Blender Git Loki

Cycles: Add a roughness variable to ShaderClosures to be used for the denoise feature heuristic

To produce better results for sharp reflections/refractions, the denoise features are only written at the first
rough/diffuse bounce. To determine whether the current bounce is rough/diffuse or not, the roughness of the individual
closures will be used.
Also, the PathState tracks the total length of the path, for the same reason (it might not be written at the first bounce).