Chapter 14. Surface Characteristics

Up to this point, we have primarily been modeling surface reflection in a simplistic way. The traditional reflection model is simple enough to compute and gives reasonable results, but it reproduces the appearance of only a small number of materials. In the real world, there is enormous variety in the way objects interact with light. To simulate the interaction of light with materials such as water, metals, metallic car paints, CDs, human skin, butterfly wings, and peacock feathers, we need to go beyond the basics.

One way to achieve greater degrees of realism in modeling the interaction between light and surfaces is to use models that are more firmly based on the physics of light reflection, absorption, and transmission. Such models have been the pursuit of graphics researchers since the 1970s. With the programmable graphics hardware of today, we are now at a point where such models can be used in real-time graphics applications to achieve unprecedented realism. A performance optimization that is often employed is to precompute these functions and store the results in textures that can be accessed from within a shader. A second way to achieve greater degrees of realism is to measure or photograph the characteristics of real materials and use these measurements in our shading algorithms. In this chapter, we look at shaders based on both approaches.

In addition, we have not yet looked at any shaders that allow for the transmission of light through a surface. This is our first example as we look at several shaders that model materials with differing surface characteristics.