What is exactly is BRDF. I know it has to do with rendering and lighting. I am reading about Subsurface scattering and it mentions BRDF ALOT!

Bidirectional Reflectance Distribution Function.

The BRDF determines the intensity of the reflected light for an incoming direction of light.

In vex diffuse() and specular() can be considered solutions to a BRDF.

Roy Hall wrote a good book on the subject called, Illumination and Color in Computer Generated Imagery, larger University libraries may have a copy sitting around.

jim.