Cook-Torrance Specular Reflectance Model

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This demo renders the Utah teapot with a specular component, but no diffuse component. When compared to Blinn or Phong specular reflection, the Cook-Torrance model provides a more physically-based computation. The Blinn and Phong approaches use basic mathematical approximations of the specular color based on the viewing angle. The Cook-Torrance approach accounts for masking/shadowing, microfacet distribution, and interreflection from these microfacets. This allows for much more variability in color across the specular highlights of the object rendered. The RGB color is derived from the metal's real and imaginary refractive indices chosen at three wavelengths (630 for red, 533 for green, and 473 for blue). These refractive indices are used in calculating the Fresnel reflectance. The Fresnel reflectance is scaled by the distribution function, and the masking approximation. The result is then inversely scaled by terms representing how much of the surface is visible to the light source and how much of the surface is visible to the viewer.

For best results, turn on the light rotation and view the lid portion of the teapot. The specular reflections of gold, copper, and cobalt all look realistic.