9.5.2

938 • CHAPTER 18
THE SHADERS • 939
Diffuse page
The Diffuse group applies to the currently selected surface in the surface combo box below the
preview.
Color
Sets the base diffuse color of the surface.
Algorithm
Species which illumination model will be used. The drop-down list provides for two choices, including
Internal, which is the standard Lambertian model, and the Oren Nayar model, which provides for
a roughness variable, allowing the user to go from simple surfaces (0 Roughness, identical to
Lambertian), to complex rough surfaces (100% + Roughness, which provides for a surface, such as
linen or dirt).
Roughness
Dictates how rough the Oren Nayar illumination model will be. Zero is no roughness while 100% or
greater is very rough. Experimentation is required to fully understand this parameter. This option is
only available if Oren Nayar is selected in the Algorithm drop-down list.
Illumination
Scales the Diffuse Color to produce attenuation in the illumination of the surface (this simply means it
makes the color darker when the value is close to zero and brighter when the value is closer to 100%
or above). If you are utilizing the Oren Nayar illumination algorithm you may want to bump up the
illumination about 10% to 20% because it renders darker usually. Appropriate values are between
0% and 200%.