Multipass Algorithms

One useful effect of making the framebuffer explicit is that it enables the use of multipass algorithms, in which the same primitives are rendered several times. One example of a multipass algorithm employs an accumulation buffer[3]: a scene is rendered several times, each time with a slightly different view, and the results averaged in the framebuffer. Depending on how the view is altered on each pass, this algorithm can be used to achieve full-window anti-aliasing, depth-of-field effects, motion blur, or combinations of these. Multipass algorithms are simple to implement in OpenGL, because only a small number of parameters must be manipulated between passes, and changing the values of these parameters is both efficient and without side effects on other parameters that must remain constant.