Cycles: Implement approximate reflectance profiles
Using this paper:
http://graphics.pixar.com/library/ApproxBSSRDF/paper.pdf
This model gives less blurry results than the Cubic and Gaussian
we had implemented:
- Cubic: https://developer.blender.org/
F279670
- Burley: https://developer.blender.org/
F279671
The model is called "Christensen-Burley" in the interface, which
actually should be read as "Physically based" or "Realistic".
Reviewers: juicyfruit, dingto, lukasstockner97, brecht
Reviewed By: brecht, dingto
Subscribers: robocyte
Differential Revision: https://developer.blender.org/D1759