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_SOFTWARE2;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);

		selector->drop();

	}

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));


	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.