A lot of these physically based models have papers which draw comparisons to another shading model called Cook Torrance. Cook Torrance has quite a few features which make it an attractive physical model: it features a roughness term like Oren-Nayar, and a frensel term that modifies the specular highlight based on viewing angle. Additionally, it calculates self shadowing from micro facets similarly to Strauss. It seems very similar to Strauss actually, and incorporates a lot of the same concepts. For my implementation I used Beckmann Distribution to calculate roughness and Schlick’s approximation for the Frensel.
One of the most interesting things is it’s use of the frensel, which directly contributes to the diffuse and specular highlights. When the frensel reflection an roughness are set to 1 , it looks a lot like the frensel i’ve been adding to the diffuse for a while, albeit modeled much more nicely. Cook Toorance on the left, modified phong on the right.
I’m just going to go ahead and pretend that it wasn’t a complete hack and was exactly what i was going for in the first place ^_^
Maya CGFX File:
| cooktorrance.cgfx |
Unity SHADER File:
| cooktorrance.shader |