Advanced Graphics Programming Using OpenGL

CHAPTER 9

Multiple Rendering Passes

One of the most powerful features of the OpenGL pipeline is the ability to render a primitive multiple times using different modes, combining the results together to produce the final image (Figure 9.1). This approach implements the equation I_final = I₁op₁ I₂ op₂ … I_n, where op_i represents an arbitrary combining operation. In essence, a multipass approach combines the individual functional elements of OpenGL into a programming language, 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.

Figure 9.1 Basic multipass concept: combine computations ...