Irrlicht Engine Tutorial

Tutorial 7. Collision detection - and response

In this tutorial, I will show how to collision detection with the Irrlicht - Engine. I will describe 3 methods: Automatic collision detection for - moving through 3d worlds with stair climbing and sliding, manual triangle - picking and manual scene node picking.

The program which is described here will look like this:

To start, we take the program from tutorial 2, which loaded and displayed - a quake 3 level. We will use the level to walk in it and to pick triangles - from it. In addition we'll place 3 animated models into it for scene - node picking. The following code starts up the engine and loads a - quake 3 level. I will not explain it, because it should already be - known from tutorial 2.

- - - - -

#include <irrlicht.h>
-#include <iostream>

-using namespace irr;
-
-#pragma comment(lib, "Irrlicht.lib")
-
-int main()
-{
-  // let user select driver type
-
  video::E_DRIVER_TYPE driverType;

  printf("Please select the driver you want for this example:\n"\
    " (a) Direct3D 9.0c\n (b) Direct3D 8.1\n (c) OpenGL 1.5\n"\
    " (d) Software Renderer\n (e) Apfelbaum Software Renderer\n"\
    " (f) NullDevice\n (otherKey) exit\n\n");

  char i;
  std::cin >> i;

  switch(i)
  {
  case 'a': driverType = video::EDT_DIRECT3D9;break;
  case 'b': driverType = video::EDT_DIRECT3D8;break;
  case 'c': driverType = video::EDT_OPENGL;   break;
  case 'd': driverType = video::EDT_SOFTWARE; break;
  case 'e': driverType = video::EDT_BURNINGSVIDEO;break;  
  case 'f': driverType = video::EDT_NULL;     break;
  default: return 0;
  }	

-  // create device

  IrrlichtDevice *device = createDevice(driverType,
-     core::dimension2d<s32>(640, 480), 16, false);

-  if (device == 0)
    return 1; // could not create selected driver.

  video::IVideoDriver* driver = device->getVideoDriver();
  scene::ISceneManager* smgr = device->getSceneManager();

  device->getFileSystem()->addZipFileArchive
      ("../../media/map-20kdm2.pk3");
-
-	
-	scene::IAnimatedMesh* q3levelmesh = smgr->getMesh("20kdm2.bsp");
-	scene::ISceneNode* q3node = 0;
-	
-	if (q3levelmesh)
-		q3node = smgr->addOctTreeSceneNode(q3levelmesh->getMesh(0));
-

So far so good, we've loaded the quake 3 level like in tutorial - 2. Now, here comes something different: We create a triangle selector. - A triangle selector is a class which can fetch the triangles from - scene nodes for doing different things with them, for example collision - detection. There are different triangle selectors, and all can be - created with the ISceneManager. In this example, we create an OctTreeTriangleSelector, - which optimizes the triangle output a little bit by reducing it like - an octree. This is very useful for huge meshes like quake 3 levels.
- Afte we created the triangle selector, we attach it to the q3node. - This is not necessary, but in this way, we do not need to care for - the selector, for example dropping it after we do not need it anymore.

- - - - -

scene::ITriangleSelector* selector = 0;
-	
-	if (q3node)
-	{		
-		q3node->setPosition(core::vector3df(-1370,-130,-1400));
-
-		selector = smgr->createOctTreeTriangleSelector(
-            q3levelmesh->getMesh(0), q3node, 128);
-		q3node->setTriangleSelector(selector);
-	}

We add a first person shooter camera to the scene for being able - to move in the quake 3 level like in tutorial 2. But this, time, we - add a special animator to the camera: A Collision Response animator. - This thing modifies the scene node to which it is attached to in that - way, that it may no more move through walls and is affected by gravity. - The only thing we have to tell the animator is how the world looks - like, how big the scene node is, how gravity and so on. After the - collision response animator is attached to the camera, we do not have - to do anything more for collision detection, anything is done automaticly, - all other collision detection code below is for picking. And please - note another cool feature: The collsion response animator can be attached - also to all other scene nodes, not only to cameras. And it can be - mixed with other scene node animators. In this way, collision detection - and response in the Irrlicht
- engine is really, really easy.
- Now we'll take a closer look on the parameters of createCollisionResponseAnimator(). - The first parameter is the TriangleSelector, which specifies how the - world, against collision detection is done looks like. The second - parameter is the scene node, which is the object, which is affected - by collision detection, in our case it is the camera. The third defines - how big the object is, it is the radius of an ellipsoid. Try it out - and change the radius to smaller values, the camera will be able to - move closer to walls after this. The next parameter is the direction - and speed of gravity. You could set it to (0,0,0) to disable gravity. - And the last value is just a translation: Without this, the ellipsoid - with which collision detection is done would be around the camera, - and the camera would be in the middle of the ellipsoid. But as human - beings, we are used to have our eyes on top of the body, with which - we collide with our world, not in the middle of it. So we place the - scene node 50 units over the center of the ellipsoid with this parameter. - And that's it, collision detection works now.
-

- - - - -

	scene::ICameraSceneNode* camera = 	
		camera = smgr->addCameraSceneNodeFPS(0,100.0f,300.0f);
-	camera->setPosition(core::vector3df(-100,50,-150));
-
-	scene::ISceneNodeAnimator* anim =
    smgr->createCollisionResponseAnimator(
-		selector, camera, core::vector3df(30,50,30),
-		core::vector3df(0,-3,0),
-		core::vector3df(0,50,0));

-		selector->drop();

-	camera->addAnimator(anim);
-	anim->drop();

Because collision detection is no big deal in irrlicht, I'll describe - how to do two different types of picking in the next section. But - before this, I'll prepare the scene a little. I need three animated - characters which we
- could pick later, a dynamic light for lighting them, a billboard for - drawing where we found an intersection, and, yes, I need to get rid - of this mouse cursor. :)

- - - - -

	// disable mouse cursor
-
-	device->getCursorControl()->setVisible(false);
-
-	// add billboard
-
-	scene::IBillboardSceneNode * bill = smgr->addBillboardSceneNode();
-	bill->setMaterialType(video::EMT_TRANSPARENT_ADD_COLOR );
-	bill->setMaterialTexture(0, driver->getTexture(
         "../../media/particle.bmp"));
-	bill->setMaterialFlag(video::EMF_LIGHTING, false);
-	bill->setSize(core::dimension2d<f32>(20.0f, 20.0f));
-
-	// add 3 animated faeries.
-
-	video::SMaterial material;
-	material.Texture1 = driver->getTexture(
         "../../media/faerie2.bmp");
-	material.Lighting = true;
-
-	scene::IAnimatedMeshSceneNode* node = 0;
-	scene::IAnimatedMesh* faerie = smgr->getMesh(
        "../../media/faerie.md2");
-
-	if (faerie)
-	{
-		node = smgr->addAnimatedMeshSceneNode(faerie);
-		node->setPosition(core::vector3df(-70,0,-90));
-		node->setMD2Animation(scene::EMAT_RUN);
-		node->getMaterial(0) = material;
-
-		node = smgr->addAnimatedMeshSceneNode(faerie);
-		node->setPosition(core::vector3df(-70,0,-30));
-		node->setMD2Animation(scene::EMAT_SALUTE);
-		node->getMaterial(0) = material;
-
-		node = smgr->addAnimatedMeshSceneNode(faerie);
-		node->setPosition(core::vector3df(-70,0,-60));
-		node->setMD2Animation(scene::EMAT_JUMP);
-		node->getMaterial(0) = material;
-	}
-
-	material.Texture1 = 0;
-	material.Lighting = false;
-
-	// Add a light
-
-	smgr->addLightSceneNode(0, core::vector3df(-60,100,400),
-		video::SColorf(1.0f,1.0f,1.0f,1.0f),
-		600.0f);

For not making it to complicated, I'm doing picking inside the drawing - loop. We take two pointers for storing the current and the last selected - scene node and start the loop.

- - - - -

	scene::ISceneNode* selectedSceneNode = 0;
-	scene::ISceneNode* lastSelectedSceneNode = 0;
-
-	
-	int lastFPS = -1;
-
-	while(device->run())
  if (device->isWindowActive())
-	{
-		driver->beginScene(true, true, 0);
-
-		smgr->drawAll();

After we've drawn the whole scene whit smgr->drawAll(), we'll do - the first picking: We want to know which triangle of the world we are - looking at. In addition, we want the exact point of the quake 3 level - we are looking at. For this, we create a 3d line starting at the position - of the camera and going through the lookAt-target of it. Then we ask - the collision manager if this line collides with a triangle of the world - stored in the triangle selector. If yes, we draw the 3d triangle and - set the position of the billboard to the intersection point.

- - - - -

		core::line3d<f32> line;
-		line.start = camera->getPosition();
-		line.end = line.start +
-         (camera->getTarget() - line.start).normalize() * 1000.0f;
-
-		core::vector3df intersection;
-		core::triangle3df tri;
-
-		if (smgr->getSceneCollisionManager()->getCollisionPoint(
-			line, selector, intersection, tri))
-		{
-			bill->setPosition(intersection);
-				
-			driver->setTransform(video::ETS_WORLD, core::matrix4());
-			driver->setMaterial(material);
-			driver->draw3DTriangle(tri, video::SColor(0,255,0,0));
-		}

Another type of picking supported by the Irrlicht Engine is scene - node picking based on bouding boxes. Every scene node has got a bounding - box, and because of that, it's very fast for example to get the scene - node which the camera looks
- at. Again, we ask the collision manager for this, and if we've got a - scene node, we highlight it by disabling Lighting in its material, if - it is not the billboard or the quake 3 level.

- - - - -

		selectedSceneNode = smgr->getSceneCollisionManager()->
-          getSceneNodeFromCameraBB(camera);
-
-		if (lastSelectedSceneNode)
-			lastSelectedSceneNode->setMaterialFlag(
-                video::EMF_LIGHTING, true);
-
-		if (selectedSceneNode == q3node ||
-           selectedSceneNode == bill)
-			selectedSceneNode = 0;
-
-		if (selectedSceneNode)
-			selectedSceneNode->setMaterialFlag(
-               video::EMF_LIGHTING, false);
-
-		lastSelectedSceneNode = selectedSceneNode;

That's it, we just have to finish drawing.

- - - - -

		driver->endScene();
-
-		int fps = driver->getFPS();
-
-		if (lastFPS != fps)
-		{
-		  core::stringw str = L"Collision detection example - Irrlicht Engine [";
		  str += driver->getName();
		  str += "] FPS:";
		  str += fps;

		  device->setWindowCaption(str.c_str());
		  lastFPS = fps;
		}
-	}
-
-	device->drop();
-	
-	return 0;
-}
-
-

Tutorial 7. Collision detection + and response

In this tutorial, I will show how to collision detection with the Irrlicht + Engine. I will describe 3 methods: Automatic collision detection for + moving through 3d worlds with stair climbing and sliding, manual triangle + picking and manual scene node picking.

The program which is described here will look like this:

To start, we take the program from tutorial 2, which loaded and displayed + a quake 3 level. We will use the level to walk in it and to pick triangles + from it. In addition we'll place 3 animated models into it for scene + node picking. The following code starts up the engine and loads a + quake 3 level. I will not explain it, because it should already be + known from tutorial 2.

+ + + + +

#include <irrlicht.h>
+#include <iostream>

+using namespace irr;
+
+#pragma comment(lib, "Irrlicht.lib")
+
+int main()
+{
+  // let user select driver type
+
  video::E_DRIVER_TYPE driverType;

  printf("Please select the driver you want for this example:\n"\
    " (a) Direct3D 9.0c\n (b) Direct3D 8.1\n (c) OpenGL 1.5\n"\
    " (d) Software Renderer\n (e) Apfelbaum Software Renderer\n"\
    " (f) NullDevice\n (otherKey) exit\n\n");

  char i;
  std::cin >> i;

  switch(i)
  {
  case 'a': driverType = video::EDT_DIRECT3D9;break;
  case 'b': driverType = video::EDT_DIRECT3D8;break;
  case 'c': driverType = video::EDT_OPENGL;   break;
  case 'd': driverType = video::EDT_SOFTWARE; break;
  case 'e': driverType = video::EDT_BURNINGSVIDEO;break;  
  case 'f': driverType = video::EDT_NULL;     break;
  default: return 0;
  }	

+  // create device

  IrrlichtDevice *device = createDevice(driverType,
+     core::dimension2d<s32>(640, 480), 16, false);

+  if (device == 0)
    return 1; // could not create selected driver.

  video::IVideoDriver* driver = device->getVideoDriver();
  scene::ISceneManager* smgr = device->getSceneManager();

  device->getFileSystem()->addZipFileArchive
      ("../../media/map-20kdm2.pk3");
+
+	
+	scene::IAnimatedMesh* q3levelmesh = smgr->getMesh("20kdm2.bsp");
+	scene::ISceneNode* q3node = 0;
+	
+	if (q3levelmesh)
+		q3node = smgr->addOctTreeSceneNode(q3levelmesh->getMesh(0));
+

So far so good, we've loaded the quake 3 level like in tutorial + 2. Now, here comes something different: We create a triangle selector. + A triangle selector is a class which can fetch the triangles from + scene nodes for doing different things with them, for example collision + detection. There are different triangle selectors, and all can be + created with the ISceneManager. In this example, we create an OctTreeTriangleSelector, + which optimizes the triangle output a little bit by reducing it like + an octree. This is very useful for huge meshes like quake 3 levels.
+ Afte we created the triangle selector, we attach it to the q3node. + This is not necessary, but in this way, we do not need to care for + the selector, for example dropping it after we do not need it anymore.

+ + + + +

scene::ITriangleSelector* selector = 0;
+	
+	if (q3node)
+	{		
+		q3node->setPosition(core::vector3df(-1370,-130,-1400));
+
+		selector = smgr->createOctTreeTriangleSelector(
+            q3levelmesh->getMesh(0), q3node, 128);
+		q3node->setTriangleSelector(selector);
+	}

We add a first person shooter camera to the scene for being able + to move in the quake 3 level like in tutorial 2. But this, time, we + add a special animator to the camera: A Collision Response animator. + This thing modifies the scene node to which it is attached to in that + way, that it may no more move through walls and is affected by gravity. + The only thing we have to tell the animator is how the world looks + like, how big the scene node is, how gravity and so on. After the + collision response animator is attached to the camera, we do not have + to do anything more for collision detection, anything is done automaticly, + all other collision detection code below is for picking. And please + note another cool feature: The collsion response animator can be attached + also to all other scene nodes, not only to cameras. And it can be + mixed with other scene node animators. In this way, collision detection + and response in the Irrlicht
+ engine is really, really easy.
+ Now we'll take a closer look on the parameters of createCollisionResponseAnimator(). + The first parameter is the TriangleSelector, which specifies how the + world, against collision detection is done looks like. The second + parameter is the scene node, which is the object, which is affected + by collision detection, in our case it is the camera. The third defines + how big the object is, it is the radius of an ellipsoid. Try it out + and change the radius to smaller values, the camera will be able to + move closer to walls after this. The next parameter is the direction + and speed of gravity. You could set it to (0,0,0) to disable gravity. + And the last value is just a translation: Without this, the ellipsoid + with which collision detection is done would be around the camera, + and the camera would be in the middle of the ellipsoid. But as human + beings, we are used to have our eyes on top of the body, with which + we collide with our world, not in the middle of it. So we place the + scene node 50 units over the center of the ellipsoid with this parameter. + And that's it, collision detection works now.
+

+ + + + +

	scene::ICameraSceneNode* camera = 	
		camera = smgr->addCameraSceneNodeFPS(0,100.0f,300.0f);
+	camera->setPosition(core::vector3df(-100,50,-150));
+
+	scene::ISceneNodeAnimator* anim =
    smgr->createCollisionResponseAnimator(
+		selector, camera, core::vector3df(30,50,30),
+		core::vector3df(0,-3,0),
+		core::vector3df(0,50,0));

+		selector->drop();

+	camera->addAnimator(anim);
+	anim->drop();

Because collision detection is no big deal in irrlicht, I'll describe + how to do two different types of picking in the next section. But + before this, I'll prepare the scene a little. I need three animated + characters which we
+ could pick later, a dynamic light for lighting them, a billboard for + drawing where we found an intersection, and, yes, I need to get rid + of this mouse cursor. :)

+ + + + +

	// disable mouse cursor
+
+	device->getCursorControl()->setVisible(false);
+
+	// add billboard
+
+	scene::IBillboardSceneNode * bill = smgr->addBillboardSceneNode();
+	bill->setMaterialType(video::EMT_TRANSPARENT_ADD_COLOR );
+	bill->setMaterialTexture(0, driver->getTexture(
         "../../media/particle.bmp"));
+	bill->setMaterialFlag(video::EMF_LIGHTING, false);
+	bill->setSize(core::dimension2d<f32>(20.0f, 20.0f));
+
+	// add 3 animated faeries.
+
+	video::SMaterial material;
+	material.Texture1 = driver->getTexture(
         "../../media/faerie2.bmp");
+	material.Lighting = true;
+
+	scene::IAnimatedMeshSceneNode* node = 0;
+	scene::IAnimatedMesh* faerie = smgr->getMesh(
        "../../media/faerie.md2");
+
+	if (faerie)
+	{
+		node = smgr->addAnimatedMeshSceneNode(faerie);
+		node->setPosition(core::vector3df(-70,0,-90));
+		node->setMD2Animation(scene::EMAT_RUN);
+		node->getMaterial(0) = material;
+
+		node = smgr->addAnimatedMeshSceneNode(faerie);
+		node->setPosition(core::vector3df(-70,0,-30));
+		node->setMD2Animation(scene::EMAT_SALUTE);
+		node->getMaterial(0) = material;
+
+		node = smgr->addAnimatedMeshSceneNode(faerie);
+		node->setPosition(core::vector3df(-70,0,-60));
+		node->setMD2Animation(scene::EMAT_JUMP);
+		node->getMaterial(0) = material;
+	}
+
+	material.Texture1 = 0;
+	material.Lighting = false;
+
+	// Add a light
+
+	smgr->addLightSceneNode(0, core::vector3df(-60,100,400),
+		video::SColorf(1.0f,1.0f,1.0f,1.0f),
+		600.0f);

For not making it to complicated, I'm doing picking inside the drawing + loop. We take two pointers for storing the current and the last selected + scene node and start the loop.

+ + + + +

	scene::ISceneNode* selectedSceneNode = 0;
+	scene::ISceneNode* lastSelectedSceneNode = 0;
+
+	
+	int lastFPS = -1;
+
+	while(device->run())
  if (device->isWindowActive())
+	{
+		driver->beginScene(true, true, 0);
+
+		smgr->drawAll();

After we've drawn the whole scene whit smgr->drawAll(), we'll do + the first picking: We want to know which triangle of the world we are + looking at. In addition, we want the exact point of the quake 3 level + we are looking at. For this, we create a 3d line starting at the position + of the camera and going through the lookAt-target of it. Then we ask + the collision manager if this line collides with a triangle of the world + stored in the triangle selector. If yes, we draw the 3d triangle and + set the position of the billboard to the intersection point.

+ + + + +

		core::line3d<f32> line;
+		line.start = camera->getPosition();
+		line.end = line.start +
+         (camera->getTarget() - line.start).normalize() * 1000.0f;
+
+		core::vector3df intersection;
+		core::triangle3df tri;
+
+		if (smgr->getSceneCollisionManager()->getCollisionPoint(
+			line, selector, intersection, tri))
+		{
+			bill->setPosition(intersection);
+				
+			driver->setTransform(video::ETS_WORLD, core::matrix4());
+			driver->setMaterial(material);
+			driver->draw3DTriangle(tri, video::SColor(0,255,0,0));
+		}

Another type of picking supported by the Irrlicht Engine is scene + node picking based on bouding boxes. Every scene node has got a bounding + box, and because of that, it's very fast for example to get the scene + node which the camera looks
+ at. Again, we ask the collision manager for this, and if we've got a + scene node, we highlight it by disabling Lighting in its material, if + it is not the billboard or the quake 3 level.

+ + + + +

		selectedSceneNode = smgr->getSceneCollisionManager()->
+          getSceneNodeFromCameraBB(camera);
+
+		if (lastSelectedSceneNode)
+			lastSelectedSceneNode->setMaterialFlag(
+                video::EMF_LIGHTING, true);
+
+		if (selectedSceneNode == q3node ||
+           selectedSceneNode == bill)
+			selectedSceneNode = 0;
+
+		if (selectedSceneNode)
+			selectedSceneNode->setMaterialFlag(
+               video::EMF_LIGHTING, false);
+
+		lastSelectedSceneNode = selectedSceneNode;

That's it, we just have to finish drawing.

+ + + + +

		driver->endScene();
+
+		int fps = driver->getFPS();
+
+		if (lastFPS != fps)
+		{
+		  core::stringw str = L"Collision detection example - Irrlicht Engine [";
		  str += driver->getName();
		  str += "] FPS:";
		  str += fps;

		  device->setWindowCaption(str.c_str());
		  lastFPS = fps;
		}
+	}
+
+	device->drop();
+	
+	return 0;
+}
+
+

	- - - Tutorial 7. Collision detection - and response - -
- - In this tutorial, I will show how to collision detection with the Irrlicht - Engine. I will describe 3 methods: Automatic collision detection for - moving through 3d worlds with stair climbing and sliding, manual triangle - picking and manual scene node picking. - The program which is described here will look like this: - - - -

	+ + + Tutorial 7. Collision detection + and response + +
+ + In this tutorial, I will show how to collision detection with the Irrlicht + Engine. I will describe 3 methods: Automatic collision detection for + moving through 3d worlds with stair climbing and sliding, manual triangle + picking and manual scene node picking. + The program which is described here will look like this: + + + +