The constant variable, levels, defines how many distinct values will be used in the diffuse calculation. This could also be defined as a uniform variable to allow for configuration from the main OpenGL application. We will use this variable to quantize the value of the cosine term in the diffuse calculation.
The toonShade function is the most significant part of this shader. We start by computing s, the vector toward the light source. Next, we compute the cosine term of the diffuse component by evaluating the dot product of s and Normal. The next line quantizes that value in the following way. Since the two vectors are normalized, and we have removed negative values with the max function, we are sure that the value of cosine ...
