KHR_materials_pbrThinFilm extension

[UX3D-nopper]

We are currently working on a "Thin Film" extension based on these papers:
https://belcour.github.io/blog/research/2017/05/01/brdf-thin-film.html
http://blog.selfshadow.com/publications/s2017-shading-course/drobot/s2017_pbs_multilayered.pdf

Would be great, to have it as a KHR_ extension.

[donmccurdy]

Is this equivalent to "clear coat", mentioned in #1040 and Blender's Principled BSDF node?

[bhouston]

The simple version of this is equivalent to clear coat as implemented in ThreeJS and UE4. The issue is clear coat in Three.JS should have a larger range. It should be called that as well.

[donmccurdy]

Closing this issue to keep discussion in #1742.