Tutorial 3.CustomSceneNode

This Tutorial is a tutorial for more advanced developers. If you are currently just playing around with the Irrlicht engine, please look at other examples first. This tutorial shows how to create a custom scene node and how to use it in the engine. A custom scene node is needed, if you want to implement a render technique, the Irrlicht Engine is currently not supporting. For example you can write a indoor portal based renderer or a advanced terrain scene node with it. With creating custom scene nodes, you can easily extend the Irrlicht Engine and adapt it to your needs.

I will keep the tutorial simple: Keep everything very short, everything in one .cpp file, and I'll use the engine here as in all other tutorials. At the end of the tutorial, the result will look like the image below. This looks not very exciting, but it is a complete customized scene node and a good point to start from creating you own scene nodes.

Lets start!

To start, I include the header files, use the irr namespace, and tell the linker to link with the .lib file. 

#include <irrlicht.h>
using namespace irr;
#pragma comment(lib, "Irrlicht.lib")

Here comes the most sophisticated part of this tutorial: The class of our very own custom scene node. To keep it simple,
our scene node will not be an indoor portal renderer nor a terrain scene node, but a simple tetraeder, a 3d object consiting of 4 connected vertices, which only draws itself and does nothing more.

To let our scene node be able to be inserted into the Irrlicht Engine scene, the class we create needs only be derived from the ISceneNode class and has to override some methods.

class CSampleSceneNode : public scene::ISceneNode
{

First, we declare some member variables, to hold data for our tetraeder: The bounding box, 4 vertices, and
the material of the tetraeder.

core::aabbox3d<f32> Box;
video::S3DVertex Vertices[4];
video::SMaterial Material;

The parameters of the constructor specify the parent of the scene node, a pointer to the scene manager, and an id of the scene node. In the constructor itself, we call the parent classes constructor, set some properties of the material we use to draw the scene node and create the 4 vertices of the tetraeder we will draw later. 

public:
CSampleSceneNode(scene::ISceneNode* parent, scene::ISceneManager* mgr, s32 id)
 : scene::ISceneNode(parent, mgr, id)
{ 
  Material.Wireframe = false;
  Material.Lighting = false;
  Vertices[0] = video::S3DVertex(0,0,10, 1,1,0,video::SColor(255,0,255,255),0,1);
  Vertices[1] = video::S3DVertex(10,0,-10, 1,0,0,video::SColor(255,255,0,255),1,1); 
  Vertices[2] = video::S3DVertex(0,20,0, 0,1,1,video::SColor(255,255,255,0),1,0);
  Vertices[3] = video::S3DVertex(-10,0,-10, 0,0,1,video::SColor(255,0,255,0),0,0);

The Irrlicht Engine needs to know the bounding box of your scene node. It will use it for doing automatic culling and other things. Hence we need to create a bounding box from the 4 vertices we use. If you do not want the engine to use the box for automatic culling, and/or don't want to create the box, you could also write
AutomaticCullingEnabled = false;.

  Box.reset(Vertices[0].Pos);
 		for (s32 i=1; i<4; ++i)
 			Box.addInternalPoint(Vertices[i].Pos);
}

Before it is drawn, the OnPreRender() method of every scene node in the scene is called by the scene manager. If the scene node wishes to draw itself, it may register itself in the scene manager to be drawn. This is necessary to tell the scene manager when it should call the ::render method. For example normal scene nodes render their content one after another, while stencil buffer shadows would like to be drawn after all other scene nodes. And camera or light scene nodes need to be rendered before all other scene nodes (if at all).
So here we simply register the scene node to get rendered normally. If we would like to let it be rendered like cameras or light, we would have to call SceneManager->registerNodeForRendering(this, SNRT_LIGHT_AND_CAMERA);
After this, we call the OnPreRender-method of the base class ISceneNode, which simply lets also all the child scene nodes of this node register themselves. 

virtual void OnPreRender()
{
  if (IsVisible)
    SceneManager->registerNodeForRendering(this);

  ISceneNode::OnPreRender();
}

In the render() method most of the interresting stuff happenes: The Scene node renders itself. We override this method and draw the tetraeder.

virtual void render()
{
  u16 indices[] = { 0,2,3, 2,1,3, 1,0,3, 2,0,1 };
  video::IVideoDriver* driver = SceneManager->getVideoDriver();
  driver->setMaterial(Material);
  driver->setTransform(video::ETS_WORLD, AbsoluteTransformation);
  driver->drawIndexedTriangleList(&Vertices[0], 4, &indices[0], 4);
}

At least, we create three small additional methods. GetBoundingBox() returns the bounding box of this scene node,
GetMaterialCount() returns the amount of materials in this scene node (our tetraeder only has one material), and getMaterial() returns the material at an index. Because we have only one material here, we can return the only one material, assuming that no one ever calls getMaterial() with an index greater than 0. 

  virtual const core::aabbox3d<f32>& getBoundingBox() const
  {
    return Box;
  }
  virtual u32 getMaterialCount()
  {
    return 1;
  }
  virtual video::SMaterial& getMaterial(u32 i)
  {
    return Material;
  } 
};

That's it. The Scene node is done. Now we simply have to start the engine, create the scene node and a camera, and look at the result.

int main()
{
  IrrlichtDevice *device =
       createDevice(video::EDT_OPENGL, core::dimension2d<s32>(640, 480), 16, false);
  device->setWindowCaption(L"Custom Scene Node - Irrlicht Engine Demo");
  video::IVideoDriver* driver = device->getVideoDriver();
           scene::ISceneManager* smgr = device->getSceneManager();
  smgr->addCameraSceneNode(0, core::vector3df(0,-40,0), core::vector3df(0,0,0));

Create our scene node. Note that it is dropped (->drop()) instantly after we create it. This is possible because the scene manager now takes care of it. This is not nessecary, it would also be possible to drop it at the end of the program.

CSampleSceneNode *myNode = 
  new CSampleSceneNode(smgr->getRootSceneNode(), smgr, 666);

myNode->drop();

To animate something in this boring scene consisting only of one tetraeder, and to show, that you now can use your scene node like any other scene node in the engine, we add an animator to the scene node, which rotates the node a little bit. 

scene::ISceneNodeAnimator* anim = 
   smgr->createRotationAnimator(core::vector3df(0.8f, 0, 0.8f));

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

Now draw everything and finish.

  while(device->run())
  {
    driver->beginScene(true, true, video::SColor(0,100,100,100));

    smgr->drawAll();

    driver->endScene();
  }

device->drop();
return 0;
}

That's it. Compile and play around with the program.