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)