Summary

This chapter may have felt either extremely long, extremely short, or extremely boring, depending on your existing knowledge and experience. The behavior of light in the real world is extremely complicated, so when simulating it in a scene, it’s necessary to make simplifications and assumptions about that behavior.

Traveling in rays from source to destination material, light is modeled using some implementation of the Bi-Directional Reflectance Function (BRDF). This function computes the (ir)radiance or brightness at a given input point and angle from a source of light. The function has a set of terms that are each calculated in separate functions, then combined to provide a result.

The Diffuse term (also called Albedo) accounts for light that has been evenly scattered from the surface of the material, kind of like how a point light evenly projects light in all directions. Specular is the term for light that is reflected from the material directly into the camera...