Overview

The algorithms discussed in the previous chapter directly compute the intensity of light passing though the pixels of the virtual screen. In contrast, this chapter covers methods that compute a so-called world space representation of the illumination in a three-dimensional scene. Very often, this object space representation consists of the average diffuse illumination on triangles or convex quadrilaterals into which a three-dimensional model has been tessellated. There are, however, plenty of other possibilities, too. Since diffuse illumination is best modeled by a quantity called radiosity (see Section 2.3.1), such methods are usually called radiosity methods.

The main advantage of computing the illumination in object space is that generating new views of a model takes less work, compared to rendering from scratch. For instance, graphics hardware can be used for real-time rendering of an illuminated model, with colors derived from the precomputed average diffuse illumination. Also, path tracing can be augmented to exploit precomputed illumination in object space, allowing very high image quality. The combination of path tracing after a radiosity method is an example of a two-pass method. Two-pass methods, and other hybrid methods, are the topic of Chapter 7.

The most well-known algorithm for computing an object space representation of illumination is the classic radiosity method [56, 28, 133]. In this chapter, we will present a brief overview of the classic radiosity method (Section 6.1). More introductory or more in-depth coverage of the classic radiosity method can be found in textbooks...