Feature Request: importance sampling visible normal of anisotropic ggx

[f1shel]

Hi! I notice that SampleGGXVNDF is used to sample ggx distribution and this method is for isotropic ggx. In some cases (anisotopic != 0) ggx distribution will be anisotropic. Could you please add the anisotropic version of importance sampling?

[knightcrawler25]

Sure. I had some issues earlier getting anisotropy to work correctly so it's disabled in the code right now. Will have another go at it.

[knightcrawler25]

I've added it in:

Limitation: The Tangent and Bitangent are not calculated from the mesh UVs so rotating the mesh will have no effect on the anisotropic specular highlights. However, that won't effect the importance sampling. Let me know if you notice any issues.

[tigrazone]

Please add demo file to repo

[knightcrawler25]

The scene is already available (cornell_box_sphere.scene). Just set anisotropic and metallic to 1.0 for the sphere material