| Tutorial 13. Render to Texture
This tutorial shows how to render to a texture using Irrlicht. Render to texture is a feature with which it is possible to create nice special effects. In addition, this tutorial shows how to enable specular highlights. The program which is described here will look like this:

Lets start!

In the beginning, everything as usual. Include the needed headers, ask the user for the rendering driver, create the Irrlicht Device:

    #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 = video::EDT_DIRECT3D9;

    	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 1;
    	}

    	// create device and exit if creation failed

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

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

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

Now, we load an animated mesh to be displayed. As in most examples, we'll take the fairy md2 model. The difference here: We set the shininess
of the model to a value other than 0 which is the default value. This enables specular highlights on the model if dynamic lighting is on. The value influences the size of the highlights.

    // load and display animated fairy mesh

    	scene::IAnimatedMeshSceneNode* fairy = smgr->addAnimatedMeshSceneNode(
    		smgr->getMesh("../../media/faerie.md2"));

    	if (fairy)
    	{
    		fairy->setMaterialTexture(0, driver->getTexture("../../media/faerie2.bmp")); // set diffuse texture
    		fairy->setMaterialFlag(video::EMF_LIGHTING, true); // enable dynamic lighting
    		fairy->getMaterial(0).Shininess = 20.0f; // set size of specular highlights
    		fairy->setPosition(core::vector3df(-10,0,-100));
    	}

To make specular highlights appear on the model, we need a dynamic light in the scene. We add one directly in vicinity of the model. In addition, to make the model not that dark, we set the ambient light to gray.

    	// add white light
    	scene::ILightSceneNode* light = smgr->addLightSceneNode(0,
    		core::vector3df(-15,5,-105), video::SColorf(1.0f, 1.0f, 1.0f));

    	// set ambient light
    	driver->setAmbientLight(video::SColor(0,60,60,60));

The next is just some standard stuff: Add a user controlled camera to the scene, disable mouse cursor, and add a test cube and let it rotate to make the scene more interesting.

    	// add fps camera
    	scene::ICameraSceneNode* fpsCamera = smgr->addCameraSceneNodeFPS();
    	fpsCamera->setPosition(core::vector3df(-50,50,-150));

    	// disable mouse cursor
    	device->getCursorControl()->setVisible(false);

    	// create test cube
    	scene::ISceneNode* test = smgr->addCubeSceneNode(60);

    	// let the cube rotate and set some light settings
    	scene::ISceneNodeAnimator* anim = smgr->createRotationAnimator(
    		core::vector3df(0.3f, 0.3f,0));

    	test->setPosition(core::vector3df(-100,0,-100));
    	test->setMaterialFlag(video::EMF_LIGHTING, false); // disable dynamic lighting
    	test->addAnimator(anim);
    	anim->drop();

    	// set window caption
    	device->setWindowCaption(L"Irrlicht Engine - Render to Texture and Specular Highlights example");

To test out the render to texture feature, we need a render target texture. These are not like standard textures, but need to be created first. To create one, we call IVideoDriver::createRenderTargetTexture() and specify the size of the texture. Please don't use sizes bigger than the frame buffer for this, because the render target shares the zbuffer with the frame buffer. And because we want to render the scene not from the user camera into the texture, we add another, fixed camera to the scene. But before we do all this, we check if the current running driver is able to render to textures. If it is not, we simply display a warning text.

    // create render target
    	video::ITexture* rt = 0;
    	scene::ICameraSceneNode* fixedCam = 0;

    	if (driver->queryFeature(video::EVDF_RENDER_TO_TARGET))
    	{
    		rt = driver->createRenderTargetTexture(core::dimension2d<s32>(256,256));
    		test->setMaterialTexture(0, rt); // set material of cube to render target

    		// add fixed camera
    		fixedCam = smgr->addCameraSceneNode(0, core::vector3df(10,10,-80),
    			core::vector3df(-10,10,-100));
    	}
    	else
    	{
    		// create problem text
    		gui::IGUISkin* skin = env->getSkin();
    		gui::IGUIFont* font = env->getFont("../../media/fonthaettenschweiler.bmp");
    		if (font)
    			skin->setFont(font);

    		gui::IGUIStaticText* text = env->addStaticText(
    			L"Your hardware or this renderer is not able to use the "\
    			L"render to texture feature. RTT Disabled.",
    			core::rect<s32>(150,20,470,60));

    		text->setOverrideColor(video::SColor(100,255,255,255));
    	}

Nearly finished. Now we need to draw everything. Every frame, we draw the scene twice. Once from the fixed camera into the render target texture and once as usual. When rendering into the render target, we need to disable the visibilty of the test cube, because it has the render target texture applied to it.
That's, wasn't quite complicated I hope. :)

    while(device->run())
    	if (device->isWindowActive())
    	{
    		driver->beginScene(true, true, 0);

    		if (rt)
    		{
    			// draw scene into render target

    			// set render target texture
    			driver->setRenderTarget(rt, true, true, video::SColor(0,0,0,255));

    			// make cube invisible and set fixed camera as active camera
    			test->setVisible(false);
    			smgr->setActiveCamera(fixedCam);

    			// draw whole scene into render buffer
    			smgr->drawAll();

    			// set back old render target
    			driver->setRenderTarget(0);

    			// make the cube visible and set the user controlled camera as active one
    			test->setVisible(true);
    			smgr->setActiveCamera(fpsCamera);
    		}

    		// draw scene normally
    		smgr->drawAll();
    		env->drawAll();

    		driver->endScene();
    	}

    	if (rt)
    		rt->drop(); // drop render target because we created if with a create() method

    	device->drop(); // drop device
    	return 0;
    }