Chapter 9 - Multiple rendering passes

Abstract

This chapter provides some useful insights about OpenGL as a programming language for implementing graphics algorithms. The ability to render a primitive multiple times using different modes, and combining the results together to produce the final image is one of the most powerful features of the OpenGL. In essence, a multipass approach combines the individual functional elements of OpenGL into a programming language, thereby increasing the power and generality of the implementation. An application can do more computations than can be performed in OpenGL during a single pass over each primitive, and can achieve a wide variety of additional effects. Using multiple rendering passes to draw a single frame can significantly impact the rendering process, which can lead to unacceptable frame rates. As the raw performance of graphic hardware improves, applications can budget multiple rendering passes to increase the frame quality, yet still maintain their desired frame rate. Investing computation time on multipass algorithms can often yield more improvement to image quality than applying it to increasing polygon counts.