:DESCRIPTION:
The Lafortune shader is based on the renderman shader by Stephen H. Westin and the research paper Non-linear approximation of reflectance functions. The shader introduces a new class of primitive functions with non-linear parameters
for representing light reflectance functions. The functions are reciprocal, energy-conserving and expressive. They can capture important phenomena such as off-specular reflection, increasing re-flectance and retro-reflection.