FrameBufferObjects
A common feature in 2D and 3D graphics programming is the ability to render to a texture. For example, say we have a slider GUI component made up of multiple sprites (the track, and the thumb button), and we are trying to fade it in/out. When we render each sprite at 50% opacity, we get some ugly blending where the sprites meet. The solution is to render the entire component at 100% opacity to an "offscreen texture", then render the offscreen texture to the screen at 50%.
(Slider PSD can be downloaded here)
Another use for render-to-texture is for post-processing effects; i.e. rendering your sprites to an offscreen texture as large as the game window, and then render that texture to the screen
In OpenGL, in order to render to texture, we need to set up a Frame Buffer Object (FBO). We will use the Framebuffer utility to make things a bit easier. You can loosely think of FBOs as a means of "switching screens" in GL. Generally you render to the default "screen" of the Display (or back buffer), but with an FBO you can define other screens to render to.
First, we create a new frame buffer object:
fbo = new Framebuffer(512, 512);For maximum compatibility and efficiency, you should stick to power-of-two sizes. The frame buffer is backed by a texture, so it has the same hardware limitations discussed in the Textures tutorial.
A frame