Following where light bounces
PBR is based on the actual physics of light rather than the other relatively simple lighting model of Lambert, examined in Chapter 5, Let’s Light It Up! PBR is a concept rather than a specific algorithm and can be achieved using a variety of mathematical models. To understand how PBR works, we need to understand some key fundamentals about the visual way light works.
Light is a ray we can represent with vectors relative to the normal of the surface being hit, as shown in Figure 19.1:
Figure 19.1: An incident and reflection ray
The light coming in from the source is called the incident ray and the light being reflected from the surface is called the reflection ray. According to the law of reflection, the angle of incidence is equal to the angle of reflection. Both rays travel in a straight line, and whether the strength of the incoming ray is the same as the reflected ray depends on what happens at the point of collision...
