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# 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.

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 "driverChoice.h"

    using namespace irr;

    #ifdef _MSC_VER
    #pragma comment(lib, "Irrlicht.lib")
    #endif

    int main()
    {
            // ask user for driver
            video::E_DRIVER_TYPE driverType=driverChoiceConsole();
            if (driverType==video::EDT_COUNT)
                    return 1;

            // create device and exit if creation failed

            IrrlichtDevice *device =
                    createDevice(driverType, core::dimension2d<u32>(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));
                    fairy->setMD2Animation ( scene::EMAT_STAND );
            }

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
            smgr->addLightSceneNode(0, core::vector3df(-15,5,-105),
                            video::SColorf(1.0f, 1.0f, 1.0f));

            // set ambient light
            smgr->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::addRenderTargetTexture() 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. 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->addRenderTargetTexture(core::dimension2d<u32>(256,256), "RTT1");
                    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 it, wasn't too complicated I hope. :)

            int lastFPS = -1;

            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
                            // The buffer might have been distorted, so clear it
                            driver->setRenderTarget(0, true, true, 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();

                    // display frames per second in window title
                    int fps = driver->getFPS();
                    if (lastFPS != fps)
                    {
                            core::stringw str = L"Irrlicht Engine - Render to Texture and Specular Highlights example";
                            str += " FPS:";
                            str += fps;

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

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

| The Irrlicht Engine Documentation © 2003-2010 by Nikolaus Gebhardt. Generated on Sun Feb 14 13:06:59 2010 by Doxygen (1.6.2)