, | 2595 | png_set_filter(png_ptr, 0, |
2596 | PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | | 2596 | PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE | |
2597 | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB | | 2597 | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB | |
2598 | PNG_FILTER_UP | PNG_FILTER_VALUE_UP | | 2598 | PNG_FILTER_UP | PNG_FILTER_VALUE_UP | |
2599 | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG | | 2599 | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG | |
2600 | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH| | 2600 | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH| |
2601 | PNG_ALL_FILTERS); | 2601 | PNG_ALL_FILTERS); |
2602 | 2602 | ||
2603 | If an application wants to start and stop using particular filters during | 2603 | If an application wants to start and stop using particular filters during |
2604 | compression, it should start out with all of the filters (to ensure that | 2604 | compression, it should start out with all of the filters (to ensure that |
2605 | the previous row of pixels will be stored in case it's needed later), | 2605 | the previous row of pixels will be stored in case it's needed later), |
2606 | and then add and remove them after the start of compression. | 2606 | and then add and remove them after the start of compression. |
2607 | 2607 | ||
2608 | If you are writing a PNG datastream that is to be embedded in a MNG | 2608 | If you are writing a PNG datastream that is to be embedded in a MNG |
2609 | datastream, the second parameter can be either 0 or 64. | 2609 | datastream, the second parameter can be either 0 or 64. |
2610 | 2610 | ||
2611 | The png_set_compression_*() functions interface to the zlib compression | 2611 | The png_set_compression_*() functions interface to the zlib compression |
2612 | library, and should mostly be ignored unless you really know what you are | 2612 | library, and should mostly be ignored unless you really know what you are |
2613 | doing. The only generally useful call is png_set_compression_level() | 2613 | doing. The only generally useful call is png_set_compression_level() |
2614 | which changes how much time zlib spends on trying to compress the image | 2614 | which changes how much time zlib spends on trying to compress the image |
2615 | data. See the Compression Library (zlib.h and algorithm.txt, distributed | 2615 | data. See the Compression Library (zlib.h and algorithm.txt, distributed |
2616 | with zlib) for details on the compression levels. | 2616 | with zlib) for details on the compression levels. |
2617 | 2617 | ||
2618 | #include zlib.h | 2618 | #include zlib.h |
2619 | 2619 | ||
2620 | /* Set the zlib compression level */ | 2620 | /* Set the zlib compression level */ |
2621 | png_set_compression_level(png_ptr, | 2621 | png_set_compression_level(png_ptr, |
2622 | Z_BEST_COMPRESSION); | 2622 | Z_BEST_COMPRESSION); |
2623 | 2623 | ||
2624 | /* Set other zlib parameters for compressing IDAT */ | 2624 | /* Set other zlib parameters for compressing IDAT */ |
2625 | png_set_compression_mem_level(png_ptr, 8); | 2625 | png_set_compression_mem_level(png_ptr, 8); |
2626 | png_set_compression_strategy(png_ptr, | 2626 | png_set_compression_strategy(png_ptr, |
2627 | Z_DEFAULT_STRATEGY); | 2627 | Z_DEFAULT_STRATEGY); |
2628 | png_set_compression_window_bits(png_ptr, 15); | 2628 | png_set_compression_window_bits(png_ptr, 15); |
2629 | png_set_compression_method(png_ptr, 8); | 2629 | png_set_compression_method(png_ptr, 8); |
2630 | png_set_compression_buffer_size(png_ptr, 8192) | 2630 | png_set_compression_buffer_size(png_ptr, 8192) |
2631 | 2631 | ||
2632 | /* Set zlib parameters for text compression | 2632 | /* Set zlib parameters for text compression |
2633 | * If you don't call these, the parameters | 2633 | * If you don't call these, the parameters |
2634 | * fall back on those defined for IDAT chunks | 2634 | * fall back on those defined for IDAT chunks |
2635 | */ | 2635 | */ |
2636 | png_set_text_compression_mem_level(png_ptr, 8); | 2636 | png_set_text_compression_mem_level(png_ptr, 8); |
2637 | png_set_text_compression_strategy(png_ptr, | 2637 | png_set_text_compression_strategy(png_ptr, |
2638 | Z_DEFAULT_STRATEGY); | 2638 | Z_DEFAULT_STRATEGY); |
2639 | png_set_text_compression_window_bits(png_ptr, 15); | 2639 | png_set_text_compression_window_bits(png_ptr, 15); |
2640 | png_set_text_compression_method(png_ptr, 8); | 2640 | png_set_text_compression_method(png_ptr, 8); |
2641 | 2641 | ||
2642 | Setting the contents of info for output | 2642 | Setting the contents of info for output |
2643 | 2643 | ||
2644 | You now need to fill in the png_info structure with all the data you | 2644 | You now need to fill in the png_info structure with all the data you |
2645 | wish to write before the actual image. Note that the only thing you | 2645 | wish to write before the actual image. Note that the only thing you |
2646 | are allowed to write after the image is the text chunks and the time | 2646 | are allowed to write after the image is the text chunks and the time |
2647 | chunk (as of PNG Specification 1.2, anyway). See png_write_end() and | 2647 | chunk (as of PNG Specification 1.2, anyway). See png_write_end() and |
2648 | the latest PNG specification for more information on that. If you | 2648 | the latest PNG specification for more information on that. If you |
2649 | wish to write them before the image, fill them in now, and flag that | 2649 | wish to write them before the image, fill them in now, and flag that |
2650 | data as being valid. If you want to wait until after the data, don't | 2650 | data as being valid. If you want to wait until after the data, don't |
2651 | fill them until png_write_end(). For all the fields in png_info and | 2651 | fill them until png_write_end(). For all the fields in png_info and |
2652 | their data types, see png.h. For explanations of what the fields | 2652 | their data types, see png.h. For explanations of what the fields |
2653 | contain, see the PNG specification. | 2653 | contain, see the PNG specification. |
2654 | 2654 | ||
2655 | Some of the more important parts of the png_info are: | 2655 | Some of the more important parts of the png_info are: |
2656 | 2656 | ||
2657 | png_set_IHDR(png_ptr, info_ptr, width, height, | 2657 | png_set_IHDR(png_ptr, info_ptr, width, height, |
2658 | bit_depth, color_type, interlace_type, | 2658 | bit_depth, color_type, interlace_type, |
2659 | compression_type, filter_method) | 2659 | compression_type, filter_method) |
2660 | 2660 | ||
2661 | width - holds the width of the image | 2661 | width - holds the width of the image |
2662 | in pixels (up to 2^31). | 2662 | in pixels (up to 2^31). |
2663 | 2663 | ||
2664 | height - holds the height of the image | 2664 | height - holds the height of the image |
2665 | in pixels (up to 2^31). | 2665 | in pixels (up to 2^31). |
2666 | 2666 | ||
2667 | bit_depth - holds the bit depth of one of the | 2667 | bit_depth - holds the bit depth of one of the |
2668 | image channels. | 2668 | image channels. |
2669 | (valid values are 1, 2, 4, 8, 16 | 2669 | (valid values are 1, 2, 4, 8, 16 |
2670 | and depend also on the | 2670 | and depend also on the |
2671 | color_type. See also significant | 2671 | color_type. See also significant |
2672 | bits (sBIT) below). | 2672 | bits (sBIT) below). |
2673 | 2673 | ||
2674 | color_type - describes which color/alpha | 2674 | color_type - describes which color/alpha |
2675 | channels are present. | 2675 | channels are present. |
2676 | PNG_COLOR_TYPE_GRAY | 2676 | PNG_COLOR_TYPE_GRAY |
2677 | (bit depths 1, 2, 4, 8, 16) | 2677 | (bit depths 1, 2, 4, 8, 16) |
2678 | PNG_COLOR_TYPE_GRAY_ALPHA | 2678 | PNG_COLOR_TYPE_GRAY_ALPHA |
2679 | (bit depths 8, 16) | 2679 | (bit depths 8, 16) |
2680 | PNG_COLOR_TYPE_PALETTE | 2680 | PNG_COLOR_TYPE_PALETTE |
2681 | (bit depths 1, 2, 4, 8) | 2681 | (bit depths 1, 2, 4, 8) |
2682 | PNG_COLOR_TYPE_RGB | 2682 | PNG_COLOR_TYPE_RGB |
2683 | (bit_depths 8, 16) | 2683 | (bit_depths 8, 16) |
2684 | PNG_COLOR_TYPE_RGB_ALPHA | 2684 | PNG_COLOR_TYPE_RGB_ALPHA |
2685 | (bit_depths 8, 16) | 2685 | (bit_depths 8, 16) |
2686 | 2686 | ||
2687 | PNG_COLOR_MASK_PALETTE | 2687 | PNG_COLOR_MASK_PALETTE |
2688 | PNG_COLOR_MASK_COLOR | 2688 | PNG_COLOR_MASK_COLOR |
2689 | PNG_COLOR_MASK_ALPHA | 2689 | PNG_COLOR_MASK_ALPHA |
2690 | 2690 | ||
2691 | interlace_type - PNG_INTERLACE_NONE or | 2691 | interlace_type - PNG_INTERLACE_NONE or |
2692 | PNG_INTERLACE_ADAM7 | 2692 | PNG_INTERLACE_ADAM7 |
2693 | 2693 | ||
2694 | compression_type - (must be | 2694 | compression_type - (must be |
2695 | PNG_COMPRESSION_TYPE_DEFAULT) | 2695 | PNG_COMPRESSION_TYPE_DEFAULT) |
2696 | 2696 | ||
2697 | filter_method - (must be PNG_FILTER_TYPE_DEFAULT | 2697 | filter_method - (must be PNG_FILTER_TYPE_DEFAULT |
2698 | or, if you are writing a PNG to | 2698 | or, if you are writing a PNG to |
2699 | be embedded in a MNG datastream, | 2699 | be embedded in a MNG datastream, |
2700 | can also be | 2700 | can also be |
2701 | PNG_INTRAPIXEL_DIFFERENCING) | 2701 | PNG_INTRAPIXEL_DIFFERENCING) |
2702 | 2702 | ||
2703 | If you call png_set_IHDR(), the call must appear before any of the | 2703 | If you call png_set_IHDR(), the call must appear before any of the |
2704 | other png_set_*() functions, because they might require access to some of | 2704 | other png_set_*() functions, because they might require access to some of |
2705 | the IHDR settings. The remaining png_set_*() functions can be called | 2705 | the IHDR settings. The remaining png_set_*() functions can be called |
2706 | in any order. | 2706 | in any order. |
2707 | 2707 | ||
2708 | If you wish, you can reset the compression_type, interlace_type, or | 2708 | If you wish, you can reset the compression_type, interlace_type, or |
2709 | filter_method later by calling png_set_IHDR() again; if you do this, the | 2709 | filter_method later by calling png_set_IHDR() again; if you do this, the |
2710 | width, height, bit_depth, and color_type must be the same in each call. | 2710 | width, height, bit_depth, and color_type must be the same in each call. |
2711 | 2711 | ||
2712 | png_set_PLTE(png_ptr, info_ptr, palette, | 2712 | png_set_PLTE(png_ptr, info_ptr, palette, |
2713 | num_palette); | 2713 | num_palette); |
2714 | 2714 | ||
2715 | palette - the palette for the file | 2715 | palette - the palette for the file |
2716 | (array of png_color) | 2716 | (array of png_color) |
2717 | num_palette - number of entries in the palette | 2717 | num_palette - number of entries in the palette |
2718 | 2718 | ||
2719 | png_set_gAMA(png_ptr, info_ptr, file_gamma); | 2719 | png_set_gAMA(png_ptr, info_ptr, file_gamma); |
2720 | png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma); | 2720 | png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma); |
2721 | 2721 | ||
2722 | file_gamma - the gamma at which the image was | 2722 | file_gamma - the gamma at which the image was |
2723 | created (PNG_INFO_gAMA) | 2723 | created (PNG_INFO_gAMA) |
2724 | 2724 | ||
2725 | int_file_gamma - 100,000 times the gamma at which | 2725 | int_file_gamma - 100,000 times the gamma at which |
2726 | the image was created | 2726 | the image was created |
2727 | 2727 | ||
2728 | png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y, | 2728 | png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y, |
2729 | green_x, green_y, blue_x, blue_y) | 2729 | green_x, green_y, blue_x, blue_y) |
2730 | png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X, | 2730 | png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X, |
2731 | green_Y, green_Z, blue_X, blue_Y, blue_Z) | 2731 | green_Y, green_Z, blue_X, blue_Y, blue_Z) |
2732 | png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y, | 2732 | png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y, |
2733 | int_red_x, int_red_y, int_green_x, int_green_y, | 2733 | int_red_x, int_red_y, int_green_x, int_green_y, |
2734 | int_blue_x, int_blue_y) | 2734 | int_blue_x, int_blue_y) |
2735 | png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y, | 2735 | png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y, |
2736 | int_red_Z, int_green_X, int_green_Y, int_green_Z, | 2736 | int_red_Z, int_green_X, int_green_Y, int_green_Z, |
2737 | int_blue_X, int_blue_Y, int_blue_Z) | 2737 | int_blue_X, int_blue_Y, int_blue_Z) |
2738 | 2738 | ||
2739 | {white,red,green,blue}_{x,y} | 2739 | {white,red,green,blue}_{x,y} |
2740 | A color space encoding specified using the chromaticities | 2740 | A color space encoding specified using the chromaticities |
2741 | of the end points and the white point. | 2741 | of the end points and the white point. |
2742 | 2742 | ||
2743 | {red,green,blue}_{X,Y,Z} | 2743 | {red,green,blue}_{X,Y,Z} |
2744 | A color space encoding specified using the encoding end | 2744 | A color space encoding specified using the encoding end |
2745 | points - the CIE tristimulus specification of the intended | 2745 | points - the CIE tristimulus specification of the intended |
2746 | color of the red, green and blue channels in the PNG RGB | 2746 | color of the red, green and blue channels in the PNG RGB |
2747 | data. The white point is simply the sum of the three end | 2747 | data. The white point is simply the sum of the three end |
2748 | points. | 2748 | points. |
2749 | 2749 | ||
2750 | png_set_sRGB(png_ptr, info_ptr, srgb_intent); | 2750 | png_set_sRGB(png_ptr, info_ptr, srgb_intent); |
2751 | 2751 | ||
2752 | srgb_intent - the rendering intent | 2752 | srgb_intent - the rendering intent |
2753 | (PNG_INFO_sRGB) The presence of | 2753 | (PNG_INFO_sRGB) The presence of |
2754 | the sRGB chunk means that the pixel | 2754 | the sRGB chunk means that the pixel |
2755 | data is in the sRGB color space. | 2755 | data is in the sRGB color space. |
2756 | This chunk also implies specific | 2756 | This chunk also implies specific |
2757 | values of gAMA and cHRM. Rendering | 2757 | values of gAMA and cHRM. Rendering |
2758 | intent is the CSS-1 property that | 2758 | intent is the CSS-1 property that |
2759 | has been defined by the International | 2759 | has been defined by the International |
2760 | Color Consortium | 2760 | Color Consortium |
2761 | (http://www.color.org). | 2761 | (http://www.color.org). |
2762 | It can be one of | 2762 | It can be one of |
2763 | PNG_sRGB_INTENT_SATURATION, | 2763 | PNG_sRGB_INTENT_SATURATION, |
2764 | PNG_sRGB_INTENT_PERCEPTUAL, | 2764 | PNG_sRGB_INTENT_PERCEPTUAL, |
2765 | PNG_sRGB_INTENT_ABSOLUTE, or | 2765 | PNG_sRGB_INTENT_ABSOLUTE, or |
2766 | PNG_sRGB_INTENT_RELATIVE. | 2766 | PNG_sRGB_INTENT_RELATIVE. |
2767 | 2767 | ||
2768 | 2768 | ||
2769 | png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, | 2769 | png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr, |
2770 | srgb_intent); | 2770 | srgb_intent); |
2771 | 2771 | ||
2772 | srgb_intent - the rendering intent | 2772 | srgb_intent - the rendering intent |
2773 | (PNG_INFO_sRGB) The presence of the | 2773 | (PNG_INFO_sRGB) The presence of the |
2774 | sRGB chunk means that the pixel | 2774 | sRGB chunk means that the pixel |
2775 | data is in the sRGB color space. | 2775 | data is in the sRGB color space. |
2776 | This function also causes gAMA and | 2776 | This function also causes gAMA and |
2777 | cHRM chunks with the specific values | 2777 | cHRM chunks with the specific values |
2778 | that are consistent with sRGB to be | 2778 | that are consistent with sRGB to be |
2779 | written. | 2779 | written. |
2780 | 2780 | ||
2781 | png_set_iCCP(png_ptr, info_ptr, name, compression_type, | 2781 | png_set_iCCP(png_ptr, info_ptr, name, compression_type, |
2782 | profile, proflen); | 2782 | profile, proflen); |
2783 | 2783 | ||
2784 | name - The profile name. | 2784 | name - The profile name. |
2785 | 2785 | ||
2786 | compression_type - The compression type; always | 2786 | compression_type - The compression type; always |
2787 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. | 2787 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0. |
2788 | You may give NULL to this argument to | 2788 | You may give NULL to this argument to |
2789 | ignore it. | 2789 | ignore it. |
2790 | 2790 | ||
2791 | profile - International Color Consortium color | 2791 | profile - International Color Consortium color |
2792 | profile data. May contain NULs. | 2792 | profile data. May contain NULs. |
2793 | 2793 | ||
2794 | proflen - length of profile data in bytes. | 2794 | proflen - length of profile data in bytes. |
2795 | 2795 | ||
2796 | png_set_sBIT(png_ptr, info_ptr, sig_bit); | 2796 | png_set_sBIT(png_ptr, info_ptr, sig_bit); |
2797 | 2797 | ||
2798 | sig_bit - the number of significant bits for | 2798 | sig_bit - the number of significant bits for |
2799 | (PNG_INFO_sBIT) each of the gray, red, | 2799 | (PNG_INFO_sBIT) each of the gray, red, |
2800 | green, and blue channels, whichever are | 2800 | green, and blue channels, whichever are |
2801 | appropriate for the given color type | 2801 | appropriate for the given color type |
2802 | (png_color_16) | 2802 | (png_color_16) |
2803 | 2803 | ||
2804 | png_set_tRNS(png_ptr, info_ptr, trans_alpha, | 2804 | png_set_tRNS(png_ptr, info_ptr, trans_alpha, |
2805 | num_trans, trans_color); | 2805 | num_trans, trans_color); |
2806 | 2806 | ||
2807 | trans_alpha - array of alpha (transparency) | 2807 | trans_alpha - array of alpha (transparency) |
2808 | entries for palette (PNG_INFO_tRNS) | 2808 | entries for palette (PNG_INFO_tRNS) |
2809 | 2809 | ||
2810 | num_trans - number of transparent entries | 2810 | num_trans - number of transparent entries |
2811 | (PNG_INFO_tRNS) | 2811 | (PNG_INFO_tRNS) |
2812 | 2812 | ||
2813 | trans_color - graylevel or color sample values | 2813 | trans_color - graylevel or color sample values |
2814 | (in order red, green, blue) of the | 2814 | (in order red, green, blue) of the |
2815 | single transparent color for | 2815 | single transparent color for |
2816 | non-paletted images (PNG_INFO_tRNS) | 2816 | non-paletted images (PNG_INFO_tRNS) |
2817 | 2817 | ||
2818 | png_set_hIST(png_ptr, info_ptr, hist); | 2818 | png_set_hIST(png_ptr, info_ptr, hist); |
2819 | 2819 | ||
2820 | hist - histogram of palette (array of | 2820 | hist - histogram of palette (array of |
2821 | png_uint_16) (PNG_INFO_hIST) | 2821 | png_uint_16) (PNG_INFO_hIST) |
2822 | 2822 | ||
2823 | png_set_tIME(png_ptr, info_ptr, mod_time); | 2823 | png_set_tIME(png_ptr, info_ptr, mod_time); |
2824 | 2824 | ||
2825 | mod_time - time image was last modified | 2825 | mod_time - time image was last modified |
2826 | (PNG_VALID_tIME) | 2826 | (PNG_VALID_tIME) |
2827 | 2827 | ||
2828 | png_set_bKGD(png_ptr, info_ptr, background); | 2828 | png_set_bKGD(png_ptr, info_ptr, background); |
2829 | 2829 | ||
2830 | background - background color (of type | 2830 | background - background color (of type |
2831 | png_color_16p) (PNG_VALID_bKGD) | 2831 | png_color_16p) (PNG_VALID_bKGD) |
2832 | 2832 | ||
2833 | png_set_text(png_ptr, info_ptr, text_ptr, num_text); | 2833 | png_set_text(png_ptr, info_ptr, text_ptr, num_text); |
2834 | 2834 | ||
2835 | text_ptr - array of png_text holding image | 2835 | text_ptr - array of png_text holding image |
2836 | comments | 2836 | comments |
2837 | 2837 | ||
2838 | text_ptr[i].compression - type of compression used | 2838 | text_ptr[i].compression - type of compression used |
2839 | on "text" PNG_TEXT_COMPRESSION_NONE | 2839 | on "text" PNG_TEXT_COMPRESSION_NONE |
2840 | PNG_TEXT_COMPRESSION_zTXt | 2840 | PNG_TEXT_COMPRESSION_zTXt |
2841 | PNG_ITXT_COMPRESSION_NONE | 2841 | PNG_ITXT_COMPRESSION_NONE |
2842 | PNG_ITXT_COMPRESSION_zTXt | 2842 | PNG_ITXT_COMPRESSION_zTXt |
2843 | text_ptr[i].key - keyword for comment. Must contain | 2843 | text_ptr[i].key - keyword for comment. Must contain |
2844 | 1-79 characters. | 2844 | 1-79 characters. |
2845 | text_ptr[i].text - text comments for current | 2845 | text_ptr[i].text - text comments for current |
2846 | keyword. Can be NULL or empty. | 2846 | keyword. Can be NULL or empty. |
2847 | text_ptr[i].text_length - length of text string, | 2847 | text_ptr[i].text_length - length of text string, |
2848 | after decompression, 0 for iTXt | 2848 | after decompression, 0 for iTXt |
2849 | text_ptr[i].itxt_length - length of itxt string, | 2849 | text_ptr[i].itxt_length - length of itxt string, |
2850 | after decompression, 0 for tEXt/zTXt | 2850 | after decompression, 0 for tEXt/zTXt |
2851 | text_ptr[i].lang - language of comment (NULL or | 2851 | text_ptr[i].lang - language of comment (NULL or |
2852 | empty for unknown). | 2852 | empty for unknown). |
2853 | text_ptr[i].translated_keyword - keyword in UTF-8 (NULL | 2853 | text_ptr[i].translated_keyword - keyword in UTF-8 (NULL |
2854 | or empty for unknown). | 2854 | or empty for unknown). |
2855 | 2855 | ||
2856 | Note that the itxt_length, lang, and lang_key | 2856 | Note that the itxt_length, lang, and lang_key |
2857 | members of the text_ptr structure only exist when the | 2857 | members of the text_ptr structure only exist when the |
2858 | library is built with iTXt chunk support. Prior to | 2858 | library is built with iTXt chunk support. Prior to |
2859 | libpng-1.4.0 the library was built by default without | 2859 | libpng-1.4.0 the library was built by default without |
2860 | iTXt support. Also note that when iTXt is supported, | 2860 | iTXt support. Also note that when iTXt is supported, |
2861 | they contain NULL pointers when the "compression" | 2861 | they contain NULL pointers when the "compression" |
2862 | field contains PNG_TEXT_COMPRESSION_NONE or | 2862 | field contains PNG_TEXT_COMPRESSION_NONE or |
2863 | PNG_TEXT_COMPRESSION_zTXt. | 2863 | PNG_TEXT_COMPRESSION_zTXt. |
2864 | 2864 | ||
2865 | num_text - number of comments | 2865 | num_text - number of comments |
2866 | 2866 | ||
2867 | png_set_sPLT(png_ptr, info_ptr, &palette_ptr, | 2867 | png_set_sPLT(png_ptr, info_ptr, &palette_ptr, |
2868 | num_spalettes); | 2868 | num_spalettes); |
2869 | 2869 | ||
2870 | palette_ptr - array of png_sPLT_struct structures | 2870 | palette_ptr - array of png_sPLT_struct structures |
2871 | to be added to the list of palettes | 2871 | to be added to the list of palettes |
2872 | in the info structure. | 2872 | in the info structure. |
2873 | num_spalettes - number of palette structures to be | 2873 | num_spalettes - number of palette structures to be |
2874 | added. | 2874 | added. |
2875 | 2875 | ||
2876 | png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, | 2876 | png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y, |
2877 | unit_type); | 2877 | unit_type); |
2878 | 2878 | ||
2879 | offset_x - positive offset from the left | 2879 | offset_x - positive offset from the left |
2880 | edge of the screen | 2880 | edge of the screen |
2881 | 2881 | ||
2882 | offset_y - positive offset from the top | 2882 | offset_y - positive offset from the top |
2883 | edge of the screen | 2883 | edge of the screen |
2884 | 2884 | ||
2885 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER | 2885 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER |
2886 | 2886 | ||
2887 | png_set_pHYs(png_ptr, info_ptr, res_x, res_y, | 2887 | png_set_pHYs(png_ptr, info_ptr, res_x, res_y, |
2888 | unit_type); | 2888 | unit_type); |
2889 | 2889 | ||
2890 | res_x - pixels/unit physical resolution | 2890 | res_x - pixels/unit physical resolution |
2891 | in x direction | 2891 | in x direction |
2892 | 2892 | ||
2893 | res_y - pixels/unit physical resolution | 2893 | res_y - pixels/unit physical resolution |
2894 | in y direction | 2894 | in y direction |
2895 | 2895 | ||
2896 | unit_type - PNG_RESOLUTION_UNKNOWN, | 2896 | unit_type - PNG_RESOLUTION_UNKNOWN, |
2897 | PNG_RESOLUTION_METER | 2897 | PNG_RESOLUTION_METER |
2898 | 2898 | ||
2899 | png_set_sCAL(png_ptr, info_ptr, unit, width, height) | 2899 | png_set_sCAL(png_ptr, info_ptr, unit, width, height) |
2900 | 2900 | ||
2901 | unit - physical scale units (an integer) | 2901 | unit - physical scale units (an integer) |
2902 | 2902 | ||
2903 | width - width of a pixel in physical scale units | 2903 | width - width of a pixel in physical scale units |
2904 | 2904 | ||
2905 | height - height of a pixel in physical scale units | 2905 | height - height of a pixel in physical scale units |
2906 | (width and height are doubles) | 2906 | (width and height are doubles) |
2907 | 2907 | ||
2908 | png_set_sCAL_s(png_ptr, info_ptr, unit, width, height) | 2908 | png_set_sCAL_s(png_ptr, info_ptr, unit, width, height) |
2909 | 2909 | ||
2910 | unit - physical scale units (an integer) | 2910 | unit - physical scale units (an integer) |
2911 | 2911 | ||
2912 | width - width of a pixel in physical scale units | 2912 | width - width of a pixel in physical scale units |
2913 | expressed as a string | 2913 | expressed as a string |
2914 | 2914 | ||
2915 | height - height of a pixel in physical scale units | 2915 | height - height of a pixel in physical scale units |
2916 | (width and height are strings like "2.54") | 2916 | (width and height are strings like "2.54") |
2917 | 2917 | ||
2918 | png_set_unknown_chunks(png_ptr, info_ptr, &unknowns, | 2918 | png_set_unknown_chunks(png_ptr, info_ptr, &unknowns, |
2919 | num_unknowns) | 2919 | num_unknowns) |
2920 | 2920 | ||
2921 | unknowns - array of png_unknown_chunk | 2921 | unknowns - array of png_unknown_chunk |
2922 | structures holding unknown chunks | 2922 | structures holding unknown chunks |
2923 | unknowns[i].name - name of unknown chunk | 2923 | unknowns[i].name - name of unknown chunk |
2924 | unknowns[i].data - data of unknown chunk | 2924 | unknowns[i].data - data of unknown chunk |
2925 | unknowns[i].size - size of unknown chunk's data | 2925 | unknowns[i].size - size of unknown chunk's data |
2926 | unknowns[i].location - position to write chunk in file | 2926 | unknowns[i].location - position to write chunk in file |
2927 | 0: do not write chunk | 2927 | 0: do not write chunk |
2928 | PNG_HAVE_IHDR: before PLTE | 2928 | PNG_HAVE_IHDR: before PLTE |
2929 | PNG_HAVE_PLTE: before IDAT | 2929 | PNG_HAVE_PLTE: before IDAT |
2930 | PNG_AFTER_IDAT: after IDAT | 2930 | PNG_AFTER_IDAT: after IDAT |
2931 | 2931 | ||
2932 | The "location" member is set automatically according to | 2932 | The "location" member is set automatically according to |
2933 | what part of the output file has already been written. | 2933 | what part of the output file has already been written. |
2934 | You can change its value after calling png_set_unknown_chunks() | 2934 | You can change its value after calling png_set_unknown_chunks() |
2935 | as demonstrated in pngtest.c. Within each of the "locations", | 2935 | as demonstrated in pngtest.c. Within each of the "locations", |
2936 | the chunks are sequenced according to their position in the | 2936 | the chunks are sequenced according to their position in the |
2937 | structure (that is, the value of "i", which is the order in which | 2937 | structure (that is, the value of "i", which is the order in which |
2938 | the chunk was either read from the input file or defined with | 2938 | the chunk was either read from the input file or defined with |
2939 | png_set_unknown_chunks). | 2939 | png_set_unknown_chunks). |
2940 | 2940 | ||
2941 | A quick word about text and num_text. text is an array of png_text | 2941 | A quick word about text and num_text. text is an array of png_text |
2942 | structures. num_text is the number of valid structures in the array. | 2942 | structures. num_text is the number of valid structures in the array. |
2943 | Each png_text structure holds a language code, a keyword, a text value, | 2943 | Each png_text structure holds a language code, a keyword, a text value, |
2944 | and a compression type. | 2944 | and a compression type. |
2945 | 2945 | ||
2946 | The compression types have the same valid numbers as the compression | 2946 | The compression types have the same valid numbers as the compression |
2947 | types of the image data. Currently, the only valid number is zero. | 2947 | types of the image data. Currently, the only valid number is zero. |
2948 | However, you can store text either compressed or uncompressed, unlike | 2948 | However, you can store text either compressed or uncompressed, unlike |
2949 | images, which always have to be compressed. So if you don't want the | 2949 | images, which always have to be compressed. So if you don't want the |
2950 | text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE. | 2950 | text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE. |
2951 | Because tEXt and zTXt chunks don't have a language field, if you | 2951 | Because tEXt and zTXt chunks don't have a language field, if you |
2952 | specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt | 2952 | specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt |
2953 | any language code or translated keyword will not be written out. | 2953 | any language code or translated keyword will not be written out. |
2954 | 2954 | ||
2955 | Until text gets around a few hundred bytes, it is not worth compressing it. | 2955 | Until text gets around a few hundred bytes, it is not worth compressing it. |
2956 | After the text has been written out to the file, the compression type | 2956 | After the text has been written out to the file, the compression type |
2957 | is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR, | 2957 | is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR, |
2958 | so that it isn't written out again at the end (in case you are calling | 2958 | so that it isn't written out again at the end (in case you are calling |
2959 | png_write_end() with the same struct). | 2959 | png_write_end() with the same struct). |
2960 | 2960 | ||
2961 | The keywords that are given in the PNG Specification are: | 2961 | The keywords that are given in the PNG Specification are: |
2962 | 2962 | ||
2963 | Title Short (one line) title or | 2963 | Title Short (one line) title or |
2964 | caption for image | 2964 | caption for image |
2965 | 2965 | ||
2966 | Author Name of image's creator | 2966 | Author Name of image's creator |
2967 | 2967 | ||
2968 | Description Description of image (possibly long) | 2968 | Description Description of image (possibly long) |
2969 | 2969 | ||
2970 | Copyright Copyright notice | 2970 | Copyright Copyright notice |
2971 | 2971 | ||
2972 | Creation Time Time of original image creation | 2972 | Creation Time Time of original image creation |
2973 | (usually RFC 1123 format, see below) | 2973 | (usually RFC 1123 format, see below) |
2974 | 2974 | ||
2975 | Software Software used to create the image | 2975 | Software Software used to create the image |
2976 | 2976 | ||
2977 | Disclaimer Legal disclaimer | 2977 | Disclaimer Legal disclaimer |
2978 | 2978 | ||
2979 | Warning Warning of nature of content | 2979 | Warning Warning of nature of content |
2980 | 2980 | ||
2981 | Source Device used to create the image | 2981 | Source Device used to create the image |
2982 | 2982 | ||
2983 | Comment Miscellaneous comment; conversion | 2983 | Comment Miscellaneous comment; conversion |
2984 | from other image format | 2984 | from other image format |
2985 | 2985 | ||
2986 | The keyword-text pairs work like this. Keywords should be short | 2986 | The keyword-text pairs work like this. Keywords should be short |
2987 | simple descriptions of what the comment is about. Some typical | 2987 | simple descriptions of what the comment is about. Some typical |
2988 | keywords are found in the PNG specification, as is some recommendations | 2988 | keywords are found in the PNG specification, as is some recommendations |
2989 | on keywords. You can repeat keywords in a file. You can even write | 2989 | on keywords. You can repeat keywords in a file. You can even write |
2990 | some text before the image and some after. For example, you may want | 2990 | some text before the image and some after. For example, you may want |
2991 | to put a description of the image before the image, but leave the | 2991 | to put a description of the image before the image, but leave the |
2992 | disclaimer until after, so viewers working over modem connections | 2992 | disclaimer until after, so viewers working over modem connections |
2993 | don't have to wait for the disclaimer to go over the modem before | 2993 | don't have to wait for the disclaimer to go over the modem before |
2994 | they start seeing the image. Finally, keywords should be full | 2994 | they start seeing the image. Finally, keywords should be full |
2995 | words, not abbreviations. Keywords and text are in the ISO 8859-1 | 2995 | words, not abbreviations. Keywords and text are in the ISO 8859-1 |
2996 | (Latin-1) character set (a superset of regular ASCII) and can not | 2996 | (Latin-1) character set (a superset of regular ASCII) and can not |
2997 | contain NUL characters, and should not contain control or other | 2997 | contain NUL characters, and should not contain control or other |
2998 | unprintable characters. To make the comments widely readable, stick | 2998 | unprintable characters. To make the comments widely readable, stick |
2999 | with basic ASCII, and avoid machine specific character set extensions | 2999 | with basic ASCII, and avoid machine specific character set extensions |
3000 | like the IBM-PC character set. The keyword must be present, but | 3000 | like the IBM-PC character set. The keyword must be present, but |
3001 | you can leave off the text string on non-compressed pairs. | 3001 | you can leave off the text string on non-compressed pairs. |
3002 | Compressed pairs must have a text string, as only the text string | 3002 | Compressed pairs must have a text string, as only the text string |
3003 | is compressed anyway, so the compression would be meaningless. | 3003 | is compressed anyway, so the compression would be meaningless. |
3004 | 3004 | ||
3005 | PNG supports modification time via the png_time structure. Two | 3005 | PNG supports modification time via the png_time structure. Two |
3006 | conversion routines are provided, png_convert_from_time_t() for | 3006 | conversion routines are provided, png_convert_from_time_t() for |
3007 | time_t and png_convert_from_struct_tm() for struct tm. The | 3007 | time_t and png_convert_from_struct_tm() for struct tm. The |
3008 | time_t routine uses gmtime(). You don't have to use either of | 3008 | time_t routine uses gmtime(). You don't have to use either of |
3009 | these, but if you wish to fill in the png_time structure directly, | 3009 | these, but if you wish to fill in the png_time structure directly, |
3010 | you should provide the time in universal time (GMT) if possible | 3010 | you should provide the time in universal time (GMT) if possible |
3011 | instead of your local time. Note that the year number is the full | 3011 | instead of your local time. Note that the year number is the full |
3012 | year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and | 3012 | year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and |
3013 | that months start with 1. | 3013 | that months start with 1. |
3014 | 3014 | ||
3015 | If you want to store the time of the original image creation, you should | 3015 | If you want to store the time of the original image creation, you should |
3016 | use a plain tEXt chunk with the "Creation Time" keyword. This is | 3016 | use a plain tEXt chunk with the "Creation Time" keyword. This is |
3017 | necessary because the "creation time" of a PNG image is somewhat vague, | 3017 | necessary because the "creation time" of a PNG image is somewhat vague, |
3018 | depending on whether you mean the PNG file, the time the image was | 3018 | depending on whether you mean the PNG file, the time the image was |
3019 | created in a non-PNG format, a still photo from which the image was | 3019 | created in a non-PNG format, a still photo from which the image was |
3020 | scanned, or possibly the subject matter itself. In order to facilitate | 3020 | scanned, or possibly the subject matter itself. In order to facilitate |
3021 | machine-readable dates, it is recommended that the "Creation Time" | 3021 | machine-readable dates, it is recommended that the "Creation Time" |
3022 | tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"), | 3022 | tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"), |
3023 | although this isn't a requirement. Unlike the tIME chunk, the | 3023 | although this isn't a requirement. Unlike the tIME chunk, the |
3024 | "Creation Time" tEXt chunk is not expected to be automatically changed | 3024 | "Creation Time" tEXt chunk is not expected to be automatically changed |
3025 | by the software. To facilitate the use of RFC 1123 dates, a function | 3025 | by the software. To facilitate the use of RFC 1123 dates, a function |
3026 | png_convert_to_rfc1123(png_timep) is provided to convert from PNG | 3026 | png_convert_to_rfc1123(png_timep) is provided to convert from PNG |
3027 | time to an RFC 1123 format string. | 3027 | time to an RFC 1123 format string. |
3028 | 3028 | ||
3029 | Writing unknown chunks | 3029 | Writing unknown chunks |
3030 | 3030 | ||
3031 | You can use the png_set_unknown_chunks function to queue up chunks | 3031 | You can use the png_set_unknown_chunks function to queue up chunks |
3032 | for writing. You give it a chunk name, raw data, and a size; that's | 3032 | for writing. You give it a chunk name, raw data, and a size; that's |
3033 | all there is to it. The chunks will be written by the next following | 3033 | all there is to it. The chunks will be written by the next following |
3034 | png_write_info_before_PLTE, png_write_info, or png_write_end function. | 3034 | png_write_info_before_PLTE, png_write_info, or png_write_end function. |
3035 | Any chunks previously read into the info structure's unknown-chunk | 3035 | Any chunks previously read into the info structure's unknown-chunk |
3036 | list will also be written out in a sequence that satisfies the PNG | 3036 | list will also be written out in a sequence that satisfies the PNG |
3037 | specification's ordering rules. | 3037 | specification's ordering rules. |
3038 | 3038 | ||
3039 | The high-level write interface | 3039 | The high-level write interface |
3040 | 3040 | ||
3041 | At this point there are two ways to proceed; through the high-level | 3041 | At this point there are two ways to proceed; through the high-level |
3042 | write interface, or through a sequence of low-level write operations. | 3042 | write interface, or through a sequence of low-level write operations. |
3043 | You can use the high-level interface if your image data is present | 3043 | You can use the high-level interface if your image data is present |
3044 | in the info structure. All defined output | 3044 | in the info structure. All defined output |
3045 | transformations are permitted, enabled by the following masks. | 3045 | transformations are permitted, enabled by the following masks. |
3046 | 3046 | ||
3047 | PNG_TRANSFORM_IDENTITY No transformation | 3047 | PNG_TRANSFORM_IDENTITY No transformation |
3048 | PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples | 3048 | PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples |
3049 | PNG_TRANSFORM_PACKSWAP Change order of packed | 3049 | PNG_TRANSFORM_PACKSWAP Change order of packed |
3050 | pixels to LSB first | 3050 | pixels to LSB first |
3051 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images | 3051 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images |
3052 | PNG_TRANSFORM_SHIFT Normalize pixels to the | 3052 | PNG_TRANSFORM_SHIFT Normalize pixels to the |
3053 | sBIT depth | 3053 | sBIT depth |
3054 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA | 3054 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA |
3055 | to BGRA | 3055 | to BGRA |
3056 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA | 3056 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA |
3057 | to AG | 3057 | to AG |
3058 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity | 3058 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity |
3059 | to transparency | 3059 | to transparency |
3060 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples | 3060 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples |
3061 | PNG_TRANSFORM_STRIP_FILLER Strip out filler | 3061 | PNG_TRANSFORM_STRIP_FILLER Strip out filler |
3062 | bytes (deprecated). | 3062 | bytes (deprecated). |
3063 | PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading | 3063 | PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading |
3064 | filler bytes | 3064 | filler bytes |
3065 | PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing | 3065 | PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing |
3066 | filler bytes | 3066 | filler bytes |
3067 | 3067 | ||
3068 | If you have valid image data in the info structure (you can use | 3068 | If you have valid image data in the info structure (you can use |
3069 | png_set_rows() to put image data in the info structure), simply do this: | 3069 | png_set_rows() to put image data in the info structure), simply do this: |
3070 | 3070 | ||
3071 | png_write_png(png_ptr, info_ptr, png_transforms, NULL) | 3071 | png_write_png(png_ptr, info_ptr, png_transforms, NULL) |
3072 | 3072 | ||
3073 | where png_transforms is an integer containing the bitwise OR of some set of | 3073 | where png_transforms is an integer containing the bitwise OR of some set of |
3074 | transformation flags. This call is equivalent to png_write_info(), | 3074 | transformation flags. This call is equivalent to png_write_info(), |
3075 | followed the set of transformations indicated by the transform mask, | 3075 | followed the set of transformations indicated by the transform mask, |
3076 | then png_write_image(), and finally png_write_end(). | 3076 | then png_write_image(), and finally png_write_end(). |
3077 | 3077 | ||
3078 | (The final parameter of this call is not yet used. Someday it might point | 3078 | (The final parameter of this call is not yet used. Someday it might point |
3079 | to transformation parameters required by some future output transform.) | 3079 | to transformation parameters required by some future output transform.) |
3080 | 3080 | ||
3081 | You must use png_transforms and not call any png_set_transform() functions | 3081 | You must use png_transforms and not call any png_set_transform() functions |
3082 | when you use png_write_png(). | 3082 | when you use png_write_png(). |
3083 | 3083 | ||
3084 | The low-level write interface | 3084 | The low-level write interface |
3085 | 3085 | ||
3086 | If you are going the low-level route instead, you are now ready to | 3086 | If you are going the low-level route instead, you are now ready to |
3087 | write all the file information up to the actual image data. You do | 3087 | write all the file information up to the actual image data. You do |
3088 | this with a call to png_write_info(). | 3088 | this with a call to png_write_info(). |
3089 | 3089 | ||
3090 | png_write_info(png_ptr, info_ptr); | 3090 | png_write_info(png_ptr, info_ptr); |
3091 | 3091 | ||
3092 | Note that there is one transformation you may need to do before | 3092 | Note that there is one transformation you may need to do before |
3093 | png_write_info(). In PNG files, the alpha channel in an image is the | 3093 | png_write_info(). In PNG files, the alpha channel in an image is the |
3094 | level of opacity. If your data is supplied as a level of transparency, | 3094 | level of opacity. If your data is supplied as a level of transparency, |
3095 | you can invert the alpha channel before you write it, so that 0 is | 3095 | you can invert the alpha channel before you write it, so that 0 is |
3096 | fully transparent and 255 (in 8-bit or paletted images) or 65535 | 3096 | fully transparent and 255 (in 8-bit or paletted images) or 65535 |
3097 | (in 16-bit images) is fully opaque, with | 3097 | (in 16-bit images) is fully opaque, with |
3098 | 3098 | ||
3099 | png_set_invert_alpha(png_ptr); | 3099 | png_set_invert_alpha(png_ptr); |
3100 | 3100 | ||
3101 | This must appear before png_write_info() instead of later with the | 3101 | This must appear before png_write_info() instead of later with the |
3102 | other transformations because in the case of paletted images the tRNS | 3102 | other transformations because in the case of paletted images the tRNS |
3103 | chunk data has to be inverted before the tRNS chunk is written. If | 3103 | chunk data has to be inverted before the tRNS chunk is written. If |
3104 | your image is not a paletted image, the tRNS data (which in such cases | 3104 | your image is not a paletted image, the tRNS data (which in such cases |
3105 | represents a single color to be rendered as transparent) won't need to | 3105 | represents a single color to be rendered as transparent) won't need to |
3106 | be changed, and you can safely do this transformation after your | 3106 | be changed, and you can safely do this transformation after your |
3107 | png_write_info() call. | 3107 | png_write_info() call. |
3108 | 3108 | ||
3109 | If you need to write a private chunk that you want to appear before | 3109 | If you need to write a private chunk that you want to appear before |
3110 | the PLTE chunk when PLTE is present, you can write the PNG info in | 3110 | the PLTE chunk when PLTE is present, you can write the PNG info in |
3111 | two steps, and insert code to write your own chunk between them: | 3111 | two steps, and insert code to write your own chunk between them: |
3112 | 3112 | ||
3113 | png_write_info_before_PLTE(png_ptr, info_ptr); | 3113 | png_write_info_before_PLTE(png_ptr, info_ptr); |
3114 | png_set_unknown_chunks(png_ptr, info_ptr, ...); | 3114 | png_set_unknown_chunks(png_ptr, info_ptr, ...); |
3115 | png_write_info(png_ptr, info_ptr); | 3115 | png_write_info(png_ptr, info_ptr); |
3116 | 3116 | ||
3117 | After you've written the file information, you can set up the library | 3117 | After you've written the file information, you can set up the library |
3118 | to handle any special transformations of the image data. The various | 3118 | to handle any special transformations of the image data. The various |
3119 | ways to transform the data will be described in the order that they | 3119 | ways to transform the data will be described in the order that they |
3120 | should occur. This is important, as some of these change the color | 3120 | should occur. This is important, as some of these change the color |
3121 | type and/or bit depth of the data, and some others only work on | 3121 | type and/or bit depth of the data, and some others only work on |
3122 | certain color types and bit depths. Even though each transformation | 3122 | certain color types and bit depths. Even though each transformation |
3123 | checks to see if it has data that it can do something with, you should | 3123 | checks to see if it has data that it can do something with, you should |
3124 | make sure to only enable a transformation if it will be valid for the | 3124 | make sure to only enable a transformation if it will be valid for the |
3125 | data. For example, don't swap red and blue on grayscale data. | 3125 | data. For example, don't swap red and blue on grayscale data. |
3126 | 3126 | ||
3127 | PNG files store RGB pixels packed into 3 or 6 bytes. This code tells | 3127 | PNG files store RGB pixels packed into 3 or 6 bytes. This code tells |
3128 | the library to strip input data that has 4 or 8 bytes per pixel down | 3128 | the library to strip input data that has 4 or 8 bytes per pixel down |
3129 | to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2 | 3129 | to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2 |
3130 | bytes per pixel). | 3130 | bytes per pixel). |
3131 | 3131 | ||
3132 | png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE); | 3132 | png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE); |
3133 | 3133 | ||
3134 | where the 0 is unused, and the location is either PNG_FILLER_BEFORE or | 3134 | where the 0 is unused, and the location is either PNG_FILLER_BEFORE or |
3135 | PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel | 3135 | PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel |
3136 | is stored XRGB or RGBX. | 3136 | is stored XRGB or RGBX. |
3137 | 3137 | ||
3138 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as | 3138 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as |
3139 | they can, resulting in, for example, 8 pixels per byte for 1 bit files. | 3139 | they can, resulting in, for example, 8 pixels per byte for 1 bit files. |
3140 | If the data is supplied at 1 pixel per byte, use this code, which will | 3140 | If the data is supplied at 1 pixel per byte, use this code, which will |
3141 | correctly pack the pixels into a single byte: | 3141 | correctly pack the pixels into a single byte: |
3142 | 3142 | ||
3143 | png_set_packing(png_ptr); | 3143 | png_set_packing(png_ptr); |
3144 | 3144 | ||
3145 | PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your | 3145 | PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your |
3146 | data is of another bit depth, you can write an sBIT chunk into the | 3146 | data is of another bit depth, you can write an sBIT chunk into the |
3147 | file so that decoders can recover the original data if desired. | 3147 | file so that decoders can recover the original data if desired. |
3148 | 3148 | ||
3149 | /* Set the true bit depth of the image data */ | 3149 | /* Set the true bit depth of the image data */ |
3150 | if (color_type & PNG_COLOR_MASK_COLOR) | 3150 | if (color_type & PNG_COLOR_MASK_COLOR) |
3151 | { | 3151 | { |
3152 | sig_bit.red = true_bit_depth; | 3152 | sig_bit.red = true_bit_depth; |
3153 | sig_bit.green = true_bit_depth; | 3153 | sig_bit.green = true_bit_depth; |
3154 | sig_bit.blue = true_bit_depth; | 3154 | sig_bit.blue = true_bit_depth; |
3155 | } | 3155 | } |
3156 | 3156 | ||
3157 | else | 3157 | else |
3158 | { | 3158 | { |
3159 | sig_bit.gray = true_bit_depth; | 3159 | sig_bit.gray = true_bit_depth; |
3160 | } | 3160 | } |
3161 | 3161 | ||
3162 | if (color_type & PNG_COLOR_MASK_ALPHA) | 3162 | if (color_type & PNG_COLOR_MASK_ALPHA) |
3163 | { | 3163 | { |
3164 | sig_bit.alpha = true_bit_depth; | 3164 | sig_bit.alpha = true_bit_depth; |
3165 | } | 3165 | } |
3166 | 3166 | ||
3167 | png_set_sBIT(png_ptr, info_ptr, &sig_bit); | 3167 | png_set_sBIT(png_ptr, info_ptr, &sig_bit); |
3168 | 3168 | ||
3169 | If the data is stored in the row buffer in a bit depth other than | 3169 | If the data is stored in the row buffer in a bit depth other than |
3170 | one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG), | 3170 | one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG), |
3171 | this will scale the values to appear to be the correct bit depth as | 3171 | this will scale the values to appear to be the correct bit depth as |
3172 | is required by PNG. | 3172 | is required by PNG. |
3173 | 3173 | ||
3174 | png_set_shift(png_ptr, &sig_bit); | 3174 | png_set_shift(png_ptr, &sig_bit); |
3175 | 3175 | ||
3176 | PNG files store 16-bit pixels in network byte order (big-endian, | 3176 | PNG files store 16-bit pixels in network byte order (big-endian, |
3177 | ie. most significant bits first). This code would be used if they are | 3177 | ie. most significant bits first). This code would be used if they are |
3178 | supplied the other way (little-endian, i.e. least significant bits | 3178 | supplied the other way (little-endian, i.e. least significant bits |
3179 | first, the way PCs store them): | 3179 | first, the way PCs store them): |
3180 | 3180 | ||
3181 | if (bit_depth > 8) | 3181 | if (bit_depth > 8) |
3182 | png_set_swap(png_ptr); | 3182 | png_set_swap(png_ptr); |
3183 | 3183 | ||
3184 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you | 3184 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you |
3185 | need to change the order the pixels are packed into bytes, you can use: | 3185 | need to change the order the pixels are packed into bytes, you can use: |
3186 | 3186 | ||
3187 | if (bit_depth < 8) | 3187 | if (bit_depth < 8) |
3188 | png_set_packswap(png_ptr); | 3188 | png_set_packswap(png_ptr); |
3189 | 3189 | ||
3190 | PNG files store 3 color pixels in red, green, blue order. This code | 3190 | PNG files store 3 color pixels in red, green, blue order. This code |
3191 | would be used if they are supplied as blue, green, red: | 3191 | would be used if they are supplied as blue, green, red: |
3192 | 3192 | ||
3193 | png_set_bgr(png_ptr); | 3193 | png_set_bgr(png_ptr); |
3194 | 3194 | ||
3195 | PNG files describe monochrome as black being zero and white being | 3195 | PNG files describe monochrome as black being zero and white being |
3196 | one. This code would be used if the pixels are supplied with this reversed | 3196 | one. This code would be used if the pixels are supplied with this reversed |
3197 | (black being one and white being zero): | 3197 | (black being one and white being zero): |
3198 | 3198 | ||
3199 | png_set_invert_mono(png_ptr); | 3199 | png_set_invert_mono(png_ptr); |
3200 | 3200 | ||
3201 | Finally, you can write your own transformation function if none of | 3201 | Finally, you can write your own transformation function if none of |
3202 | the existing ones meets your needs. This is done by setting a callback | 3202 | the existing ones meets your needs. This is done by setting a callback |
3203 | with | 3203 | with |
3204 | 3204 | ||
3205 | png_set_write_user_transform_fn(png_ptr, | 3205 | png_set_write_user_transform_fn(png_ptr, |
3206 | write_transform_fn); | 3206 | write_transform_fn); |
3207 | 3207 | ||
3208 | You must supply the function | 3208 | You must supply the function |
3209 | 3209 | ||
3210 | void write_transform_fn(png_structp png_ptr, png_row_infop | 3210 | void write_transform_fn(png_structp png_ptr, png_row_infop |
3211 | row_info, png_bytep data) | 3211 | row_info, png_bytep data) |
3212 | 3212 | ||
3213 | See pngtest.c for a working example. Your function will be called | 3213 | See pngtest.c for a working example. Your function will be called |
3214 | before any of the other transformations are processed. If supported | 3214 | before any of the other transformations are processed. If supported |
3215 | libpng also supplies an information routine that may be called from | 3215 | libpng also supplies an information routine that may be called from |
3216 | your callback: | 3216 | your callback: |
3217 | 3217 | ||
3218 | png_get_current_row_number(png_ptr); | 3218 | png_get_current_row_number(png_ptr); |
3219 | png_get_current_pass_number(png_ptr); | 3219 | png_get_current_pass_number(png_ptr); |
3220 | 3220 | ||
3221 | This returns the current row passed to the transform. With interlaced | 3221 | This returns the current row passed to the transform. With interlaced |
3222 | images the value returned is the row in the input sub-image image. Use | 3222 | images the value returned is the row in the input sub-image image. Use |
3223 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to | 3223 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to |
3224 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). | 3224 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass). |
3225 | 3225 | ||
3226 | The discussion of interlace handling above contains more information on how to | 3226 | The discussion of interlace handling above contains more information on how to |
3227 | use these values. | 3227 | use these values. |
3228 | 3228 | ||
3229 | You can also set up a pointer to a user structure for use by your | 3229 | You can also set up a pointer to a user structure for use by your |
3230 | callback function. | 3230 | callback function. |
3231 | 3231 | ||
3232 | png_set_user_transform_info(png_ptr, user_ptr, 0, 0); | 3232 | png_set_user_transform_info(png_ptr, user_ptr, 0, 0); |
3233 | 3233 | ||
3234 | The user_channels and user_depth parameters of this function are ignored | 3234 | The user_channels and user_depth parameters of this function are ignored |
3235 | when writing; you can set them to zero as shown. | 3235 | when writing; you can set them to zero as shown. |
3236 | 3236 | ||
3237 | You can retrieve the pointer via the function png_get_user_transform_ptr(). | 3237 | You can retrieve the pointer via the function png_get_user_transform_ptr(). |
3238 | For example: | 3238 | For example: |
3239 | 3239 | ||
3240 | voidp write_user_transform_ptr = | 3240 | voidp write_user_transform_ptr = |
3241 | png_get_user_transform_ptr(png_ptr); | 3241 | png_get_user_transform_ptr(png_ptr); |
3242 | 3242 | ||
3243 | It is possible to have libpng flush any pending output, either manually, | 3243 | It is possible to have libpng flush any pending output, either manually, |
3244 | or automatically after a certain number of lines have been written. To | 3244 | or automatically after a certain number of lines have been written. To |
3245 | flush the output stream a single time call: | 3245 | flush the output stream a single time call: |
3246 | 3246 | ||
3247 | png_write_flush(png_ptr); | 3247 | png_write_flush(png_ptr); |
3248 | 3248 | ||
3249 | and to have libpng flush the output stream periodically after a certain | 3249 | and to have libpng flush the output stream periodically after a certain |
3250 | number of scanlines have been written, call: | 3250 | number of scanlines have been written, call: |
3251 | 3251 | ||
3252 | png_set_flush(png_ptr, nrows); | 3252 | png_set_flush(png_ptr, nrows); |
3253 | 3253 | ||
3254 | Note that the distance between rows is from the last time png_write_flush() | 3254 | Note that the distance between rows is from the last time png_write_flush() |
3255 | was called, or the first row of the image if it has never been called. | 3255 | was called, or the first row of the image if it has never been called. |
3256 | So if you write 50 lines, and then png_set_flush 25, it will flush the | 3256 | So if you write 50 lines, and then png_set_flush 25, it will flush the |
3257 | output on the next scanline, and every 25 lines thereafter, unless | 3257 | output on the next scanline, and every 25 lines thereafter, unless |
3258 | png_write_flush() is called before 25 more lines have been written. | 3258 | png_write_flush() is called before 25 more lines have been written. |
3259 | If nrows is too small (less than about 10 lines for a 640 pixel wide | 3259 | If nrows is too small (less than about 10 lines for a 640 pixel wide |
3260 | RGB image) the image compression may decrease noticeably (although this | 3260 | RGB image) the image compression may decrease noticeably (although this |
3261 | may be acceptable for real-time applications). Infrequent flushing will | 3261 | may be acceptable for real-time applications). Infrequent flushing will |
3262 | only degrade the compression performance by a few percent over images | 3262 | only degrade the compression performance by a few percent over images |
3263 | that do not use flushing. | 3263 | that do not use flushing. |
3264 | 3264 | ||
3265 | Writing the image data | 3265 | Writing the image data |
3266 | 3266 | ||
3267 | That's it for the transformations. Now you can write the image data. | 3267 | That's it for the transformations. Now you can write the image data. |
3268 | The simplest way to do this is in one function call. If you have the | 3268 | The simplest way to do this is in one function call. If you have the |
3269 | whole image in memory, you can just call png_write_image() and libpng | 3269 | whole image in memory, you can just call png_write_image() and libpng |
3270 | will write the image. You will need to pass in an array of pointers to | 3270 | will write the image. You will need to pass in an array of pointers to |
3271 | each row. This function automatically handles interlacing, so you don't | 3271 | each row. This function automatically handles interlacing, so you don't |
3272 | need to call png_set_interlace_handling() or call this function multiple | 3272 | need to call png_set_interlace_handling() or call this function multiple |
3273 | times, or any of that other stuff necessary with png_write_rows(). | 3273 | times, or any of that other stuff necessary with png_write_rows(). |
3274 | 3274 | ||
3275 | png_write_image(png_ptr, row_pointers); | 3275 | png_write_image(png_ptr, row_pointers); |
3276 | 3276 | ||
3277 | where row_pointers is: | 3277 | where row_pointers is: |
3278 | 3278 | ||
3279 | png_byte *row_pointers[height]; | 3279 | png_byte *row_pointers[height]; |
3280 | 3280 | ||
3281 | You can point to void or char or whatever you use for pixels. | 3281 | You can point to void or char or whatever you use for pixels. |
3282 | 3282 | ||
3283 | If you don't want to write the whole image at once, you can | 3283 | If you don't want to write the whole image at once, you can |
3284 | use png_write_rows() instead. If the file is not interlaced, | 3284 | use png_write_rows() instead. If the file is not interlaced, |
3285 | this is simple: | 3285 | this is simple: |
3286 | 3286 | ||
3287 | png_write_rows(png_ptr, row_pointers, | 3287 | png_write_rows(png_ptr, row_pointers, |
3288 | number_of_rows); | 3288 | number_of_rows); |
3289 | 3289 | ||
3290 | row_pointers is the same as in the png_write_image() call. | 3290 | row_pointers is the same as in the png_write_image() call. |
3291 | 3291 | ||
3292 | If you are just writing one row at a time, you can do this with | 3292 | If you are just writing one row at a time, you can do this with |
3293 | a single row_pointer instead of an array of row_pointers: | 3293 | a single row_pointer instead of an array of row_pointers: |
3294 | 3294 | ||
3295 | png_bytep row_pointer = row; | 3295 | png_bytep row_pointer = row; |
3296 | 3296 | ||
3297 | png_write_row(png_ptr, row_pointer); | 3297 | png_write_row(png_ptr, row_pointer); |
3298 | 3298 | ||
3299 | When the file is interlaced, things can get a good deal more complicated. | 3299 | When the file is interlaced, things can get a good deal more complicated. |
3300 | The only currently (as of the PNG Specification version 1.2, dated July | 3300 | The only currently (as of the PNG Specification version 1.2, dated July |
3301 | 1999) defined interlacing scheme for PNG files is the "Adam7" interlace | 3301 | 1999) defined interlacing scheme for PNG files is the "Adam7" interlace |
3302 | scheme, that breaks down an image into seven smaller images of varying | 3302 | scheme, that breaks down an image into seven smaller images of varying |
3303 | size. libpng will build these images for you, or you can do them | 3303 | size. libpng will build these images for you, or you can do them |
3304 | yourself. If you want to build them yourself, see the PNG specification | 3304 | yourself. If you want to build them yourself, see the PNG specification |
3305 | for details of which pixels to write when. | 3305 | for details of which pixels to write when. |
3306 | 3306 | ||
3307 | If you don't want libpng to handle the interlacing details, just | 3307 | If you don't want libpng to handle the interlacing details, just |
3308 | use png_set_interlace_handling() and call png_write_rows() the | 3308 | use png_set_interlace_handling() and call png_write_rows() the |
3309 | correct number of times to write all the sub-images | 3309 | correct number of times to write all the sub-images |
3310 | (png_set_interlace_handling() returns the number of sub-images.) | 3310 | (png_set_interlace_handling() returns the number of sub-images.) |
3311 | 3311 | ||
3312 | If you want libpng to build the sub-images, call this before you start | 3312 | If you want libpng to build the sub-images, call this before you start |
3313 | writing any rows: | 3313 | writing any rows: |
3314 | 3314 | ||
3315 | number_of_passes = png_set_interlace_handling(png_ptr); | 3315 | number_of_passes = png_set_interlace_handling(png_ptr); |
3316 | 3316 | ||
3317 | This will return the number of passes needed. Currently, this is seven, | 3317 | This will return the number of passes needed. Currently, this is seven, |
3318 | but may change if another interlace type is added. | 3318 | but may change if another interlace type is added. |
3319 | 3319 | ||
3320 | Then write the complete image number_of_passes times. | 3320 | Then write the complete image number_of_passes times. |
3321 | 3321 | ||
3322 | png_write_rows(png_ptr, row_pointers, number_of_rows); | 3322 | png_write_rows(png_ptr, row_pointers, number_of_rows); |
3323 | 3323 | ||
3324 | Think carefully before you write an interlaced image. Typically code that | 3324 | Think carefully before you write an interlaced image. Typically code that |
3325 | reads such images reads all the image data into memory, uncompressed, before | 3325 | reads such images reads all the image data into memory, uncompressed, before |
3326 | doing any processing. Only code that can display an image on the fly can | 3326 | doing any processing. Only code that can display an image on the fly can |
3327 | take advantage of the interlacing and even then the image has to be exactly | 3327 | take advantage of the interlacing and even then the image has to be exactly |
3328 | the correct size for the output device, because scaling an image requires | 3328 | the correct size for the output device, because scaling an image requires |
3329 | adjacent pixels and these are not available until all the passes have been | 3329 | adjacent pixels and these are not available until all the passes have been |
3330 | read. | 3330 | read. |
3331 | 3331 | ||
3332 | If you do write an interlaced image you will hardly ever need to handle | 3332 | If you do write an interlaced image you will hardly ever need to handle |
3333 | the interlacing yourself. Call png_set_interlace_handling() and use the | 3333 | the interlacing yourself. Call png_set_interlace_handling() and use the |
3334 | approach described above. | 3334 | approach described above. |
3335 | 3335 | ||
3336 | The only time it is conceivable that you will really need to write an | 3336 | The only time it is conceivable that you will really need to write an |
3337 | interlaced image pass-by-pass is when you have read one pass by pass and | 3337 | interlaced image pass-by-pass is when you have read one pass by pass and |
3338 | made some pixel-by-pixel transformation to it, as described in the read | 3338 | made some pixel-by-pixel transformation to it, as described in the read |
3339 | code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros | 3339 | code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros |
3340 | to determine the size of each sub-image in turn and simply write the rows | 3340 | to determine the size of each sub-image in turn and simply write the rows |
3341 | you obtained from the read code. | 3341 | you obtained from the read code. |
3342 | 3342 | ||
3343 | Finishing a sequential write | 3343 | Finishing a sequential write |
3344 | 3344 | ||
3345 | After you are finished writing the image, you should finish writing | 3345 | After you are finished writing the image, you should finish writing |
3346 | the file. If you are interested in writing comments or time, you should | 3346 | the file. If you are interested in writing comments or time, you should |
3347 | pass an appropriately filled png_info pointer. If you are not interested, | 3347 | pass an appropriately filled png_info pointer. If you are not interested, |
3348 | you can pass NULL. | 3348 | you can pass NULL. |
3349 | 3349 | ||
3350 | png_write_end(png_ptr, info_ptr); | 3350 | png_write_end(png_ptr, info_ptr); |
3351 | 3351 | ||
3352 | When you are done, you can free all memory used by libpng like this: | 3352 | When you are done, you can free all memory used by libpng like this: |
3353 | 3353 | ||
3354 | png_destroy_write_struct(&png_ptr, &info_ptr); | 3354 | png_destroy_write_struct(&png_ptr, &info_ptr); |
3355 | 3355 | ||
3356 | It is also possible to individually free the info_ptr members that | 3356 | It is also possible to individually free the info_ptr members that |
3357 | point to libpng-allocated storage with the following function: | 3357 | point to libpng-allocated storage with the following function: |
3358 | 3358 | ||
3359 | png_free_data(png_ptr, info_ptr, mask, seq) | 3359 | png_free_data(png_ptr, info_ptr, mask, seq) |
3360 | 3360 | ||
3361 | mask - identifies data to be freed, a mask | 3361 | mask - identifies data to be freed, a mask |
3362 | containing the bitwise OR of one or | 3362 | containing the bitwise OR of one or |
3363 | more of | 3363 | more of |
3364 | PNG_FREE_PLTE, PNG_FREE_TRNS, | 3364 | PNG_FREE_PLTE, PNG_FREE_TRNS, |
3365 | PNG_FREE_HIST, PNG_FREE_ICCP, | 3365 | PNG_FREE_HIST, PNG_FREE_ICCP, |
3366 | PNG_FREE_PCAL, PNG_FREE_ROWS, | 3366 | PNG_FREE_PCAL, PNG_FREE_ROWS, |
3367 | PNG_FREE_SCAL, PNG_FREE_SPLT, | 3367 | PNG_FREE_SCAL, PNG_FREE_SPLT, |
3368 | PNG_FREE_TEXT, PNG_FREE_UNKN, | 3368 | PNG_FREE_TEXT, PNG_FREE_UNKN, |
3369 | or simply PNG_FREE_ALL | 3369 | or simply PNG_FREE_ALL |
3370 | 3370 | ||
3371 | seq - sequence number of item to be freed | 3371 | seq - sequence number of item to be freed |
3372 | (-1 for all items) | 3372 | (-1 for all items) |
3373 | 3373 | ||
3374 | This function may be safely called when the relevant storage has | 3374 | This function may be safely called when the relevant storage has |
3375 | already been freed, or has not yet been allocated, or was allocated | 3375 | already been freed, or has not yet been allocated, or was allocated |
3376 | by the user and not by libpng, and will in those cases do nothing. | 3376 | by the user and not by libpng, and will in those cases do nothing. |
3377 | The "seq" parameter is ignored if only one item of the selected data | 3377 | The "seq" parameter is ignored if only one item of the selected data |
3378 | type, such as PLTE, is allowed. If "seq" is not -1, and multiple items | 3378 | type, such as PLTE, is allowed. If "seq" is not -1, and multiple items |
3379 | are allowed for the data type identified in the mask, such as text or | 3379 | are allowed for the data type identified in the mask, such as text or |
3380 | sPLT, only the n'th item in the structure is freed, where n is "seq". | 3380 | sPLT, only the n'th item in the structure is freed, where n is "seq". |
3381 | 3381 | ||
3382 | If you allocated data such as a palette that you passed in to libpng | 3382 | If you allocated data such as a palette that you passed in to libpng |
3383 | with png_set_*, you must not free it until just before the call to | 3383 | with png_set_*, you must not free it until just before the call to |
3384 | png_destroy_write_struct(). | 3384 | png_destroy_write_struct(). |
3385 | 3385 | ||
3386 | The default behavior is only to free data that was allocated internally | 3386 | The default behavior is only to free data that was allocated internally |
3387 | by libpng. This can be changed, so that libpng will not free the data, | 3387 | by libpng. This can be changed, so that libpng will not free the data, |
3388 | or so that it will free data that was allocated by the user with png_malloc() | 3388 | or so that it will free data that was allocated by the user with png_malloc() |
3389 | or png_zalloc() and passed in via a png_set_*() function, with | 3389 | or png_zalloc() and passed in via a png_set_*() function, with |
3390 | 3390 | ||
3391 | png_data_freer(png_ptr, info_ptr, freer, mask) | 3391 | png_data_freer(png_ptr, info_ptr, freer, mask) |
3392 | 3392 | ||
3393 | freer - one of | 3393 | freer - one of |
3394 | PNG_DESTROY_WILL_FREE_DATA | 3394 | PNG_DESTROY_WILL_FREE_DATA |
3395 | PNG_SET_WILL_FREE_DATA | 3395 | PNG_SET_WILL_FREE_DATA |
3396 | PNG_USER_WILL_FREE_DATA | 3396 | PNG_USER_WILL_FREE_DATA |
3397 | 3397 | ||
3398 | mask - which data elements are affected | 3398 | mask - which data elements are affected |
3399 | same choices as in png_free_data() | 3399 | same choices as in png_free_data() |
3400 | 3400 | ||
3401 | For example, to transfer responsibility for some data from a read structure | 3401 | For example, to transfer responsibility for some data from a read structure |
3402 | to a write structure, you could use | 3402 | to a write structure, you could use |
3403 | 3403 | ||
3404 | png_data_freer(read_ptr, read_info_ptr, | 3404 | png_data_freer(read_ptr, read_info_ptr, |
3405 | PNG_USER_WILL_FREE_DATA, | 3405 | PNG_USER_WILL_FREE_DATA, |
3406 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) | 3406 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) |
3407 | 3407 | ||
3408 | png_data_freer(write_ptr, write_info_ptr, | 3408 | png_data_freer(write_ptr, write_info_ptr, |
3409 | PNG_DESTROY_WILL_FREE_DATA, | 3409 | PNG_DESTROY_WILL_FREE_DATA, |
3410 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) | 3410 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST) |
3411 | 3411 | ||
3412 | thereby briefly reassigning responsibility for freeing to the user but | 3412 | thereby briefly reassigning responsibility for freeing to the user but |
3413 | immediately afterwards reassigning it once more to the write_destroy | 3413 | immediately afterwards reassigning it once more to the write_destroy |
3414 | function. Having done this, it would then be safe to destroy the read | 3414 | function. Having done this, it would then be safe to destroy the read |
3415 | structure and continue to use the PLTE, tRNS, and hIST data in the write | 3415 | structure and continue to use the PLTE, tRNS, and hIST data in the write |
3416 | structure. | 3416 | structure. |
3417 | 3417 | ||
3418 | This function only affects data that has already been allocated. | 3418 | This function only affects data that has already been allocated. |
3419 | You can call this function before calling after the png_set_*() functions | 3419 | You can call this function before calling after the png_set_*() functions |
3420 | to control whether the user or png_destroy_*() is supposed to free the data. | 3420 | to control whether the user or png_destroy_*() is supposed to free the data. |
3421 | When the user assumes responsibility for libpng-allocated data, the | 3421 | When the user assumes responsibility for libpng-allocated data, the |
3422 | application must use | 3422 | application must use |
3423 | png_free() to free it, and when the user transfers responsibility to libpng | 3423 | png_free() to free it, and when the user transfers responsibility to libpng |
3424 | for data that the user has allocated, the user must have used png_malloc() | 3424 | for data that the user has allocated, the user must have used png_malloc() |
3425 | or png_zalloc() to allocate it. | 3425 | or png_zalloc() to allocate it. |
3426 | 3426 | ||
3427 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword | 3427 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword |
3428 | separately, do not transfer responsibility for freeing text_ptr to libpng, | 3428 | separately, do not transfer responsibility for freeing text_ptr to libpng, |
3429 | because when libpng fills a png_text structure it combines these members with | 3429 | because when libpng fills a png_text structure it combines these members with |
3430 | the key member, and png_free_data() will free only text_ptr.key. Similarly, | 3430 | the key member, and png_free_data() will free only text_ptr.key. Similarly, |
3431 | if you transfer responsibility for free'ing text_ptr from libpng to your | 3431 | if you transfer responsibility for free'ing text_ptr from libpng to your |
3432 | application, your application must not separately free those members. | 3432 | application, your application must not separately free those members. |
3433 | For a more compact example of writing a PNG image, see the file example.c. | 3433 | For a more compact example of writing a PNG image, see the file example.c. |
3434 | 3434 | ||
3435 | V. Modifying/Customizing libpng: | 3435 | V. Modifying/Customizing libpng: |
3436 | 3436 | ||
3437 | There are two issues here. The first is changing how libpng does | 3437 | There are two issues here. The first is changing how libpng does |
3438 | standard things like memory allocation, input/output, and error handling. | 3438 | standard things like memory allocation, input/output, and error handling. |
3439 | The second deals with more complicated things like adding new chunks, | 3439 | The second deals with more complicated things like adding new chunks, |
3440 | adding new transformations, and generally changing how libpng works. | 3440 | adding new transformations, and generally changing how libpng works. |
3441 | Both of those are compile-time issues; that is, they are generally | 3441 | Both of those are compile-time issues; that is, they are generally |
3442 | determined at the time the code is written, and there is rarely a need | 3442 | determined at the time the code is written, and there is rarely a need |
3443 | to provide the user with a means of changing them. | 3443 | to provide the user with a means of changing them. |
3444 | 3444 | ||
3445 | Memory allocation, input/output, and error handling | 3445 | Memory allocation, input/output, and error handling |
3446 | 3446 | ||
3447 | All of the memory allocation, input/output, and error handling in libpng | 3447 | All of the memory allocation, input/output, and error handling in libpng |
3448 | goes through callbacks that are user-settable. The default routines are | 3448 | goes through callbacks that are user-settable. The default routines are |
3449 | in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change | 3449 | in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change |
3450 | these functions, call the appropriate png_set_*_fn() function. | 3450 | these functions, call the appropriate png_set_*_fn() function. |
3451 | 3451 | ||
3452 | Memory allocation is done through the functions png_malloc(), png_calloc(), | 3452 | Memory allocation is done through the functions png_malloc(), png_calloc(), |
3453 | and png_free(). These currently just call the standard C functions. | 3453 | and png_free(). These currently just call the standard C functions. |
3454 | png_calloc() calls png_malloc() and then clears the newly | 3454 | png_calloc() calls png_malloc() and then clears the newly |
3455 | allocated memory to zero. There is limited support for certain systems | 3455 | allocated memory to zero. There is limited support for certain systems |
3456 | with segmented memory architectures and the types of pointers declared by | 3456 | with segmented memory architectures and the types of pointers declared by |
3457 | png.h match this; you will have to use appropriate pointers in your | 3457 | png.h match this; you will have to use appropriate pointers in your |
3458 | application. Since it is | 3458 | application. Since it is |
3459 | unlikely that the method of handling memory allocation on a platform | 3459 | unlikely that the method of handling memory allocation on a platform |
3460 | will change between applications, these functions must be modified in | 3460 | will change between applications, these functions must be modified in |
3461 | the library at compile time. If you prefer to use a different method | 3461 | the library at compile time. If you prefer to use a different method |
3462 | of allocating and freeing data, you can use png_create_read_struct_2() or | 3462 | of allocating and freeing data, you can use png_create_read_struct_2() or |
3463 | png_create_write_struct_2() to register your own functions as described | 3463 | png_create_write_struct_2() to register your own functions as described |
3464 | above. These functions also provide a void pointer that can be retrieved | 3464 | above. These functions also provide a void pointer that can be retrieved |
3465 | via | 3465 | via |
3466 | 3466 | ||
3467 | mem_ptr=png_get_mem_ptr(png_ptr); | 3467 | mem_ptr=png_get_mem_ptr(png_ptr); |
3468 | 3468 | ||
3469 | Your replacement memory functions must have prototypes as follows: | 3469 | Your replacement memory functions must have prototypes as follows: |
3470 | 3470 | ||
3471 | png_voidp malloc_fn(png_structp png_ptr, | 3471 | png_voidp malloc_fn(png_structp png_ptr, |
3472 | png_alloc_size_t size); | 3472 | png_alloc_size_t size); |
3473 | 3473 | ||
3474 | void free_fn(png_structp png_ptr, png_voidp ptr); | 3474 | void free_fn(png_structp png_ptr, png_voidp ptr); |
3475 | 3475 | ||
3476 | Your malloc_fn() must return NULL in case of failure. The png_malloc() | 3476 | Your malloc_fn() must return NULL in case of failure. The png_malloc() |
3477 | function will normally call png_error() if it receives a NULL from the | 3477 | function will normally call png_error() if it receives a NULL from the |
3478 | system memory allocator or from your replacement malloc_fn(). | 3478 | system memory allocator or from your replacement malloc_fn(). |
3479 | 3479 | ||
3480 | Your free_fn() will never be called with a NULL ptr, since libpng's | 3480 | Your free_fn() will never be called with a NULL ptr, since libpng's |
3481 | png_free() checks for NULL before calling free_fn(). | 3481 | png_free() checks for NULL before calling free_fn(). |
3482 | 3482 | ||
3483 | Input/Output in libpng is done through png_read() and png_write(), | 3483 | Input/Output in libpng is done through png_read() and png_write(), |
3484 | which currently just call fread() and fwrite(). The FILE * is stored in | 3484 | which currently just call fread() and fwrite(). The FILE * is stored in |
3485 | png_struct and is initialized via png_init_io(). If you wish to change | 3485 | png_struct and is initialized via png_init_io(). If you wish to change |
3486 | the method of I/O, the library supplies callbacks that you can set | 3486 | the method of I/O, the library supplies callbacks that you can set |
3487 | through the function png_set_read_fn() and png_set_write_fn() at run | 3487 | through the function png_set_read_fn() and png_set_write_fn() at run |
3488 | time, instead of calling the png_init_io() function. These functions | 3488 | time, instead of calling the png_init_io() function. These functions |
3489 | also provide a void pointer that can be retrieved via the function | 3489 | also provide a void pointer that can be retrieved via the function |
3490 | png_get_io_ptr(). For example: | 3490 | png_get_io_ptr(). For example: |
3491 | 3491 | ||
3492 | png_set_read_fn(png_structp read_ptr, | 3492 | png_set_read_fn(png_structp read_ptr, |
3493 | voidp read_io_ptr, png_rw_ptr read_data_fn) | 3493 | voidp read_io_ptr, png_rw_ptr read_data_fn) |
3494 | 3494 | ||
3495 | png_set_write_fn(png_structp write_ptr, | 3495 | png_set_write_fn(png_structp write_ptr, |
3496 | voidp write_io_ptr, png_rw_ptr write_data_fn, | 3496 | voidp write_io_ptr, png_rw_ptr write_data_fn, |
3497 | png_flush_ptr output_flush_fn); | 3497 | png_flush_ptr output_flush_fn); |
3498 | 3498 | ||
3499 | voidp read_io_ptr = png_get_io_ptr(read_ptr); | 3499 | voidp read_io_ptr = png_get_io_ptr(read_ptr); |
3500 | voidp write_io_ptr = png_get_io_ptr(write_ptr); | 3500 | voidp write_io_ptr = png_get_io_ptr(write_ptr); |
3501 | 3501 | ||
3502 | The replacement I/O functions must have prototypes as follows: | 3502 | The replacement I/O functions must have prototypes as follows: |
3503 | 3503 | ||
3504 | void user_read_data(png_structp png_ptr, | 3504 | void user_read_data(png_structp png_ptr, |
3505 | png_bytep data, png_size_t length); | 3505 | png_bytep data, png_size_t length); |
3506 | 3506 | ||
3507 | void user_write_data(png_structp png_ptr, | 3507 | void user_write_data(png_structp png_ptr, |
3508 | png_bytep data, png_size_t length); | 3508 | png_bytep data, png_size_t length); |
3509 | 3509 | ||
3510 | void user_flush_data(png_structp png_ptr); | 3510 | void user_flush_data(png_structp png_ptr); |
3511 | 3511 | ||
3512 | The user_read_data() function is responsible for detecting and | 3512 | The user_read_data() function is responsible for detecting and |
3513 | handling end-of-data errors. | 3513 | handling end-of-data errors. |
3514 | 3514 | ||
3515 | Supplying NULL for the read, write, or flush functions sets them back | 3515 | Supplying NULL for the read, write, or flush functions sets them back |
3516 | to using the default C stream functions, which expect the io_ptr to | 3516 | to using the default C stream functions, which expect the io_ptr to |
3517 | point to a standard *FILE structure. It is probably a mistake | 3517 | point to a standard *FILE structure. It is probably a mistake |
3518 | to use NULL for one of write_data_fn and output_flush_fn but not both | 3518 | to use NULL for one of write_data_fn and output_flush_fn but not both |
3519 | of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined. | 3519 | of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined. |
3520 | It is an error to read from a write stream, and vice versa. | 3520 | It is an error to read from a write stream, and vice versa. |
3521 | 3521 | ||
3522 | Error handling in libpng is done through png_error() and png_warning(). | 3522 | Error handling in libpng is done through png_error() and png_warning(). |
3523 | Errors handled through png_error() are fatal, meaning that png_error() | 3523 | Errors handled through png_error() are fatal, meaning that png_error() |
3524 | should never return to its caller. Currently, this is handled via | 3524 | should never return to its caller. Currently, this is handled via |
3525 | setjmp() and longjmp() (unless you have compiled libpng with | 3525 | setjmp() and longjmp() (unless you have compiled libpng with |
3526 | PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()), | 3526 | PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()), |
3527 | but you could change this to do things like exit() if you should wish, | 3527 | but you could change this to do things like exit() if you should wish, |
3528 | as long as your function does not return. | 3528 | as long as your function does not return. |
3529 | 3529 | ||
3530 | On non-fatal errors, png_warning() is called | 3530 | On non-fatal errors, png_warning() is called |
3531 | to print a warning message, and then control returns to the calling code. | 3531 | to print a warning message, and then control returns to the calling code. |
3532 | By default png_error() and png_warning() print a message on stderr via | 3532 | By default png_error() and png_warning() print a message on stderr via |
3533 | fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined | 3533 | fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined |
3534 | (because you don't want the messages) or PNG_NO_STDIO defined (because | 3534 | (because you don't want the messages) or PNG_NO_STDIO defined (because |
3535 | fprintf() isn't available). If you wish to change the behavior of the error | 3535 | fprintf() isn't available). If you wish to change the behavior of the error |
3536 | functions, you will need to set up your own message callbacks. These | 3536 | functions, you will need to set up your own message callbacks. These |
3537 | functions are normally supplied at the time that the png_struct is created. | 3537 | functions are normally supplied at the time that the png_struct is created. |
3538 | It is also possible to redirect errors and warnings to your own replacement | 3538 | It is also possible to redirect errors and warnings to your own replacement |
3539 | functions after png_create_*_struct() has been called by calling: | 3539 | functions after png_create_*_struct() has been called by calling: |
3540 | 3540 | ||
3541 | png_set_error_fn(png_structp png_ptr, | 3541 | png_set_error_fn(png_structp png_ptr, |
3542 | png_voidp error_ptr, png_error_ptr error_fn, | 3542 | png_voidp error_ptr, png_error_ptr error_fn, |
3543 | png_error_ptr warning_fn); | 3543 | png_error_ptr warning_fn); |
3544 | 3544 | ||
3545 | png_voidp error_ptr = png_get_error_ptr(png_ptr); | 3545 | png_voidp error_ptr = png_get_error_ptr(png_ptr); |
3546 | 3546 | ||
3547 | If NULL is supplied for either error_fn or warning_fn, then the libpng | 3547 | If NULL is supplied for either error_fn or warning_fn, then the libpng |
3548 | default function will be used, calling fprintf() and/or longjmp() if a | 3548 | default function will be used, calling fprintf() and/or longjmp() if a |
3549 | problem is encountered. The replacement error functions should have | 3549 | problem is encountered. The replacement error functions should have |
3550 | parameters as follows: | 3550 | parameters as follows: |
3551 | 3551 | ||
3552 | void user_error_fn(png_structp png_ptr, | 3552 | void user_error_fn(png_structp png_ptr, |
3553 | png_const_charp error_msg); | 3553 | png_const_charp error_msg); |
3554 | 3554 | ||
3555 | void user_warning_fn(png_structp png_ptr, | 3555 | void user_warning_fn(png_structp png_ptr, |
3556 | png_const_charp warning_msg); | 3556 | png_const_charp warning_msg); |
3557 | 3557 | ||
3558 | The motivation behind using setjmp() and longjmp() is the C++ throw and | 3558 | The motivation behind using setjmp() and longjmp() is the C++ throw and |
3559 | catch exception handling methods. This makes the code much easier to write, | 3559 | catch exception handling methods. This makes the code much easier to write, |
3560 | as there is no need to check every return code of every function call. | 3560 | as there is no need to check every return code of every function call. |
3561 | However, there are some uncertainties about the status of local variables | 3561 | However, there are some uncertainties about the status of local variables |
3562 | after a longjmp, so the user may want to be careful about doing anything | 3562 | after a longjmp, so the user may want to be careful about doing anything |
3563 | after setjmp returns non-zero besides returning itself. Consult your | 3563 | after setjmp returns non-zero besides returning itself. Consult your |
3564 | compiler documentation for more details. For an alternative approach, you | 3564 | compiler documentation for more details. For an alternative approach, you |
3565 | may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net), | 3565 | may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net), |
3566 | which is illustrated in pngvalid.c and in contrib/visupng. | 3566 | which is illustrated in pngvalid.c and in contrib/visupng. |
3567 | 3567 | ||
3568 | Custom chunks | 3568 | Custom chunks |
3569 | 3569 | ||
3570 | If you need to read or write custom chunks, you may need to get deeper | 3570 | If you need to read or write custom chunks, you may need to get deeper |
3571 | into the libpng code. The library now has mechanisms for storing | 3571 | into the libpng code. The library now has mechanisms for storing |
3572 | and writing chunks of unknown type; you can even declare callbacks | 3572 | and writing chunks of unknown type; you can even declare callbacks |
3573 | for custom chunks. However, this may not be good enough if the | 3573 | for custom chunks. However, this may not be good enough if the |
3574 | library code itself needs to know about interactions between your | 3574 | library code itself needs to know about interactions between your |
3575 | chunk and existing `intrinsic' chunks. | 3575 | chunk and existing `intrinsic' chunks. |
3576 | 3576 | ||
3577 | If you need to write a new intrinsic chunk, first read the PNG | 3577 | If you need to write a new intrinsic chunk, first read the PNG |
3578 | specification. Acquire a first level of understanding of how it works. | 3578 | specification. Acquire a first level of understanding of how it works. |
3579 | Pay particular attention to the sections that describe chunk names, | 3579 | Pay particular attention to the sections that describe chunk names, |
3580 | and look at how other chunks were designed, so you can do things | 3580 | and look at how other chunks were designed, so you can do things |
3581 | similarly. Second, check out the sections of libpng that read and | 3581 | similarly. Second, check out the sections of libpng that read and |
3582 | write chunks. Try to find a chunk that is similar to yours and use | 3582 | write chunks. Try to find a chunk that is similar to yours and use |
3583 | it as a template. More details can be found in the comments inside | 3583 | it as a template. More details can be found in the comments inside |
3584 | the code. It is best to handle private or unknown chunks in a generic method, | 3584 | the code. It is best to handle private or unknown chunks in a generic method, |
3585 | via callback functions, instead of by modifying libpng functions. This | 3585 | via callback functions, instead of by modifying libpng functions. This |
3586 | is illustrated in pngtest.c, which uses a callback function to handle a | 3586 | is illustrated in pngtest.c, which uses a callback function to handle a |
3587 | private "vpAg" chunk and the new "sTER" chunk, which are both unknown to | 3587 | private "vpAg" chunk and the new "sTER" chunk, which are both unknown to |
3588 | libpng. | 3588 | libpng. |
3589 | 3589 | ||
3590 | If you wish to write your own transformation for the data, look through | 3590 | If you wish to write your own transformation for the data, look through |
3591 | the part of the code that does the transformations, and check out some of | 3591 | the part of the code that does the transformations, and check out some of |
3592 | the simpler ones to get an idea of how they work. Try to find a similar | 3592 | the simpler ones to get an idea of how they work. Try to find a similar |
3593 | transformation to the one you want to add and copy off of it. More details | 3593 | transformation to the one you want to add and copy off of it. More details |
3594 | can be found in the comments inside the code itself. | 3594 | can be found in the comments inside the code itself. |
3595 | 3595 | ||
3596 | Configuring for 16-bit platforms | 3596 | Configuring for 16-bit platforms |
3597 | 3597 | ||
3598 | You will want to look into zconf.h to tell zlib (and thus libpng) that | 3598 | You will want to look into zconf.h to tell zlib (and thus libpng) that |
3599 | it cannot allocate more then 64K at a time. Even if you can, the memory | 3599 | it cannot allocate more then 64K at a time. Even if you can, the memory |
3600 | won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K. | 3600 | won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K. |
3601 | 3601 | ||
3602 | Configuring for DOS | 3602 | Configuring for DOS |
3603 | 3603 | ||
3604 | For DOS users who only have access to the lower 640K, you will | 3604 | For DOS users who only have access to the lower 640K, you will |
3605 | have to limit zlib's memory usage via a png_set_compression_mem_level() | 3605 | have to limit zlib's memory usage via a png_set_compression_mem_level() |
3606 | call. See zlib.h or zconf.h in the zlib library for more information. | 3606 | call. See zlib.h or zconf.h in the zlib library for more information. |
3607 | 3607 | ||
3608 | Configuring for Medium Model | 3608 | Configuring for Medium Model |
3609 | 3609 | ||
3610 | Libpng's support for medium model has been tested on most of the popular | 3610 | Libpng's support for medium model has been tested on most of the popular |
3611 | compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets | 3611 | compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets |
3612 | defined, and FAR gets defined to far in pngconf.h, and you should be | 3612 | defined, and FAR gets defined to far in pngconf.h, and you should be |
3613 | all set. Everything in the library (except for zlib's structure) is | 3613 | all set. Everything in the library (except for zlib's structure) is |
3614 | expecting far data. You must use the typedefs with the p or pp on | 3614 | expecting far data. You must use the typedefs with the p or pp on |
3615 | the end for pointers (or at least look at them and be careful). Make | 3615 | the end for pointers (or at least look at them and be careful). Make |
3616 | note that the rows of data are defined as png_bytepp, which is | 3616 | note that the rows of data are defined as png_bytepp, which is |
3617 | an "unsigned char far * far *". | 3617 | an "unsigned char far * far *". |
3618 | 3618 | ||
3619 | Configuring for gui/windowing platforms: | 3619 | Configuring for gui/windowing platforms: |
3620 | 3620 | ||
3621 | You will need to write new error and warning functions that use the GUI | 3621 | You will need to write new error and warning functions that use the GUI |
3622 | interface, as described previously, and set them to be the error and | 3622 | interface, as described previously, and set them to be the error and |
3623 | warning functions at the time that png_create_*_struct() is called, | 3623 | warning functions at the time that png_create_*_struct() is called, |
3624 | in order to have them available during the structure initialization. | 3624 | in order to have them available during the structure initialization. |
3625 | They can be changed later via png_set_error_fn(). On some compilers, | 3625 | They can be changed later via png_set_error_fn(). On some compilers, |
3626 | you may also have to change the memory allocators (png_malloc, etc.). | 3626 | you may also have to change the memory allocators (png_malloc, etc.). |
3627 | 3627 | ||
3628 | Configuring for compiler xxx: | 3628 | Configuring for compiler xxx: |
3629 | 3629 | ||
3630 | All includes for libpng are in pngconf.h. If you need to add, change | 3630 | All includes for libpng are in pngconf.h. If you need to add, change |
3631 | or delete an include, this is the place to do it. | 3631 | or delete an include, this is the place to do it. |
3632 | The includes that are not needed outside libpng are placed in pngpriv.h, | 3632 | The includes that are not needed outside libpng are placed in pngpriv.h, |
3633 | which is only used by the routines inside libpng itself. | 3633 | which is only used by the routines inside libpng itself. |
3634 | The files in libpng proper only include pngpriv.h and png.h, which | 3634 | The files in libpng proper only include pngpriv.h and png.h, which |
3635 | in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h. | 3635 | in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h. |
3636 | As of libpng-1.5.0, pngpriv.h also includes three other private header | 3636 | As of libpng-1.5.0, pngpriv.h also includes three other private header |
3637 | files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material | 3637 | files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material |
3638 | that previously appeared in the public headers. | 3638 | that previously appeared in the public headers. |
3639 | 3639 | ||
3640 | Configuring zlib: | 3640 | Configuring zlib: |
3641 | 3641 | ||
3642 | There are special functions to configure the compression. Perhaps the | 3642 | There are special functions to configure the compression. Perhaps the |
3643 | most useful one changes the compression level, which currently uses | 3643 | most useful one changes the compression level, which currently uses |
3644 | input compression values in the range 0 - 9. The library normally | 3644 | input compression values in the range 0 - 9. The library normally |
3645 | uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests | 3645 | uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests |
3646 | have shown that for a large majority of images, compression values in | 3646 | have shown that for a large majority of images, compression values in |
3647 | the range 3-6 compress nearly as well as higher levels, and do so much | 3647 | the range 3-6 compress nearly as well as higher levels, and do so much |
3648 | faster. For online applications it may be desirable to have maximum speed | 3648 | faster. For online applications it may be desirable to have maximum speed |
3649 | (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also | 3649 | (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also |
3650 | specify no compression (Z_NO_COMPRESSION = 0), but this would create | 3650 | specify no compression (Z_NO_COMPRESSION = 0), but this would create |
3651 | files larger than just storing the raw bitmap. You can specify the | 3651 | files larger than just storing the raw bitmap. You can specify the |
3652 | compression level by calling: | 3652 | compression level by calling: |
3653 | 3653 | ||
3654 | #include zlib.h | 3654 | #include zlib.h |
3655 | png_set_compression_level(png_ptr, level); | 3655 | png_set_compression_level(png_ptr, level); |
3656 | 3656 | ||
3657 | Another useful one is to reduce the memory level used by the library. | 3657 | Another useful one is to reduce the memory level used by the library. |
3658 | The memory level defaults to 8, but it can be lowered if you are | 3658 | The memory level defaults to 8, but it can be lowered if you are |
3659 | short on memory (running DOS, for example, where you only have 640K). | 3659 | short on memory (running DOS, for example, where you only have 640K). |
3660 | Note that the memory level does have an effect on compression; among | 3660 | Note that the memory level does have an effect on compression; among |
3661 | other things, lower levels will result in sections of incompressible | 3661 | other things, lower levels will result in sections of incompressible |
3662 | data being emitted in smaller stored blocks, with a correspondingly | 3662 | data being emitted in smaller stored blocks, with a correspondingly |
3663 | larger relative overhead of up to 15% in the worst case. | 3663 | larger relative overhead of up to 15% in the worst case. |
3664 | 3664 | ||
3665 | #include zlib.h | 3665 | #include zlib.h |
3666 | png_set_compression_mem_level(png_ptr, level); | 3666 | png_set_compression_mem_level(png_ptr, level); |
3667 | 3667 | ||
3668 | The other functions are for configuring zlib. They are not recommended | 3668 | The other functions are for configuring zlib. They are not recommended |
3669 | for normal use and may result in writing an invalid PNG file. See | 3669 | for normal use and may result in writing an invalid PNG file. See |
3670 | zlib.h for more information on what these mean. | 3670 | zlib.h for more information on what these mean. |
3671 | 3671 | ||
3672 | #include zlib.h | 3672 | #include zlib.h |
3673 | png_set_compression_strategy(png_ptr, | 3673 | png_set_compression_strategy(png_ptr, |
3674 | strategy); | 3674 | strategy); |
3675 | 3675 | ||
3676 | png_set_compression_window_bits(png_ptr, | 3676 | png_set_compression_window_bits(png_ptr, |
3677 | window_bits); | 3677 | window_bits); |
3678 | 3678 | ||
3679 | png_set_compression_method(png_ptr, method); | 3679 | png_set_compression_method(png_ptr, method); |
3680 | 3680 | ||
3681 | png_set_compression_buffer_size(png_ptr, size); | 3681 | png_set_compression_buffer_size(png_ptr, size); |
3682 | 3682 | ||
3683 | As of libpng version 1.5.4, additional APIs became | 3683 | As of libpng version 1.5.4, additional APIs became |
3684 | available to set these separately for non-IDAT | 3684 | available to set these separately for non-IDAT |
3685 | compressed chunks such as zTXt, iTXt, and iCCP: | 3685 | compressed chunks such as zTXt, iTXt, and iCCP: |
3686 | 3686 | ||
3687 | #include zlib.h | 3687 | #include zlib.h |
3688 | #if PNG_LIBPNG_VER <= 10504 | 3688 | #if PNG_LIBPNG_VER <= 10504 |
3689 | png_set_text_compression_level(png_ptr, level); | 3689 | png_set_text_compression_level(png_ptr, level); |
3690 | 3690 | ||
3691 | png_set_text_compression_mem_level(png_ptr, level); | 3691 | png_set_text_compression_mem_level(png_ptr, level); |
3692 | 3692 | ||
3693 | png_set_text_compression_strategy(png_ptr, | 3693 | png_set_text_compression_strategy(png_ptr, |
3694 | strategy); | 3694 | strategy); |
3695 | 3695 | ||
3696 | png_set_text_compression_window_bits(png_ptr, | 3696 | png_set_text_compression_window_bits(png_ptr, |
3697 | window_bits); | 3697 | window_bits); |
3698 | 3698 | ||
3699 | png_set_text_compression_method(png_ptr, method); | 3699 | png_set_text_compression_method(png_ptr, method); |
3700 | #endif | 3700 | #endif |
3701 | 3701 | ||
3702 | Controlling row filtering | 3702 | Controlling row filtering |
3703 | 3703 | ||
3704 | If you want to control whether libpng uses filtering or not, which | 3704 | If you want to control whether libpng uses filtering or not, which |
3705 | filters are used, and how it goes about picking row filters, you | 3705 | filters are used, and how it goes about picking row filters, you |
3706 | can call one of these functions. The selection and configuration | 3706 | can call one of these functions. The selection and configuration |
3707 | of row filters can have a significant impact on the size and | 3707 | of row filters can have a significant impact on the size and |
3708 | encoding speed and a somewhat lesser impact on the decoding speed | 3708 | encoding speed and a somewhat lesser impact on the decoding speed |
3709 | of an image. Filtering is enabled by default for RGB and grayscale | 3709 | of an image. Filtering is enabled by default for RGB and grayscale |
3710 | images (with and without alpha), but not for paletted images nor | 3710 | images (with and without alpha), but not for paletted images nor |
3711 | for any images with bit depths less than 8 bits/pixel. | 3711 | for any images with bit depths less than 8 bits/pixel. |
3712 | 3712 | ||
3713 | The 'method' parameter sets the main filtering method, which is | 3713 | The 'method' parameter sets the main filtering method, which is |
3714 | currently only '0' in the PNG 1.2 specification. The 'filters' | 3714 | currently only '0' in the PNG 1.2 specification. The 'filters' |
3715 | parameter sets which filter(s), if any, should be used for each | 3715 | parameter sets which filter(s), if any, should be used for each |
3716 | scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS | 3716 | scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS |
3717 | to turn filtering on and off, respectively. | 3717 | to turn filtering on and off, respectively. |
3718 | 3718 | ||
3719 | Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB, | 3719 | Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB, |
3720 | PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise | 3720 | PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise |
3721 | ORed together with '|' to specify one or more filters to use. | 3721 | ORed together with '|' to specify one or more filters to use. |
3722 | These filters are described in more detail in the PNG specification. | 3722 | These filters are described in more detail in the PNG specification. |
3723 | If you intend to change the filter type during the course of writing | 3723 | If you intend to change the filter type during the course of writing |
3724 | the image, you should start with flags set for all of the filters | 3724 | the image, you should start with flags set for all of the filters |
3725 | you intend to use so that libpng can initialize its internal | 3725 | you intend to use so that libpng can initialize its internal |
3726 | structures appropriately for all of the filter types. (Note that this | 3726 | structures appropriately for all of the filter types. (Note that this |
3727 | means the first row must always be adaptively filtered, because libpng | 3727 | means the first row must always be adaptively filtered, because libpng |
3728 | currently does not allocate the filter buffers until png_write_row() | 3728 | currently does not allocate the filter buffers until png_write_row() |
3729 | is called for the first time.) | 3729 | is called for the first time.) |
3730 | 3730 | ||
3731 | filters = PNG_FILTER_NONE | PNG_FILTER_SUB | 3731 | filters = PNG_FILTER_NONE | PNG_FILTER_SUB |
3732 | PNG_FILTER_UP | PNG_FILTER_AVG | | 3732 | PNG_FILTER_UP | PNG_FILTER_AVG | |
3733 | PNG_FILTER_PAETH | PNG_ALL_FILTERS; | 3733 | PNG_FILTER_PAETH | PNG_ALL_FILTERS; |
3734 | 3734 | ||
3735 | png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, | 3735 | png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, |
3736 | filters); | 3736 | filters); |
3737 | The second parameter can also be | 3737 | The second parameter can also be |
3738 | PNG_INTRAPIXEL_DIFFERENCING if you are | 3738 | PNG_INTRAPIXEL_DIFFERENCING if you are |
3739 | writing a PNG to be embedded in a MNG | 3739 | writing a PNG to be embedded in a MNG |
3740 | datastream. This parameter must be the | 3740 | datastream. This parameter must be the |
3741 | same as the value of filter_method used | 3741 | same as the value of filter_method used |
3742 | in png_set_IHDR(). | 3742 | in png_set_IHDR(). |
3743 | 3743 | ||
3744 | It is also possible to influence how libpng chooses from among the | 3744 | It is also possible to influence how libpng chooses from among the |
3745 | available filters. This is done in one or both of two ways - by | 3745 | available filters. This is done in one or both of two ways - by |
3746 | telling it how important it is to keep the same filter for successive | 3746 | telling it how important it is to keep the same filter for successive |
3747 | rows, and by telling it the relative computational costs of the filters. | 3747 | rows, and by telling it the relative computational costs of the filters. |
3748 | 3748 | ||
3749 | double weights[3] = {1.5, 1.3, 1.1}, | 3749 | double weights[3] = {1.5, 1.3, 1.1}, |
3750 | costs[PNG_FILTER_VALUE_LAST] = | 3750 | costs[PNG_FILTER_VALUE_LAST] = |
3751 | {1.0, 1.3, 1.3, 1.5, 1.7}; | 3751 | {1.0, 1.3, 1.3, 1.5, 1.7}; |
3752 | 3752 | ||
3753 | png_set_filter_heuristics(png_ptr, | 3753 | png_set_filter_heuristics(png_ptr, |
3754 | PNG_FILTER_HEURISTIC_WEIGHTED, 3, | 3754 | PNG_FILTER_HEURISTIC_WEIGHTED, 3, |
3755 | weights, costs); | 3755 | weights, costs); |
3756 | 3756 | ||
3757 | The weights are multiplying factors that indicate to libpng that the | 3757 | The weights are multiplying factors that indicate to libpng that the |
3758 | row filter should be the same for successive rows unless another row filter | 3758 | row filter should be the same for successive rows unless another row filter |
3759 | is that many times better than the previous filter. In the above example, | 3759 | is that many times better than the previous filter. In the above example, |
3760 | if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a | 3760 | if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a |
3761 | "sum of absolute differences" 1.5 x 1.3 times higher than other filters | 3761 | "sum of absolute differences" 1.5 x 1.3 times higher than other filters |
3762 | and still be chosen, while the NONE filter could have a sum 1.1 times | 3762 | and still be chosen, while the NONE filter could have a sum 1.1 times |
3763 | higher than other filters and still be chosen. Unspecified weights are | 3763 | higher than other filters and still be chosen. Unspecified weights are |
3764 | taken to be 1.0, and the specified weights should probably be declining | 3764 | taken to be 1.0, and the specified weights should probably be declining |
3765 | like those above in order to emphasize recent filters over older filters. | 3765 | like those above in order to emphasize recent filters over older filters. |
3766 | 3766 | ||
3767 | The filter costs specify for each filter type a relative decoding cost | 3767 | The filter costs specify for each filter type a relative decoding cost |
3768 | to be considered when selecting row filters. This means that filters | 3768 | to be considered when selecting row filters. This means that filters |
3769 | with higher costs are less likely to be chosen over filters with lower | 3769 | with higher costs are less likely to be chosen over filters with lower |
3770 | costs, unless their "sum of absolute differences" is that much smaller. | 3770 | costs, unless their "sum of absolute differences" is that much smaller. |
3771 | The costs do not necessarily reflect the exact computational speeds of | 3771 | The costs do not necessarily reflect the exact computational speeds of |
3772 | the various filters, since this would unduly influence the final image | 3772 | the various filters, since this would unduly influence the final image |
3773 | size. | 3773 | size. |
3774 | 3774 | ||
3775 | Note that the numbers above were invented purely for this example and | 3775 | Note that the numbers above were invented purely for this example and |
3776 | are given only to help explain the function usage. Little testing has | 3776 | are given only to help explain the function usage. Little testing has |
3777 | been done to find optimum values for either the costs or the weights. | 3777 | been done to find optimum values for either the costs or the weights. |
3778 | 3778 | ||
3779 | Removing unwanted object code | 3779 | Removing unwanted object code |
3780 | 3780 | ||
3781 | There are a bunch of #define's in pngconf.h that control what parts of | 3781 | There are a bunch of #define's in pngconf.h that control what parts of |
3782 | libpng are compiled. All the defines end in _SUPPORTED. If you are | 3782 | libpng are compiled. All the defines end in _SUPPORTED. If you are |
3783 | never going to use a capability, you can change the #define to #undef | 3783 | never going to use a capability, you can change the #define to #undef |
3784 | before recompiling libpng and save yourself code and data space, or | 3784 | before recompiling libpng and save yourself code and data space, or |
3785 | you can turn off individual capabilities with defines that begin with | 3785 | you can turn off individual capabilities with defines that begin with |
3786 | PNG_NO_. | 3786 | PNG_NO_. |
3787 | 3787 | ||
3788 | In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead. | 3788 | In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead. |
3789 | 3789 | ||
3790 | You can also turn all of the transforms and ancillary chunk capabilities | 3790 | You can also turn all of the transforms and ancillary chunk capabilities |
3791 | off en masse with compiler directives that define | 3791 | off en masse with compiler directives that define |
3792 | PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS, | 3792 | PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS, |
3793 | or all four, | 3793 | or all four, |
3794 | along with directives to turn on any of the capabilities that you do | 3794 | along with directives to turn on any of the capabilities that you do |
3795 | want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra | 3795 | want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra |
3796 | transformations but still leave the library fully capable of reading | 3796 | transformations but still leave the library fully capable of reading |
3797 | and writing PNG files with all known public chunks. Use of the | 3797 | and writing PNG files with all known public chunks. Use of the |
3798 | PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library | 3798 | PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library |
3799 | that is incapable of reading or writing ancillary chunks. If you are | 3799 | that is incapable of reading or writing ancillary chunks. If you are |
3800 | not using the progressive reading capability, you can turn that off | 3800 | not using the progressive reading capability, you can turn that off |
3801 | with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING | 3801 | with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING |
3802 | capability, which you'll still have). | 3802 | capability, which you'll still have). |
3803 | 3803 | ||
3804 | All the reading and writing specific code are in separate files, so the | 3804 | All the reading and writing specific code are in separate files, so the |
3805 | linker should only grab the files it needs. However, if you want to | 3805 | linker should only grab the files it needs. However, if you want to |
3806 | make sure, or if you are building a stand alone library, all the | 3806 | make sure, or if you are building a stand alone library, all the |
3807 | reading files start with "pngr" and all the writing files start with "pngw". | 3807 | reading files start with "pngr" and all the writing files start with "pngw". |
3808 | The files that don't match either (like png.c, pngtrans.c, etc.) | 3808 | The files that don't match either (like png.c, pngtrans.c, etc.) |
3809 | are used for both reading and writing, and always need to be included. | 3809 | are used for both reading and writing, and always need to be included. |
3810 | The progressive reader is in pngpread.c | 3810 | The progressive reader is in pngpread.c |
3811 | 3811 | ||
3812 | If you are creating or distributing a dynamically linked library (a .so | 3812 | If you are creating or distributing a dynamically linked library (a .so |
3813 | or DLL file), you should not remove or disable any parts of the library, | 3813 | or DLL file), you should not remove or disable any parts of the library, |
3814 | as this will cause applications linked with different versions of the | 3814 | as this will cause applications linked with different versions of the |
3815 | library to fail if they call functions not available in your library. | 3815 | library to fail if they call functions not available in your library. |
3816 | The size of the library itself should not be an issue, because only | 3816 | The size of the library itself should not be an issue, because only |
3817 | those sections that are actually used will be loaded into memory. | 3817 | those sections that are actually used will be loaded into memory. |
3818 | 3818 | ||
3819 | Requesting debug printout | 3819 | Requesting debug printout |
3820 | 3820 | ||
3821 | The macro definition PNG_DEBUG can be used to request debugging | 3821 | The macro definition PNG_DEBUG can be used to request debugging |
3822 | printout. Set it to an integer value in the range 0 to 3. Higher | 3822 | printout. Set it to an integer value in the range 0 to 3. Higher |
3823 | numbers result in increasing amounts of debugging information. The | 3823 | numbers result in increasing amounts of debugging information. The |
3824 | information is printed to the "stderr" file, unless another file | 3824 | information is printed to the "stderr" file, unless another file |
3825 | name is specified in the PNG_DEBUG_FILE macro definition. | 3825 | name is specified in the PNG_DEBUG_FILE macro definition. |
3826 | 3826 | ||
3827 | When PNG_DEBUG > 0, the following functions (macros) become available: | 3827 | When PNG_DEBUG > 0, the following functions (macros) become available: |
3828 | 3828 | ||
3829 | png_debug(level, message) | 3829 | png_debug(level, message) |
3830 | png_debug1(level, message, p1) | 3830 | png_debug1(level, message, p1) |
3831 | png_debug2(level, message, p1, p2) | 3831 | png_debug2(level, message, p1, p2) |
3832 | 3832 | ||
3833 | in which "level" is compared to PNG_DEBUG to decide whether to print | 3833 | in which "level" is compared to PNG_DEBUG to decide whether to print |
3834 | the message, "message" is the formatted string to be printed, | 3834 | the message, "message" is the formatted string to be printed, |
3835 | and p1 and p2 are parameters that are to be embedded in the string | 3835 | and p1 and p2 are parameters that are to be embedded in the string |
3836 | according to printf-style formatting directives. For example, | 3836 | according to printf-style formatting directives. For example, |
3837 | 3837 | ||
3838 | png_debug1(2, "foo=%d\n", foo); | 3838 | png_debug1(2, "foo=%d\n", foo); |
3839 | 3839 | ||
3840 | is expanded to | 3840 | is expanded to |
3841 | 3841 | ||
3842 | if (PNG_DEBUG > 2) | 3842 | if (PNG_DEBUG > 2) |
3843 | fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo); | 3843 | fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo); |
3844 | 3844 | ||
3845 | When PNG_DEBUG is defined but is zero, the macros aren't defined, but you | 3845 | When PNG_DEBUG is defined but is zero, the macros aren't defined, but you |
3846 | can still use PNG_DEBUG to control your own debugging: | 3846 | can still use PNG_DEBUG to control your own debugging: |
3847 | 3847 | ||
3848 | #ifdef PNG_DEBUG | 3848 | #ifdef PNG_DEBUG |
3849 | fprintf(stderr, ... | 3849 | fprintf(stderr, ... |
3850 | #endif | 3850 | #endif |
3851 | 3851 | ||
3852 | When PNG_DEBUG = 1, the macros are defined, but only png_debug statements | 3852 | When PNG_DEBUG = 1, the macros are defined, but only png_debug statements |
3853 | having level = 0 will be printed. There aren't any such statements in | 3853 | having level = 0 will be printed. There aren't any such statements in |
3854 | this version of libpng, but if you insert some they will be printed. | 3854 | this version of libpng, but if you insert some they will be printed. |
3855 | 3855 | ||
3856 | VI. MNG support | 3856 | VI. MNG support |
3857 | 3857 | ||
3858 | The MNG specification (available at http://www.libpng.org/pub/mng) allows | 3858 | The MNG specification (available at http://www.libpng.org/pub/mng) allows |
3859 | certain extensions to PNG for PNG images that are embedded in MNG datastreams. | 3859 | certain extensions to PNG for PNG images that are embedded in MNG datastreams. |
3860 | Libpng can support some of these extensions. To enable them, use the | 3860 | Libpng can support some of these extensions. To enable them, use the |
3861 | png_permit_mng_features() function: | 3861 | png_permit_mng_features() function: |
3862 | 3862 | ||
3863 | feature_set = png_permit_mng_features(png_ptr, mask) | 3863 | feature_set = png_permit_mng_features(png_ptr, mask) |
3864 | 3864 | ||
3865 | mask is a png_uint_32 containing the bitwise OR of the | 3865 | mask is a png_uint_32 containing the bitwise OR of the |
3866 | features you want to enable. These include | 3866 | features you want to enable. These include |
3867 | PNG_FLAG_MNG_EMPTY_PLTE | 3867 | PNG_FLAG_MNG_EMPTY_PLTE |
3868 | PNG_FLAG_MNG_FILTER_64 | 3868 | PNG_FLAG_MNG_FILTER_64 |
3869 | PNG_ALL_MNG_FEATURES | 3869 | PNG_ALL_MNG_FEATURES |
3870 | 3870 | ||
3871 | feature_set is a png_uint_32 that is the bitwise AND of | 3871 | feature_set is a png_uint_32 that is the bitwise AND of |
3872 | your mask with the set of MNG features that is | 3872 | your mask with the set of MNG features that is |
3873 | supported by the version of libpng that you are using. | 3873 | supported by the version of libpng that you are using. |
3874 | 3874 | ||
3875 | It is an error to use this function when reading or writing a standalone | 3875 | It is an error to use this function when reading or writing a standalone |
3876 | PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped | 3876 | PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped |
3877 | in a MNG datastream. As a minimum, it must have the MNG 8-byte signature | 3877 | in a MNG datastream. As a minimum, it must have the MNG 8-byte signature |
3878 | and the MHDR and MEND chunks. Libpng does not provide support for these | 3878 | and the MHDR and MEND chunks. Libpng does not provide support for these |
3879 | or any other MNG chunks; your application must provide its own support for | 3879 | or any other MNG chunks; your application must provide its own support for |
3880 | them. You may wish to consider using libmng (available at | 3880 | them. You may wish to consider using libmng (available at |
3881 | http://www.libmng.com) instead. | 3881 | http://www.libmng.com) instead. |
3882 | 3882 | ||
3883 | VII. Changes to Libpng from version 0.88 | 3883 | VII. Changes to Libpng from version 0.88 |
3884 | 3884 | ||
3885 | It should be noted that versions of libpng later than 0.96 are not | 3885 | It should be noted that versions of libpng later than 0.96 are not |
3886 | distributed by the original libpng author, Guy Schalnat, nor by | 3886 | distributed by the original libpng author, Guy Schalnat, nor by |
3887 | Andreas Dilger, who had taken over from Guy during 1996 and 1997, and | 3887 | Andreas Dilger, who had taken over from Guy during 1996 and 1997, and |
3888 | distributed versions 0.89 through 0.96, but rather by another member | 3888 | distributed versions 0.89 through 0.96, but rather by another member |
3889 | of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are | 3889 | of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are |
3890 | still alive and well, but they have moved on to other things. | 3890 | still alive and well, but they have moved on to other things. |
3891 | 3891 | ||
3892 | The old libpng functions png_read_init(), png_write_init(), | 3892 | The old libpng functions png_read_init(), png_write_init(), |
3893 | png_info_init(), png_read_destroy(), and png_write_destroy() have been | 3893 | png_info_init(), png_read_destroy(), and png_write_destroy() have been |
3894 | moved to PNG_INTERNAL in version 0.95 to discourage their use. These | 3894 | moved to PNG_INTERNAL in version 0.95 to discourage their use. These |
3895 | functions will be removed from libpng version 1.4.0. | 3895 | functions will be removed from libpng version 1.4.0. |
3896 | 3896 | ||
3897 | The preferred method of creating and initializing the libpng structures is | 3897 | The preferred method of creating and initializing the libpng structures is |
3898 | via the png_create_read_struct(), png_create_write_struct(), and | 3898 | via the png_create_read_struct(), png_create_write_struct(), and |
3899 | png_create_info_struct() because they isolate the size of the structures | 3899 | png_create_info_struct() because they isolate the size of the structures |
3900 | from the application, allow version error checking, and also allow the | 3900 | from the application, allow version error checking, and also allow the |
3901 | use of custom error handling routines during the initialization, which | 3901 | use of custom error handling routines during the initialization, which |
3902 | the old functions do not. The functions png_read_destroy() and | 3902 | the old functions do not. The functions png_read_destroy() and |
3903 | png_write_destroy() do not actually free the memory that libpng | 3903 | png_write_destroy() do not actually free the memory that libpng |
3904 | allocated for these structs, but just reset the data structures, so they | 3904 | allocated for these structs, but just reset the data structures, so they |
3905 | can be used instead of png_destroy_read_struct() and | 3905 | can be used instead of png_destroy_read_struct() and |
3906 | png_destroy_write_struct() if you feel there is too much system overhead | 3906 | png_destroy_write_struct() if you feel there is too much system overhead |
3907 | allocating and freeing the png_struct for each image read. | 3907 | allocating and freeing the png_struct for each image read. |
3908 | 3908 | ||
3909 | Setting the error callbacks via png_set_message_fn() before | 3909 | Setting the error callbacks via png_set_message_fn() before |
3910 | png_read_init() as was suggested in libpng-0.88 is no longer supported | 3910 | png_read_init() as was suggested in libpng-0.88 is no longer supported |
3911 | because this caused applications that do not use custom error functions | 3911 | because this caused applications that do not use custom error functions |
3912 | to fail if the png_ptr was not initialized to zero. It is still possible | 3912 | to fail if the png_ptr was not initialized to zero. It is still possible |
3913 | to set the error callbacks AFTER png_read_init(), or to change them with | 3913 | to set the error callbacks AFTER png_read_init(), or to change them with |
3914 | png_set_error_fn(), which is essentially the same function, but with a new | 3914 | png_set_error_fn(), which is essentially the same function, but with a new |
3915 | name to force compilation errors with applications that try to use the old | 3915 | name to force compilation errors with applications that try to use the old |
3916 | method. | 3916 | method. |
3917 | 3917 | ||
3918 | Starting with version 1.0.7, you can find out which version of the library | 3918 | Starting with version 1.0.7, you can find out which version of the library |
3919 | you are using at run-time: | 3919 | you are using at run-time: |
3920 | 3920 | ||
3921 | png_uint_32 libpng_vn = png_access_version_number(); | 3921 | png_uint_32 libpng_vn = png_access_version_number(); |
3922 | 3922 | ||
3923 | The number libpng_vn is constructed from the major version, minor | 3923 | The number libpng_vn is constructed from the major version, minor |
3924 | version with leading zero, and release number with leading zero, | 3924 | version with leading zero, and release number with leading zero, |
3925 | (e.g., libpng_vn for version 1.0.7 is 10007). | 3925 | (e.g., libpng_vn for version 1.0.7 is 10007). |
3926 | 3926 | ||
3927 | Note that this function does not take a png_ptr, so you can call it | 3927 | Note that this function does not take a png_ptr, so you can call it |
3928 | before you've created one. | 3928 | before you've created one. |
3929 | 3929 | ||
3930 | You can also check which version of png.h you used when compiling your | 3930 | You can also check which version of png.h you used when compiling your |
3931 | application: | 3931 | application: |
3932 | 3932 | ||
3933 | png_uint_32 application_vn = PNG_LIBPNG_VER; | 3933 | png_uint_32 application_vn = PNG_LIBPNG_VER; |
3934 | 3934 | ||
3935 | VIII. Changes to Libpng from version 1.0.x to 1.2.x | 3935 | VIII. Changes to Libpng from version 1.0.x to 1.2.x |
3936 | 3936 | ||
3937 | Support for user memory management was enabled by default. To | 3937 | Support for user memory management was enabled by default. To |
3938 | accomplish this, the functions png_create_read_struct_2(), | 3938 | accomplish this, the functions png_create_read_struct_2(), |
3939 | png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(), | 3939 | png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(), |
3940 | png_malloc_default(), and png_free_default() were added. | 3940 | png_malloc_default(), and png_free_default() were added. |
3941 | 3941 | ||
3942 | Support for the iTXt chunk has been enabled by default as of | 3942 | Support for the iTXt chunk has been enabled by default as of |
3943 | version 1.2.41. | 3943 | version 1.2.41. |
3944 | 3944 | ||
3945 | Support for certain MNG features was enabled. | 3945 | Support for certain MNG features was enabled. |
3946 | 3946 | ||
3947 | Support for numbered error messages was added. However, we never got | 3947 | Support for numbered error messages was added. However, we never got |
3948 | around to actually numbering the error messages. The function | 3948 | around to actually numbering the error messages. The function |
3949 | png_set_strip_error_numbers() was added (Note: the prototype for this | 3949 | png_set_strip_error_numbers() was added (Note: the prototype for this |
3950 | function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE | 3950 | function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE |
3951 | builds of libpng-1.2.15. It was restored in libpng-1.2.36). | 3951 | builds of libpng-1.2.15. It was restored in libpng-1.2.36). |
3952 | 3952 | ||
3953 | The png_malloc_warn() function was added at libpng-1.2.3. This issues | 3953 | The png_malloc_warn() function was added at libpng-1.2.3. This issues |
3954 | a png_warning and returns NULL instead of aborting when it fails to | 3954 | a png_warning and returns NULL instead of aborting when it fails to |
3955 | acquire the requested memory allocation. | 3955 | acquire the requested memory allocation. |
3956 | 3956 | ||
3957 | Support for setting user limits on image width and height was enabled | 3957 | Support for setting user limits on image width and height was enabled |
3958 | by default. The functions png_set_user_limits(), png_get_user_width_max(), | 3958 | by default. The functions png_set_user_limits(), png_get_user_width_max(), |
3959 | and png_get_user_height_max() were added at libpng-1.2.6. | 3959 | and png_get_user_height_max() were added at libpng-1.2.6. |
3960 | 3960 | ||
3961 | The png_set_add_alpha() function was added at libpng-1.2.7. | 3961 | The png_set_add_alpha() function was added at libpng-1.2.7. |
3962 | 3962 | ||
3963 | The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9. | 3963 | The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9. |
3964 | Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the | 3964 | Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the |
3965 | tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is | 3965 | tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is |
3966 | deprecated. | 3966 | deprecated. |
3967 | 3967 | ||
3968 | A number of macro definitions in support of runtime selection of | 3968 | A number of macro definitions in support of runtime selection of |
3969 | assembler code features (especially Intel MMX code support) were | 3969 | assembler code features (especially Intel MMX code support) were |
3970 | added at libpng-1.2.0: | 3970 | added at libpng-1.2.0: |
3971 | 3971 | ||
3972 | PNG_ASM_FLAG_MMX_SUPPORT_COMPILED | 3972 | PNG_ASM_FLAG_MMX_SUPPORT_COMPILED |
3973 | PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU | 3973 | PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU |
3974 | PNG_ASM_FLAG_MMX_READ_COMBINE_ROW | 3974 | PNG_ASM_FLAG_MMX_READ_COMBINE_ROW |
3975 | PNG_ASM_FLAG_MMX_READ_INTERLACE | 3975 | PNG_ASM_FLAG_MMX_READ_INTERLACE |
3976 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB | 3976 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB |
3977 | PNG_ASM_FLAG_MMX_READ_FILTER_UP | 3977 | PNG_ASM_FLAG_MMX_READ_FILTER_UP |
3978 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG | 3978 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG |
3979 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH | 3979 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH |
3980 | PNG_ASM_FLAGS_INITIALIZED | 3980 | PNG_ASM_FLAGS_INITIALIZED |
3981 | PNG_MMX_READ_FLAGS | 3981 | PNG_MMX_READ_FLAGS |
3982 | PNG_MMX_FLAGS | 3982 | PNG_MMX_FLAGS |
3983 | PNG_MMX_WRITE_FLAGS | 3983 | PNG_MMX_WRITE_FLAGS |
3984 | PNG_MMX_FLAGS | 3984 | PNG_MMX_FLAGS |
3985 | 3985 | ||
3986 | We added the following functions in support of runtime | 3986 | We added the following functions in support of runtime |
3987 | selection of assembler code features: | 3987 | selection of assembler code features: |
3988 | 3988 | ||
3989 | png_get_mmx_flagmask() | 3989 | png_get_mmx_flagmask() |
3990 | png_set_mmx_thresholds() | 3990 | png_set_mmx_thresholds() |
3991 | png_get_asm_flags() | 3991 | png_get_asm_flags() |
3992 | png_get_mmx_bitdepth_threshold() | 3992 | png_get_mmx_bitdepth_threshold() |
3993 | png_get_mmx_rowbytes_threshold() | 3993 | png_get_mmx_rowbytes_threshold() |
3994 | png_set_asm_flags() | 3994 | png_set_asm_flags() |
3995 | 3995 | ||
3996 | We replaced all of these functions with simple stubs in libpng-1.2.20, | 3996 | We replaced all of these functions with simple stubs in libpng-1.2.20, |
3997 | when the Intel assembler code was removed due to a licensing issue. | 3997 | when the Intel assembler code was removed due to a licensing issue. |
3998 | 3998 | ||
3999 | These macros are deprecated: | 3999 | These macros are deprecated: |
4000 | 4000 | ||
4001 | PNG_READ_TRANSFORMS_NOT_SUPPORTED | 4001 | PNG_READ_TRANSFORMS_NOT_SUPPORTED |
4002 | PNG_PROGRESSIVE_READ_NOT_SUPPORTED | 4002 | PNG_PROGRESSIVE_READ_NOT_SUPPORTED |
4003 | PNG_NO_SEQUENTIAL_READ_SUPPORTED | 4003 | PNG_NO_SEQUENTIAL_READ_SUPPORTED |
4004 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED | 4004 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED |
4005 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED | 4005 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED |
4006 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED | 4006 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED |
4007 | 4007 | ||
4008 | They have been replaced, respectively, by: | 4008 | They have been replaced, respectively, by: |
4009 | 4009 | ||
4010 | PNG_NO_READ_TRANSFORMS | 4010 | PNG_NO_READ_TRANSFORMS |
4011 | PNG_NO_PROGRESSIVE_READ | 4011 | PNG_NO_PROGRESSIVE_READ |
4012 | PNG_NO_SEQUENTIAL_READ | 4012 | PNG_NO_SEQUENTIAL_READ |
4013 | PNG_NO_WRITE_TRANSFORMS | 4013 | PNG_NO_WRITE_TRANSFORMS |
4014 | PNG_NO_READ_ANCILLARY_CHUNKS | 4014 | PNG_NO_READ_ANCILLARY_CHUNKS |
4015 | PNG_NO_WRITE_ANCILLARY_CHUNKS | 4015 | PNG_NO_WRITE_ANCILLARY_CHUNKS |
4016 | 4016 | ||
4017 | PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been | 4017 | PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been |
4018 | deprecated since libpng-1.0.16 and libpng-1.2.6. | 4018 | deprecated since libpng-1.0.16 and libpng-1.2.6. |
4019 | 4019 | ||
4020 | The function | 4020 | The function |
4021 | png_check_sig(sig, num) | 4021 | png_check_sig(sig, num) |
4022 | was replaced with | 4022 | was replaced with |
4023 | !png_sig_cmp(sig, 0, num) | 4023 | !png_sig_cmp(sig, 0, num) |
4024 | It has been deprecated since libpng-0.90. | 4024 | It has been deprecated since libpng-0.90. |
4025 | 4025 | ||
4026 | The function | 4026 | The function |
4027 | png_set_gray_1_2_4_to_8() | 4027 | png_set_gray_1_2_4_to_8() |
4028 | which also expands tRNS to alpha was replaced with | 4028 | which also expands tRNS to alpha was replaced with |
4029 | png_set_expand_gray_1_2_4_to_8() | 4029 | png_set_expand_gray_1_2_4_to_8() |
4030 | which does not. It has been deprecated since libpng-1.0.18 and 1.2.9. | 4030 | which does not. It has been deprecated since libpng-1.0.18 and 1.2.9. |
4031 | 4031 | ||
4032 | IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x | 4032 | IX. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x |
4033 | 4033 | ||
4034 | Private libpng prototypes and macro definitions were moved from | 4034 | Private libpng prototypes and macro definitions were moved from |
4035 | png.h and pngconf.h into a new pngpriv.h header file. | 4035 | png.h and pngconf.h into a new pngpriv.h header file. |
4036 | 4036 | ||
4037 | Functions png_set_benign_errors(), png_benign_error(), and | 4037 | Functions png_set_benign_errors(), png_benign_error(), and |
4038 | png_chunk_benign_error() were added. | 4038 | png_chunk_benign_error() were added. |
4039 | 4039 | ||
4040 | Support for setting the maximum amount of memory that the application | 4040 | Support for setting the maximum amount of memory that the application |
4041 | will allocate for reading chunks was added, as a security measure. | 4041 | will allocate for reading chunks was added, as a security measure. |
4042 | The functions png_set_chunk_cache_max() and png_get_chunk_cache_max() | 4042 | The functions png_set_chunk_cache_max() and png_get_chunk_cache_max() |
4043 | were added to the library. | 4043 | were added to the library. |
4044 | 4044 | ||
4045 | We implemented support for I/O states by adding png_ptr member io_state | 4045 | We implemented support for I/O states by adding png_ptr member io_state |
4046 | and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c | 4046 | and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c |
4047 | 4047 | ||
4048 | We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level | 4048 | We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level |
4049 | input transforms. | 4049 | input transforms. |
4050 | 4050 | ||
4051 | Checking for and reporting of errors in the IHDR chunk is more thorough. | 4051 | Checking for and reporting of errors in the IHDR chunk is more thorough. |
4052 | 4052 | ||
4053 | Support for global arrays was removed, to improve thread safety. | 4053 | Support for global arrays was removed, to improve thread safety. |
4054 | 4054 | ||
4055 | Some obsolete/deprecated macros and functions have been removed. | 4055 | Some obsolete/deprecated macros and functions have been removed. |
4056 | 4056 | ||
4057 | Typecasted NULL definitions such as | 4057 | Typecasted NULL definitions such as |
4058 | #define png_voidp_NULL (png_voidp)NULL | 4058 | #define png_voidp_NULL (png_voidp)NULL |
4059 | were eliminated. If you used these in your application, just use | 4059 | were eliminated. If you used these in your application, just use |
4060 | NULL instead. | 4060 | NULL instead. |
4061 | 4061 | ||
4062 | The png_struct and info_struct members "trans" and "trans_values" were | 4062 | The png_struct and info_struct members "trans" and "trans_values" were |
4063 | changed to "trans_alpha" and "trans_color", respectively. | 4063 | changed to "trans_alpha" and "trans_color", respectively. |
4064 | 4064 | ||
4065 | The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles | 4065 | The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles |
4066 | were removed. | 4066 | were removed. |
4067 | 4067 | ||
4068 | The PNG_1_0_X and PNG_1_2_X macros were eliminated. | 4068 | The PNG_1_0_X and PNG_1_2_X macros were eliminated. |
4069 | 4069 | ||
4070 | The PNG_LEGACY_SUPPORTED macro was eliminated. | 4070 | The PNG_LEGACY_SUPPORTED macro was eliminated. |
4071 | 4071 | ||
4072 | Many WIN32_WCE #ifdefs were removed. | 4072 | Many WIN32_WCE #ifdefs were removed. |
4073 | 4073 | ||
4074 | The functions png_read_init(info_ptr), png_write_init(info_ptr), | 4074 | The functions png_read_init(info_ptr), png_write_init(info_ptr), |
4075 | png_info_init(info_ptr), png_read_destroy(), and png_write_destroy() | 4075 | png_info_init(info_ptr), png_read_destroy(), and png_write_destroy() |
4076 | have been removed. They have been deprecated since libpng-0.95. | 4076 | have been removed. They have been deprecated since libpng-0.95. |
4077 | 4077 | ||
4078 | The png_permit_empty_plte() was removed. It has been deprecated | 4078 | The png_permit_empty_plte() was removed. It has been deprecated |
4079 | since libpng-1.0.9. Use png_permit_mng_features() instead. | 4079 | since libpng-1.0.9. Use png_permit_mng_features() instead. |
4080 | 4080 | ||
4081 | We removed the obsolete stub functions png_get_mmx_flagmask(), | 4081 | We removed the obsolete stub functions png_get_mmx_flagmask(), |
4082 | png_set_mmx_thresholds(), png_get_asm_flags(), | 4082 | png_set_mmx_thresholds(), png_get_asm_flags(), |
4083 | png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(), | 4083 | png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(), |
4084 | png_set_asm_flags(), and png_mmx_supported() | 4084 | png_set_asm_flags(), and png_mmx_supported() |
4085 | 4085 | ||
4086 | We removed the obsolete png_check_sig(), png_memcpy_check(), and | 4086 | We removed the obsolete png_check_sig(), png_memcpy_check(), and |
4087 | png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(), | 4087 | png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(), |
4088 | and memset(), respectively. | 4088 | and memset(), respectively. |
4089 | 4089 | ||
4090 | The function png_set_gray_1_2_4_to_8() was removed. It has been | 4090 | The function png_set_gray_1_2_4_to_8() was removed. It has been |
4091 | deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with | 4091 | deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with |
4092 | png_set_expand_gray_1_2_4_to_8() because the former function also | 4092 | png_set_expand_gray_1_2_4_to_8() because the former function also |
4093 | expanded any tRNS chunk to an alpha channel. | 4093 | expanded any tRNS chunk to an alpha channel. |
4094 | 4094 | ||
4095 | Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32 | 4095 | Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32 |
4096 | were added and are used by default instead of the corresponding | 4096 | were added and are used by default instead of the corresponding |
4097 | functions. Unfortunately, | 4097 | functions. Unfortunately, |
4098 | from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the | 4098 | from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the |
4099 | function) incorrectly returned a value of type png_uint_32. | 4099 | function) incorrectly returned a value of type png_uint_32. |
4100 | 4100 | ||
4101 | We changed the prototype for png_malloc() from | 4101 | We changed the prototype for png_malloc() from |
4102 | png_malloc(png_structp png_ptr, png_uint_32 size) | 4102 | png_malloc(png_structp png_ptr, png_uint_32 size) |
4103 | to | 4103 | to |
4104 | png_malloc(png_structp png_ptr, png_alloc_size_t size) | 4104 | png_malloc(png_structp png_ptr, png_alloc_size_t size) |
4105 | 4105 | ||
4106 | This also applies to the prototype for the user replacement malloc_fn(). | 4106 | This also applies to the prototype for the user replacement malloc_fn(). |
4107 | 4107 | ||
4108 | The png_calloc() function was added and is used in place of | 4108 | The png_calloc() function was added and is used in place of |
4109 | of "png_malloc(); memset();" except in the case in png_read_png() | 4109 | of "png_malloc(); memset();" except in the case in png_read_png() |
4110 | where the array consists of pointers; in this case a "for" loop is used | 4110 | where the array consists of pointers; in this case a "for" loop is used |
4111 | after the png_malloc() to set the pointers to NULL, to give robust. | 4111 | after the png_malloc() to set the pointers to NULL, to give robust. |
4112 | behavior in case the application runs out of memory part-way through | 4112 | behavior in case the application runs out of memory part-way through |
4113 | the process. | 4113 | the process. |
4114 | 4114 | ||
4115 | We changed the prototypes of png_get_compression_buffer_size() and | 4115 | We changed the prototypes of png_get_compression_buffer_size() and |
4116 | png_set_compression_buffer_size() to work with png_size_t instead of | 4116 | png_set_compression_buffer_size() to work with png_size_t instead of |
4117 | png_uint_32. | 4117 | png_uint_32. |
4118 | 4118 | ||
4119 | Support for numbered error messages was removed by default, since we | 4119 | Support for numbered error messages was removed by default, since we |
4120 | never got around to actually numbering the error messages. The function | 4120 | never got around to actually numbering the error messages. The function |
4121 | png_set_strip_error_numbers() was removed from the library by default. | 4121 | png_set_strip_error_numbers() was removed from the library by default. |
4122 | 4122 | ||
4123 | The png_zalloc() and png_zfree() functions are no longer exported. | 4123 | The png_zalloc() and png_zfree() functions are no longer exported. |
4124 | The png_zalloc() function no longer zeroes out the memory that it | 4124 | The png_zalloc() function no longer zeroes out the memory that it |
4125 | allocates. | 4125 | allocates. |
4126 | 4126 | ||
4127 | Support for dithering was disabled by default in libpng-1.4.0, because | 4127 | Support for dithering was disabled by default in libpng-1.4.0, because |
4128 | it has not been well tested and doesn't actually "dither". | 4128 | it has not been well tested and doesn't actually "dither". |
4129 | The code was not | 4129 | The code was not |
4130 | removed, however, and could be enabled by building libpng with | 4130 | removed, however, and could be enabled by building libpng with |
4131 | PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support | 4131 | PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support |
4132 | was reenabled, but the function was renamed png_set_quantize() to | 4132 | was reenabled, but the function was renamed png_set_quantize() to |
4133 | reflect more accurately what it actually does. At the same time, | 4133 | reflect more accurately what it actually does. At the same time, |
4134 | the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to | 4134 | the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to |
4135 | PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED | 4135 | PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED |
4136 | was renamed to PNG_READ_QUANTIZE_SUPPORTED. | 4136 | was renamed to PNG_READ_QUANTIZE_SUPPORTED. |
4137 | 4137 | ||
4138 | We removed the trailing '.' from the warning and error messages. | 4138 | We removed the trailing '.' from the warning and error messages. |
4139 | 4139 | ||
4140 | X. Changes to Libpng from version 1.4.x to 1.5.x | 4140 | X. Changes to Libpng from version 1.4.x to 1.5.x |
4141 | 4141 | ||
4142 | From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the | 4142 | From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the |
4143 | function) incorrectly returned a value of type png_uint_32. | 4143 | function) incorrectly returned a value of type png_uint_32. |
4144 | 4144 | ||
4145 | A. Changes that affect users of libpng | 4145 | A. Changes that affect users of libpng |
4146 | 4146 | ||
4147 | There are no substantial API changes between the non-deprecated parts of | 4147 | There are no substantial API changes between the non-deprecated parts of |
4148 | the 1.4.5 API and the 1.5.0 API, however the ability to directly access | 4148 | the 1.4.5 API and the 1.5.0 API, however the ability to directly access |
4149 | the main libpng control structures, png_struct and png_info, deprecated | 4149 | the main libpng control structures, png_struct and png_info, deprecated |
4150 | in earlier versions of libpng, has been completely removed from | 4150 | in earlier versions of libpng, has been completely removed from |
4151 | libpng 1.5. | 4151 | libpng 1.5. |
4152 | 4152 | ||
4153 | We no longer include zlib.h in png.h. Applications that need access | 4153 | We no longer include zlib.h in png.h. Applications that need access |
4154 | to information in zlib.h will need to add the '#include "zlib.h"' | 4154 | to information in zlib.h will need to add the '#include "zlib.h"' |
4155 | directive. It does not matter whether it is placed prior to or after | 4155 | directive. It does not matter whether it is placed prior to or after |
4156 | the '"#include png.h"' directive. | 4156 | the '"#include png.h"' directive. |
4157 | 4157 | ||
4158 | We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(), | 4158 | We moved the png_strcpy(), png_strncpy(), png_strlen(), png_memcpy(), |
4159 | png_memcmp(), png_sprintf, and png_memcpy() macros into a private | 4159 | png_memcmp(), png_sprintf, and png_memcpy() macros into a private |
4160 | header file (pngpriv.h) that is not accessible to applications. | 4160 | header file (pngpriv.h) that is not accessible to applications. |
4161 | 4161 | ||
4162 | In png_get_iCCP, the type of "profile" was changed from png_charpp | 4162 | In png_get_iCCP, the type of "profile" was changed from png_charpp |
4163 | to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep. | 4163 | to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep. |
4164 | 4164 | ||
4165 | There are changes of form in png.h, including new and changed macros to | 4165 | There are changes of form in png.h, including new and changed macros to |
4166 | declare parts of the API. Some API functions with arguments that are | 4166 | declare parts of the API. Some API functions with arguments that are |
4167 | pointers to data not modified within the function have been corrected to | 4167 | pointers to data not modified within the function have been corrected to |
4168 | declare these arguments with PNG_CONST. | 4168 | declare these arguments with PNG_CONST. |
4169 | 4169 | ||
4170 | Much of the internal use of C macros to control the library build has also | 4170 | Much of the internal use of C macros to control the library build has also |
4171 | changed and some of this is visible in the exported header files, in | 4171 | changed and some of this is visible in the exported header files, in |
4172 | particular the use of macros to control data and API elements visible | 4172 | particular the use of macros to control data and API elements visible |
4173 | during application compilation may require significant revision to | 4173 | during application compilation may require significant revision to |
4174 | application code. (It is extremely rare for an application to do this.) | 4174 | application code. (It is extremely rare for an application to do this.) |
4175 | 4175 | ||
4176 | Any program that compiled against libpng 1.4 and did not use deprecated | 4176 | Any program that compiled against libpng 1.4 and did not use deprecated |
4177 | features or access internal library structures should compile and work | 4177 | features or access internal library structures should compile and work |
4178 | against libpng 1.5, except for the change in the prototype for | 4178 | against libpng 1.5, except for the change in the prototype for |
4179 | png_get_iCCP() and png_set_iCCP() API functions mentioned above. | 4179 | png_get_iCCP() and png_set_iCCP() API functions mentioned above. |
4180 | 4180 | ||
4181 | libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of | 4181 | libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of |
4182 | interlaced images. The macros return the number of rows and columns in | 4182 | interlaced images. The macros return the number of rows and columns in |
4183 | each pass and information that can be used to de-interlace and (if | 4183 | each pass and information that can be used to de-interlace and (if |
4184 | absolutely necessary) interlace an image. | 4184 | absolutely necessary) interlace an image. |
4185 | 4185 | ||
4186 | libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls | 4186 | libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls |
4187 | the application-provided png_longjmp_ptr on the internal, but application | 4187 | the application-provided png_longjmp_ptr on the internal, but application |
4188 | initialized, longjmp buffer. It is provided as a convenience to avoid | 4188 | initialized, longjmp buffer. It is provided as a convenience to avoid |
4189 | the need to use the png_jmpbuf macro, which had the unnecessary side | 4189 | the need to use the png_jmpbuf macro, which had the unnecessary side |
4190 | effect of resetting the internal png_longjmp_ptr value. | 4190 | effect of resetting the internal png_longjmp_ptr value. |
4191 | 4191 | ||
4192 | libpng 1.5.0 includes a complete fixed point API. By default this is | 4192 | libpng 1.5.0 includes a complete fixed point API. By default this is |
4193 | present along with the corresponding floating point API. In general the | 4193 | present along with the corresponding floating point API. In general the |
4194 | fixed point API is faster and smaller than the floating point one because | 4194 | fixed point API is faster and smaller than the floating point one because |
4195 | the PNG file format used fixed point, not floating point. This applies | 4195 | the PNG file format used fixed point, not floating point. This applies |
4196 | even if the library uses floating point in internal calculations. A new | 4196 | even if the library uses floating point in internal calculations. A new |
4197 | macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library | 4197 | macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library |
4198 | uses floating point arithmetic (the default) or fixed point arithmetic | 4198 | uses floating point arithmetic (the default) or fixed point arithmetic |
4199 | internally for performance critical calculations such as gamma correction. | 4199 | internally for performance critical calculations such as gamma correction. |
4200 | In some cases, the gamma calculations may produce slightly different | 4200 | In some cases, the gamma calculations may produce slightly different |
4201 | results. This has changed the results in png_rgb_to_gray and in alpha | 4201 | results. This has changed the results in png_rgb_to_gray and in alpha |
4202 | composition (png_set_background for example). This applies even if the | 4202 | composition (png_set_background for example). This applies even if the |
4203 | original image was already linear (gamma == 1.0) and, therefore, it is | 4203 | original image was already linear (gamma == 1.0) and, therefore, it is |
4204 | not necessary to linearize the image. This is because libpng has *not* | 4204 | not necessary to linearize the image. This is because libpng has *not* |
4205 | been changed to optimize that case correctly, yet. | 4205 | been changed to optimize that case correctly, yet. |
4206 | 4206 | ||
4207 | Fixed point support for the sCAL chunk comes with an important caveat; | 4207 | Fixed point support for the sCAL chunk comes with an important caveat; |
4208 | the sCAL specification uses a decimal encoding of floating point values | 4208 | the sCAL specification uses a decimal encoding of floating point values |
4209 | and the accuracy of PNG fixed point values is insufficient for | 4209 | and the accuracy of PNG fixed point values is insufficient for |
4210 | representation of these values. Consequently a "string" API | 4210 | representation of these values. Consequently a "string" API |
4211 | (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading | 4211 | (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading |
4212 | arbitrary sCAL chunks in the absence of either the floating point API or | 4212 | arbitrary sCAL chunks in the absence of either the floating point API or |
4213 | internal floating point calculations. | 4213 | internal floating point calculations. |
4214 | 4214 | ||
4215 | Applications no longer need to include the optional distribution header | 4215 | Applications no longer need to include the optional distribution header |
4216 | file pngusr.h or define the corresponding macros during application | 4216 | file pngusr.h or define the corresponding macros during application |
4217 | build in order to see the correct variant of the libpng API. From 1.5.0 | 4217 | build in order to see the correct variant of the libpng API. From 1.5.0 |
4218 | application code can check for the corresponding _SUPPORTED macro: | 4218 | application code can check for the corresponding _SUPPORTED macro: |
4219 | 4219 | ||
4220 | #ifdef PNG_INCH_CONVERSIONS_SUPPORTED | 4220 | #ifdef PNG_INCH_CONVERSIONS_SUPPORTED |
4221 | /* code that uses the inch conversion APIs. */ | 4221 | /* code that uses the inch conversion APIs. */ |
4222 | #endif | 4222 | #endif |
4223 | 4223 | ||
4224 | This macro will only be defined if the inch conversion functions have been | 4224 | This macro will only be defined if the inch conversion functions have been |
4225 | compiled into libpng. The full set of macros, and whether or not support | 4225 | compiled into libpng. The full set of macros, and whether or not support |
4226 | has been compiled in, are available in the header file pnglibconf.h. | 4226 | has been compiled in, are available in the header file pnglibconf.h. |
4227 | This header file is specific to the libpng build. Notice that prior to | 4227 | This header file is specific to the libpng build. Notice that prior to |
4228 | 1.5.0 the _SUPPORTED macros would always have the default definition unless | 4228 | 1.5.0 the _SUPPORTED macros would always have the default definition unless |
4229 | reset by pngusr.h or by explicit settings on the compiler command line. | 4229 | reset by pngusr.h or by explicit settings on the compiler command line. |
4230 | These settings may produce compiler warnings or errors in 1.5.0 because | 4230 | These settings may produce compiler warnings or errors in 1.5.0 because |
4231 | of macro redefinition. | 4231 | of macro redefinition. |
4232 | 4232 | ||
4233 | From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the | 4233 | From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the |
4234 | function) incorrectly returned a value of type png_uint_32. libpng 1.5.0 | 4234 | function) incorrectly returned a value of type png_uint_32. libpng 1.5.0 |
4235 | is consistent with the implementation in 1.4.5 and 1.2.x (where the macro | 4235 | is consistent with the implementation in 1.4.5 and 1.2.x (where the macro |
4236 | did not exist.) | 4236 | did not exist.) |
4237 | 4237 | ||
4238 | Applications can now choose whether to use these macros or to call the | 4238 | Applications can now choose whether to use these macros or to call the |
4239 | corresponding function by defining PNG_USE_READ_MACROS or | 4239 | corresponding function by defining PNG_USE_READ_MACROS or |
4240 | PNG_NO_USE_READ_MACROS before including png.h. Notice that this is | 4240 | PNG_NO_USE_READ_MACROS before including png.h. Notice that this is |
4241 | only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0 | 4241 | only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0 |
4242 | will lead to a link failure. | 4242 | will lead to a link failure. |
4243 | 4243 | ||
4244 | Prior to libpng-1.5.4, the zlib compressor used the same set of parameters | 4244 | Prior to libpng-1.5.4, the zlib compressor used the same set of parameters |
4245 | when compressing the IDAT data and textual data such as zTXt and iCCP. | 4245 | when compressing the IDAT data and textual data such as zTXt and iCCP. |
4246 | In libpng-1.5.4 we reinitialized the zlib stream for each type of data. | 4246 | In libpng-1.5.4 we reinitialized the zlib stream for each type of data. |
4247 | We added five png_set_text_*() functions for setting the parameters to | 4247 | We added five png_set_text_*() functions for setting the parameters to |
4248 | use with textual data. | 4248 | use with textual data. |
4249 | 4249 | ||
4250 | Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED | 4250 | Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED |
4251 | option was off by default, and slightly inaccurate scaling occurred. | 4251 | option was off by default, and slightly inaccurate scaling occurred. |
4252 | This option can no longer be turned off, and the choice of accurate | 4252 | This option can no longer be turned off, and the choice of accurate |
4253 | or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8() | 4253 | or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8() |
4254 | API for accurate scaling or the old png_set_strip_16_to_8() API for simple | 4254 | API for accurate scaling or the old png_set_strip_16_to_8() API for simple |
4255 | chopping. | 4255 | chopping. |
4256 | 4256 | ||
4257 | Prior to libpng-1.5.4, the png_set_user_limits() function could only be | 4257 | Prior to libpng-1.5.4, the png_set_user_limits() function could only be |
4258 | used to reduce the width and height limits from the value of | 4258 | used to reduce the width and height limits from the value of |
4259 | PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said | 4259 | PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said |
4260 | that it could be used to override them. Now this function will reduce or | 4260 | that it could be used to override them. Now this function will reduce or |
4261 | increase the limits. | 4261 | increase the limits. |
4262 | 4262 | ||
4263 | B. Changes to the build and configuration of libpng | 4263 | B. Changes to the build and configuration of libpng |
4264 | 4264 | ||
4265 | Details of internal changes to the library code can be found in the CHANGES | 4265 | Details of internal changes to the library code can be found in the CHANGES |
4266 | file and in the GIT repository logs. These will be of no concern to the vast | 4266 | file and in the GIT repository logs. These will be of no concern to the vast |
4267 | majority of library users or builders, however the few who configure libpng | 4267 | majority of library users or builders, however the few who configure libpng |
4268 | to a non-default feature set may need to change how this is done. | 4268 | to a non-default feature set may need to change how this is done. |
4269 | 4269 | ||
4270 | There should be no need for library builders to alter build scripts if | 4270 | There should be no need for library builders to alter build scripts if |
4271 | these use the distributed build support - configure or the makefiles - | 4271 | these use the distributed build support - configure or the makefiles - |
4272 | however users of the makefiles may care to update their build scripts | 4272 | however users of the makefiles may care to update their build scripts |
4273 | to build pnglibconf.h where the corresponding makefile does not do so. | 4273 | to build pnglibconf.h where the corresponding makefile does not do so. |
4274 | 4274 | ||
4275 | Building libpng with a non-default configuration has changed completely. | 4275 | Building libpng with a non-default configuration has changed completely. |
4276 | The old method using pngusr.h should still work correctly even though the | 4276 | The old method using pngusr.h should still work correctly even though the |
4277 | way pngusr.h is used in the build has been changed; however, library | 4277 | way pngusr.h is used in the build has been changed; however, library |
4278 | builders will probably want to examine the changes to take advantage of | 4278 | builders will probably want to examine the changes to take advantage of |
4279 | new capabilities and to simplify their build system. | 4279 | new capabilities and to simplify their build system. |
4280 | 4280 | ||
4281 | B.1 Specific changes to library configuration capabilities | 4281 | B.1 Specific changes to library configuration capabilities |
4282 | 4282 | ||
4283 | The library now supports a complete fixed point implementation and can | 4283 | The library now supports a complete fixed point implementation and can |
4284 | thus be used on systems that have no floating point support or very | 4284 | thus be used on systems that have no floating point support or very |
4285 | limited or slow support. Previously gamma correction, an essential part | 4285 | limited or slow support. Previously gamma correction, an essential part |
4286 | of complete PNG support, required reasonably fast floating point. | 4286 | of complete PNG support, required reasonably fast floating point. |
4287 | 4287 | ||
4288 | As part of this the choice of internal implementation has been made | 4288 | As part of this the choice of internal implementation has been made |
4289 | independent of the choice of fixed versus floating point APIs and all the | 4289 | independent of the choice of fixed versus floating point APIs and all the |
4290 | missing fixed point APIs have been implemented. | 4290 | missing fixed point APIs have been implemented. |
4291 | 4291 | ||
4292 | The exact mechanism used to control attributes of API functions has | 4292 | The exact mechanism used to control attributes of API functions has |
4293 | changed. A single set of operating system independent macro definitions | 4293 | changed. A single set of operating system independent macro definitions |
4294 | is used and operating system specific directives are defined in | 4294 | is used and operating system specific directives are defined in |
4295 | pnglibconf.h | 4295 | pnglibconf.h |
4296 | 4296 | ||
4297 | As part of this the mechanism used to choose procedure call standards on | 4297 | As part of this the mechanism used to choose procedure call standards on |
4298 | those systems that allow a choice has been changed. At present this only | 4298 | those systems that allow a choice has been changed. At present this only |
4299 | affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems | 4299 | affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems |
4300 | running on Intel processors. As before, PNGAPI is defined where required | 4300 | running on Intel processors. As before, PNGAPI is defined where required |
4301 | to control the exported API functions; however, two new macros, PNGCBAPI | 4301 | to control the exported API functions; however, two new macros, PNGCBAPI |
4302 | and PNGCAPI, are used instead for callback functions (PNGCBAPI) and | 4302 | and PNGCAPI, are used instead for callback functions (PNGCBAPI) and |
4303 | (PNGCAPI) for functions that must match a C library prototype (currently | 4303 | (PNGCAPI) for functions that must match a C library prototype (currently |
4304 | only png_longjmp_ptr, which must match the C longjmp function.) The new | 4304 | only png_longjmp_ptr, which must match the C longjmp function.) The new |
4305 | approach is documented in pngconf.h | 4305 | approach is documented in pngconf.h |
4306 | 4306 | ||
4307 | Despite these changes, libpng 1.5.0 only supports the native C function | 4307 | Despite these changes, libpng 1.5.0 only supports the native C function |
4308 | calling standard on those platforms tested so far (__cdecl on Microsoft | 4308 | calling standard on those platforms tested so far (__cdecl on Microsoft |
4309 | Windows). This is because the support requirements for alternative | 4309 | Windows). This is because the support requirements for alternative |
4310 | calling conventions seem to no longer exist. Developers who find it | 4310 | calling conventions seem to no longer exist. Developers who find it |
4311 | necessary to set PNG_API_RULE to 1 should advise the mailing list | 4311 | necessary to set PNG_API_RULE to 1 should advise the mailing list |
4312 | (png-mng-implement) of this and library builders who use Openwatcom and | 4312 | (png-mng-implement) of this and library builders who use Openwatcom and |
4313 | therefore set PNG_API_RULE to 2 should also contact the mailing list. | 4313 | therefore set PNG_API_RULE to 2 should also contact the mailing list. |
4314 | 4314 | ||
4315 | A new test program, pngvalid, is provided in addition to pngtest. | 4315 | A new test program, pngvalid, is provided in addition to pngtest. |
4316 | pngvalid validates the arithmetic accuracy of the gamma correction | 4316 | pngvalid validates the arithmetic accuracy of the gamma correction |
4317 | calculations and includes a number of validations of the file format. | 4317 | calculations and includes a number of validations of the file format. |
4318 | A subset of the full range of tests is run when "make check" is done | 4318 | A subset of the full range of tests is run when "make check" is done |
4319 | (in the 'configure' build.) pngvalid also allows total allocated memory | 4319 | (in the 'configure' build.) pngvalid also allows total allocated memory |
4320 | usage to be evaluated and performs additional memory overwrite validation. | 4320 | usage to be evaluated and performs additional memory overwrite validation. |
4321 | 4321 | ||
4322 | Many changes to individual feature macros have been made. The following | 4322 | Many changes to individual feature macros have been made. The following |
4323 | are the changes most likely to be noticed by library builders who | 4323 | are the changes most likely to be noticed by library builders who |
4324 | configure libpng: | 4324 | configure libpng: |
4325 | 4325 | ||
4326 | 1) All feature macros now have consistent naming: | 4326 | 1) All feature macros now have consistent naming: |
4327 | 4327 | ||
4328 | #define PNG_NO_feature turns the feature off | 4328 | #define PNG_NO_feature turns the feature off |
4329 | #define PNG_feature_SUPPORTED turns the feature on | 4329 | #define PNG_feature_SUPPORTED turns the feature on |
4330 | 4330 | ||
4331 | pnglibconf.h contains one line for each feature macro which is either: | 4331 | pnglibconf.h contains one line for each feature macro which is either: |
4332 | 4332 | ||
4333 | #define PNG_feature_SUPPORTED | 4333 | #define PNG_feature_SUPPORTED |
4334 | 4334 | ||
4335 | if the feature is supported or: | 4335 | if the feature is supported or: |
4336 | 4336 | ||
4337 | /*#undef PNG_feature_SUPPORTED*/ | 4337 | /*#undef PNG_feature_SUPPORTED*/ |
4338 | 4338 | ||
4339 | if it is not. Library code consistently checks for the 'SUPPORTED' macro. | 4339 | if it is not. Library code consistently checks for the 'SUPPORTED' macro. |
4340 | It does not, and libpng applications should not, check for the 'NO' macro | 4340 | It does not, and libpng applications should not, check for the 'NO' macro |
4341 | which will not normally be defined even if the feature is not supported. | 4341 | which will not normally be defined even if the feature is not supported. |
4342 | The 'NO' macros are only used internally for setting or not setting the | 4342 | The 'NO' macros are only used internally for setting or not setting the |
4343 | corresponding 'SUPPORTED' macros. | 4343 | corresponding 'SUPPORTED' macros. |
4344 | 4344 | ||
4345 | Compatibility with the old names is provided as follows: | 4345 | Compatibility with the old names is provided as follows: |
4346 | 4346 | ||
4347 | PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED | 4347 | PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED |
4348 | 4348 | ||
4349 | And the following definitions disable the corresponding feature: | 4349 | And the following definitions disable the corresponding feature: |
4350 | 4350 | ||
4351 | PNG_SETJMP_NOT_SUPPORTED disables SETJMP | 4351 | PNG_SETJMP_NOT_SUPPORTED disables SETJMP |
4352 | PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS | 4352 | PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS |
4353 | PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV | 4353 | PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV |
4354 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS | 4354 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS |
4355 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS | 4355 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS |
4356 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS | 4356 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS |
4357 | 4357 | ||
4358 | Library builders should remove use of the above, inconsistent, names. | 4358 | Library builders should remove use of the above, inconsistent, names. |
4359 | 4359 | ||
4360 | 2) Warning and error message formatting was previously conditional on | 4360 | 2) Warning and error message formatting was previously conditional on |
4361 | the STDIO feature. The library has been changed to use the | 4361 | the STDIO feature. The library has been changed to use the |
4362 | CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled | 4362 | CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled |
4363 | the library no longer uses the printf(3) functions, even though the | 4363 | the library no longer uses the printf(3) functions, even though the |
4364 | default read/write implementations use (FILE) style stdio.h functions. | 4364 | default read/write implementations use (FILE) style stdio.h functions. |
4365 | 4365 | ||
4366 | 3) Three feature macros now control the fixed/floating point decisions: | 4366 | 3) Three feature macros now control the fixed/floating point decisions: |
4367 | 4367 | ||
4368 | PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs | 4368 | PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs |
4369 | 4369 | ||
4370 | PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in | 4370 | PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in |
4371 | practice these are normally required internally anyway (because the PNG | 4371 | practice these are normally required internally anyway (because the PNG |
4372 | file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT | 4372 | file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT |
4373 | merely stops the function from being exported. | 4373 | merely stops the function from being exported. |
4374 | 4374 | ||
4375 | PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating | 4375 | PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating |
4376 | point implementation or the fixed point one. Typically the fixed point | 4376 | point implementation or the fixed point one. Typically the fixed point |
4377 | implementation is larger and slower than the floating point implementation | 4377 | implementation is larger and slower than the floating point implementation |
4378 | on a system that supports floating point, however it may be faster on a | 4378 | on a system that supports floating point, however it may be faster on a |
4379 | system which lacks floating point hardware and therefore uses a software | 4379 | system which lacks floating point hardware and therefore uses a software |
4380 | emulation. | 4380 | emulation. |
4381 | 4381 | ||
4382 | 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the | 4382 | 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the |
4383 | functions to read and write ints to be disabled independently of | 4383 | functions to read and write ints to be disabled independently of |
4384 | PNG_USE_READ_MACROS, which allows libpng to be built with the functions | 4384 | PNG_USE_READ_MACROS, which allows libpng to be built with the functions |
4385 | even though the default is to use the macros - this allows applications | 4385 | even though the default is to use the macros - this allows applications |
4386 | to choose at app buildtime whether or not to use macros (previously | 4386 | to choose at app buildtime whether or not to use macros (previously |
4387 | impossible because the functions weren't in the default build.) | 4387 | impossible because the functions weren't in the default build.) |
4388 | 4388 | ||
4389 | B.2 Changes to the configuration mechanism | 4389 | B.2 Changes to the configuration mechanism |
4390 | 4390 | ||
4391 | Prior to libpng-1.5.0 library builders who needed to configure libpng | 4391 | Prior to libpng-1.5.0 library builders who needed to configure libpng |
4392 | had either to modify the exported pngconf.h header file to add system | 4392 | had either to modify the exported pngconf.h header file to add system |
4393 | specific configuration or had to write feature selection macros into | 4393 | specific configuration or had to write feature selection macros into |
4394 | pngusr.h and cause this to be included into pngconf.h by defining | 4394 | pngusr.h and cause this to be included into pngconf.h by defining |
4395 | PNG_USER_CONFIG. The latter mechanism had the disadvantage that an | 4395 | PNG_USER_CONFIG. The latter mechanism had the disadvantage that an |
4396 | application built without PNG_USER_CONFIG defined would see the | 4396 | application built without PNG_USER_CONFIG defined would see the |
4397 | unmodified, default, libpng API and thus would probably fail to link. | 4397 | unmodified, default, libpng API and thus would probably fail to link. |
4398 | 4398 | ||
4399 | These mechanisms still work in the configure build and in any makefile | 4399 | These mechanisms still work in the configure build and in any makefile |
4400 | build that builds pnglibconf.h, although the feature selection macros | 4400 | build that builds pnglibconf.h, although the feature selection macros |
4401 | have changed somewhat as described above. In 1.5.0, however, pngusr.h is | 4401 | have changed somewhat as described above. In 1.5.0, however, pngusr.h is |
4402 | processed only once, when the exported header file pnglibconf.h is built. | 4402 | processed only once, when the exported header file pnglibconf.h is built. |
4403 | pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the | 4403 | pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the |
4404 | build of pnglibconf.h and it is never included in an application build. | 4404 | build of pnglibconf.h and it is never included in an application build. |
4405 | 4405 | ||
4406 | The rarely used alternative of adding a list of feature macros to the | 4406 | The rarely used alternative of adding a list of feature macros to the |
4407 | CFLAGS setting in the build also still works, however the macros will be | 4407 | CFLAGS setting in the build also still works, however the macros will be |
4408 | copied to pnglibconf.h and this may produce macro redefinition warnings | 4408 | copied to pnglibconf.h and this may produce macro redefinition warnings |
4409 | when the individual C files are compiled. | 4409 | when the individual C files are compiled. |
4410 | 4410 | ||
4411 | All configuration now only works if pnglibconf.h is built from | 4411 | All configuration now only works if pnglibconf.h is built from |
4412 | scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan | 4412 | scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan |
4413 | (the original author of awk) maintains C source code of that awk and this | 4413 | (the original author of awk) maintains C source code of that awk and this |
4414 | and all known later implementations (often called by subtly different | 4414 | and all known later implementations (often called by subtly different |
4415 | names - nawk and gawk for example) are adequate to build pnglibconf.h. | 4415 | names - nawk and gawk for example) are adequate to build pnglibconf.h. |
4416 | The Sun Microsystems (now Oracle) program 'awk' is an earlier version | 4416 | The Sun Microsystems (now Oracle) program 'awk' is an earlier version |
4417 | and does not work; this may also apply to other systems that have a | 4417 | and does not work; this may also apply to other systems that have a |
4418 | functioning awk called 'nawk'. | 4418 | functioning awk called 'nawk'. |
4419 | 4419 | ||
4420 | Configuration options are now documented in scripts/pnglibconf.dfa. This | 4420 | Configuration options are now documented in scripts/pnglibconf.dfa. This |
4421 | file also includes dependency information that ensures a configuration is | 4421 | file also includes dependency information that ensures a configuration is |
4422 | consistent; that is, if a feature is switched off dependent features are | 4422 | consistent; that is, if a feature is switched off dependent features are |
4423 | also removed. As a recommended alternative to using feature macros in | 4423 | also removed. As a recommended alternative to using feature macros in |
4424 | pngusr.h a system builder may also define equivalent options in pngusr.dfa | 4424 | pngusr.h a system builder may also define equivalent options in pngusr.dfa |
4425 | (or, indeed, any file) and add that to the configuration by setting | 4425 | (or, indeed, any file) and add that to the configuration by setting |
4426 | DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate | 4426 | DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate |
4427 | how to do this, and a case where pngusr.h is still required. | 4427 | how to do this, and a case where pngusr.h is still required. |
4428 | 4428 | ||
4429 | XI. Detecting libpng | 4429 | XI. Detecting libpng |
4430 | 4430 | ||
4431 | The png_get_io_ptr() function has been present since libpng-0.88, has never | 4431 | The png_get_io_ptr() function has been present since libpng-0.88, has never |
4432 | changed, and is unaffected by conditional compilation macros. It is the | 4432 | changed, and is unaffected by conditional compilation macros. It is the |
4433 | best choice for use in configure scripts for detecting the presence of any | 4433 | best choice for use in configure scripts for detecting the presence of any |
4434 | libpng version since 0.88. In an autoconf "configure.in" you could use | 4434 | libpng version since 0.88. In an autoconf "configure.in" you could use |
4435 | 4435 | ||
4436 | AC_CHECK_LIB(png, png_get_io_ptr, ... | 4436 | AC_CHECK_LIB(png, png_get_io_ptr, ... |
4437 | 4437 | ||
4438 | XII. Source code repository | 4438 | XII. Source code repository |
4439 | 4439 | ||
4440 | Since about February 2009, version 1.2.34, libpng has been under "git" source | 4440 | Since about February 2009, version 1.2.34, libpng has been under "git" source |
4441 | control. The git repository was built from old libpng-x.y.z.tar.gz files | 4441 | control. The git repository was built from old libpng-x.y.z.tar.gz files |
4442 | going back to version 0.70. You can access the git repository (read only) | 4442 | going back to version 0.70. You can access the git repository (read only) |
4443 | at | 4443 | at |
4444 | 4444 | ||
4445 | git://libpng.git.sourceforge.net/gitroot/libpng | 4445 | git://libpng.git.sourceforge.net/gitroot/libpng |
4446 | 4446 | ||
4447 | or you can browse it via "gitweb" at | 4447 | or you can browse it via "gitweb" at |
4448 | 4448 | ||
4449 | http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng | 4449 | http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng |
4450 | 4450 | ||
4451 | Patches can be sent to glennrp at users.sourceforge.net or to | 4451 | Patches can be sent to glennrp at users.sourceforge.net or to |
4452 | png-mng-implement at lists.sourceforge.net or you can upload them to | 4452 | png-mng-implement at lists.sourceforge.net or you can upload them to |
4453 | the libpng bug tracker at | 4453 | the libpng bug tracker at |
4454 | 4454 | ||
4455 | http://libpng.sourceforge.net | 4455 | http://libpng.sourceforge.net |
4456 | 4456 | ||
4457 | We also accept patches built from the tar or zip distributions, and | 4457 | We also accept patches built from the tar or zip distributions, and |
4458 | simple verbal discriptions of bug fixes, reported either to the | 4458 | simple verbal discriptions of bug fixes, reported either to the |
4459 | SourceForge bug tracker, to the png-mng-implement at lists.sf.net | 4459 | SourceForge bug tracker, to the png-mng-implement at lists.sf.net |
4460 | mailing list, or directly to glennrp. | 4460 | mailing list, or directly to glennrp. |
4461 | 4461 | ||
4462 | XIII. Coding style | 4462 | XIII. Coding style |
4463 | 4463 | ||
4464 | Our coding style is similar to the "Allman" style, with curly | 4464 | Our coding style is similar to the "Allman" style, with curly |
4465 | braces on separate lines: | 4465 | braces on separate lines: |
4466 | 4466 | ||
4467 | if (condition) | 4467 | if (condition) |
4468 | { | 4468 | { |
4469 | action; | 4469 | action; |
4470 | } | 4470 | } |
4471 | 4471 | ||
4472 | else if (another condition) | 4472 | else if (another condition) |
4473 | { | 4473 | { |
4474 | another action; | 4474 | another action; |
4475 | } | 4475 | } |
4476 | 4476 | ||
4477 | The braces can be omitted from simple one-line actions: | 4477 | The braces can be omitted from simple one-line actions: |
4478 | 4478 | ||
4479 | if (condition) | 4479 | if (condition) |
4480 | return (0); | 4480 | return (0); |
4481 | 4481 | ||
4482 | We use 3-space indentation, except for continued statements which | 4482 | We use 3-space indentation, except for continued statements which |
4483 | are usually indented the same as the first line of the statement | 4483 | are usually indented the same as the first line of the statement |
4484 | plus four more spaces. | 4484 | plus four more spaces. |
4485 | 4485 | ||
4486 | For macro definitions we use 2-space indentation, always leaving the "#" | 4486 | For macro definitions we use 2-space indentation, always leaving the "#" |
4487 | in the first column. | 4487 | in the first column. |
4488 | 4488 | ||
4489 | #ifndef PNG_NO_FEATURE | 4489 | #ifndef PNG_NO_FEATURE |
4490 | # ifndef PNG_FEATURE_SUPPORTED | 4490 | # ifndef PNG_FEATURE_SUPPORTED |
4491 | # define PNG_FEATURE_SUPPORTED | 4491 | # define PNG_FEATURE_SUPPORTED |
4492 | # endif | 4492 | # endif |
4493 | #endif | 4493 | #endif |
4494 | 4494 | ||
4495 | Comments appear with the leading "/*" at the same indentation as | 4495 | Comments appear with the leading "/*" at the same indentation as |
4496 | the statement that follows the comment: | 4496 | the statement that follows the comment: |
4497 | 4497 | ||
4498 | /* Single-line comment */ | 4498 | /* Single-line comment */ |
4499 | statement; | 4499 | statement; |
4500 | 4500 | ||
4501 | /* This is a multiple-line | 4501 | /* This is a multiple-line |
4502 | * comment. | 4502 | * comment. |
4503 | */ | 4503 | */ |
4504 | statement; | 4504 | statement; |
4505 | 4505 | ||
4506 | Very short comments can be placed after the end of the statement | 4506 | Very short comments can be placed after the end of the statement |
4507 | to which they pertain: | 4507 | to which they pertain: |
4508 | 4508 | ||
4509 | statement; /* comment */ | 4509 | statement; /* comment */ |
4510 | 4510 | ||
4511 | We don't use C++ style ("//") comments. We have, however, | 4511 | We don't use C++ style ("//") comments. We have, however, |
4512 | used them in the past in some now-abandoned MMX assembler | 4512 | used them in the past in some now-abandoned MMX assembler |
4513 | code. | 4513 | code. |
4514 | 4514 | ||
4515 | Functions and their curly braces are not indented, and | 4515 | Functions and their curly braces are not indented, and |
4516 | exported functions are marked with PNGAPI: | 4516 | exported functions are marked with PNGAPI: |
4517 | 4517 | ||
4518 | /* This is a public function that is visible to | 4518 | /* This is a public function that is visible to |
4519 | * application programmers. It does thus-and-so. | 4519 | * application programmers. It does thus-and-so. |
4520 | */ | 4520 | */ |
4521 | void PNGAPI | 4521 | void PNGAPI |
4522 | png_exported_function(png_ptr, png_info, foo) | 4522 | png_exported_function(png_ptr, png_info, foo) |
4523 | { | 4523 | { |
4524 | body; | 4524 | body; |
4525 | } | 4525 | } |
4526 | 4526 | ||
4527 | The prototypes for all exported functions appear in png.h, | 4527 | The prototypes for all exported functions appear in png.h, |
4528 | above the comment that says | 4528 | above the comment that says |
4529 | 4529 | ||
4530 | /* Maintainer: Put new public prototypes here ... */ | 4530 | /* Maintainer: Put new public prototypes here ... */ |
4531 | 4531 | ||
4532 | We mark all non-exported functions with "/* PRIVATE */"": | 4532 | We mark all non-exported functions with "/* PRIVATE */"": |
4533 | 4533 | ||
4534 | void /* PRIVATE */ | 4534 | void /* PRIVATE */ |
4535 | png_non_exported_function(png_ptr, png_info, foo) | 4535 | png_non_exported_function(png_ptr, png_info, foo) |
4536 | { | 4536 | { |
4537 | body; | 4537 | body; |
4538 | } | 4538 | } |
4539 | 4539 | ||
4540 | The prototypes for non-exported functions (except for those in | 4540 | The prototypes for non-exported functions (except for those in |
4541 | pngtest) appear in | 4541 | pngtest) appear in |
4542 | pngpriv.h | 4542 | pngpriv.h |
4543 | above the comment that says | 4543 | above the comment that says |
4544 | 4544 | ||
4545 | /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */ | 4545 | /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */ |
4546 | 4546 | ||
4547 | To avoid polluting the global namespace, the names of all exported | 4547 | To avoid polluting the global namespace, the names of all exported |
4548 | functions and variables begin with "png_", and all publicly visible C | 4548 | functions and variables begin with "png_", and all publicly visible C |
4549 | preprocessor macros begin with "PNG_". We request that applications that | 4549 | preprocessor macros begin with "PNG_". We request that applications that |
4550 | use libpng *not* begin any of their own symbols with either of these strings. | 4550 | use libpng *not* begin any of their own symbols with either of these strings. |
4551 | 4551 | ||
4552 | We put a space after each comma and after each semicolon | 4552 | We put a space after each comma and after each semicolon |
4553 | in "for" statements, and we put spaces before and after each | 4553 | in "for" statements, and we put spaces before and after each |
4554 | C binary operator and after "for" or "while", and before | 4554 | C binary operator and after "for" or "while", and before |
4555 | "?". We don't put a space between a typecast and the expression | 4555 | "?". We don't put a space between a typecast and the expression |
4556 | being cast, nor do we put one between a function name and the | 4556 | being cast, nor do we put one between a function name and the |
4557 | left parenthesis that follows it: | 4557 | left parenthesis that follows it: |
4558 | 4558 | ||
4559 | for (i = 2; i > 0; --i) | 4559 | for (i = 2; i > 0; --i) |
4560 | y[i] = a(x) + (int)b; | 4560 | y[i] = a(x) + (int)b; |
4561 | 4561 | ||
4562 | We prefer #ifdef and #ifndef to #if defined() and if !defined() | 4562 | We prefer #ifdef and #ifndef to #if defined() and if !defined() |
4563 | when there is only one macro being tested. | 4563 | when there is only one macro being tested. |
4564 | 4564 | ||
4565 | We prefer to express integers that are used as bit masks in hex format, | 4565 | We prefer to express integers that are used as bit masks in hex format, |
4566 | with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100). | 4566 | with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100). |
4567 | 4567 | ||
4568 | We do not use the TAB character for indentation in the C sources. | 4568 | We do not use the TAB character for indentation in the C sources. |
4569 | 4569 | ||
4570 | Lines do not exceed 80 characters. | 4570 | Lines do not exceed 80 characters. |
4571 | 4571 | ||
4572 | Other rules can be inferred by inspecting the libpng source. | 4572 | Other rules can be inferred by inspecting the libpng source. |
4573 | 4573 | ||
4574 | XIV. Y2K Compliance in libpng | 4574 | XIV. Y2K Compliance in libpng |
4575 | 4575 | ||
4576 | February 18, 2012 | 4576 | February 18, 2012 |
4577 | 4577 | ||
4578 | Since the PNG Development group is an ad-hoc body, we can't make | 4578 | Since the PNG Development group is an ad-hoc body, we can't make |
4579 | an official declaration. | 4579 | an official declaration. |
4580 | 4580 | ||
4581 | This is your unofficial assurance that libpng from version 0.71 and | 4581 | This is your unofficial assurance that libpng from version 0.71 and |
4582 | upward through 1.5.9 are Y2K compliant. It is my belief that earlier | 4582 | upward through 1.5.9 are Y2K compliant. It is my belief that earlier |
4583 | versions were also Y2K compliant. | 4583 | versions were also Y2K compliant. |
4584 | 4584 | ||
4585 | Libpng only has three year fields. One is a 2-byte unsigned integer that | 4585 | Libpng only has three year fields. One is a 2-byte unsigned integer that |
4586 | will hold years up to 65535. The other two hold the date in text | 4586 | will hold years up to 65535. The other two hold the date in text |
4587 | format, and will hold years up to 9999. | 4587 | format, and will hold years up to 9999. |
4588 | 4588 | ||
4589 | The integer is | 4589 | The integer is |
4590 | "png_uint_16 year" in png_time_struct. | 4590 | "png_uint_16 year" in png_time_struct. |
4591 | 4591 | ||
4592 | The strings are | 4592 | The strings are |
4593 | "png_charp time_buffer" in png_struct and | 4593 | "png_charp time_buffer" in png_struct and |
4594 | "near_time_buffer", which is a local character string in png.c. | 4594 | "near_time_buffer", which is a local character string in png.c. |
4595 | 4595 | ||
4596 | There are seven time-related functions: | 4596 | There are seven time-related functions: |
4597 | 4597 | ||
4598 | png_convert_to_rfc_1123() in png.c | 4598 | png_convert_to_rfc_1123() in png.c |
4599 | (formerly png_convert_to_rfc_1152() in error) | 4599 | (formerly png_convert_to_rfc_1152() in error) |
4600 | png_convert_from_struct_tm() in pngwrite.c, called | 4600 | png_convert_from_struct_tm() in pngwrite.c, called |
4601 | in pngwrite.c | 4601 | in pngwrite.c |
4602 | png_convert_from_time_t() in pngwrite.c | 4602 | png_convert_from_time_t() in pngwrite.c |
4603 | png_get_tIME() in pngget.c | 4603 | png_get_tIME() in pngget.c |
4604 | png_handle_tIME() in pngrutil.c, called in pngread.c | 4604 | png_handle_tIME() in pngrutil.c, called in pngread.c |
4605 | png_set_tIME() in pngset.c | 4605 | png_set_tIME() in pngset.c |
4606 | png_write_tIME() in pngwutil.c, called in pngwrite.c | 4606 | png_write_tIME() in pngwutil.c, called in pngwrite.c |
4607 | 4607 | ||
4608 | All appear to handle dates properly in a Y2K environment. The | 4608 | All appear to handle dates properly in a Y2K environment. The |
4609 | png_convert_from_time_t() function calls gmtime() to convert from system | 4609 | png_convert_from_time_t() function calls gmtime() to convert from system |
4610 | clock time, which returns (year - 1900), which we properly convert to | 4610 | clock time, which returns (year - 1900), which we properly convert to |
4611 | the full 4-digit year. There is a possibility that applications using | 4611 | the full 4-digit year. There is a possibility that applications using |
4612 | libpng are not passing 4-digit years into the png_convert_to_rfc_1123() | 4612 | libpng are not passing 4-digit years into the png_convert_to_rfc_1123() |
4613 | function, or that they are incorrectly passing only a 2-digit year | 4613 | function, or that they are incorrectly passing only a 2-digit year |
4614 | instead of "year - 1900" into the png_convert_from_struct_tm() function, | 4614 | instead of "year - 1900" into the png_convert_from_struct_tm() function, |
4615 | but this is not under our control. The libpng documentation has always | 4615 | but this is not under our control. The libpng documentation has always |
4616 | stated that it works with 4-digit years, and the APIs have been | 4616 | stated that it works with 4-digit years, and the APIs have been |
4617 | documented as such. | 4617 | documented as such. |
4618 | 4618 | ||
4619 | The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned | 4619 | The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned |
4620 | integer to hold the year, and can hold years as large as 65535. | 4620 | integer to hold the year, and can hold years as large as 65535. |
4621 | 4621 | ||
4622 | zlib, upon which libpng depends, is also Y2K compliant. It contains | 4622 | zlib, upon which libpng depends, is also Y2K compliant. It contains |
4623 | no date-related code. | 4623 | no date-related code. |
4624 | 4624 | ||
4625 | 4625 | ||
4626 | Glenn Randers-Pehrson | 4626 | Glenn Randers-Pehrson |
4627 | libpng maintainer | 4627 | libpng maintainer |
4628 | PNG Development Group | 4628 | PNG Development Group |