Rendering to texture (RTT) in CEGUI

Written for CEGUI 0.8

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Works with versions 0.8.x (stable)

Works with latest CEGUI stable!

Since version 0.8 the new GUIContext class allows it to render your CEGUI interface into a texture instead of rendering it normally into your main buffer.

CEGUI::System& ceguiSystem = CEGUI::System::getSingleton();
 
//Taking some random values as example for a GUIContext size.
int width = 1024;
int height = 800;
CEGUI::Sizef size(static_cast<float>(width), static_cast<float>(height));
 
// We create a CEGUI texture target and create a GUIContext that will use it.
CEGUI::TextureTarget* renderTextureTarget = ceguiSystem.getRenderer()->createTextureTarget();
CEGUI::GUIContext& renderGuiContext = ceguiSystem.createGUIContext(static_cast<CEGUI::RenderTarget&>(*renderTextureTarget) );
renderTextureTarget->declareRenderSize(size);

The following section is only necessary if you want to use the rendered texture as a CEGUI Image again. Basically to render a CEGUI layout inside CEGUI. This won't be the case if you just want to render CEGUI into a texture and use it somewhere in your 3D application.

// We create a BasicImage and set the Texture
CEGUI::BasicImage* textureTargetImage = static_cast<CEGUI::BasicImage*>(&CEGUI::ImageManager::getSingleton().create("BasicImage", "MyTextureGroup/MyTextureName"));
textureTargetImage->setTexture(&renderTextureTarget->getTexture());
 
//Flipping is necessary due to differences between renderers regarding top or bottom being the origin
bool isTextureTargetVerticallyFlipped = renderTextureTarget->isRenderingInverted();
CEGUI::Rectf renderArea;
 
if (isTextureTargetVerticallyFlipped)
    renderArea = CEGUI::Rectf(0.0f, height, width, 0.0f);
else
    renderArea = CEGUI::Rectf(0.0f, 0.0f, width, height);
 
textureTargetImage->setImageArea(renderArea);

For rendering you need to call the rendering function of your new GuiContext directly. Here is an example of how to call the renderer and the guicontext in the right order when rendering:

    CEGUI::Renderer* gui_renderer(gui_system.getRenderer());
    gui_renderer->beginRendering();
 
    renderTextureTarget->clear();
    renderGuiContext.draw();
 
    gui_renderer->endRendering();

Also do not forget to correctly update CEGUI and the GUIContext with all timepulses and inputs, just as you would do it normally but by using your new GUIContext instead of the default one!

If you want to retrieve the renderer-specific texture from a CEGUI texture you will need to cast it:

For example for OpenGL:

CEGUI::OpenGLTexture& glTexture = static_cast<CEGUI::OpenGLTexture&>(d_textureTarget->getTexture());

After that you can use the member function to receive whatever render-specific traits you need, such as the textureID in Opengl as an unsigned integer, etc.