jparker
But did you know, when using PBR, you can layer an arbitrary number of surface model VOPS, using mix, add or whatever, with a very small cost in render time?
Yep, and I really like it.
This is a HUGE benefit to mantra, that BSDF models can be mixed so easily in VEX without a large performance hit, If you don't like the specular lobes you get from the built in bsdf models you can just layer several together to shape it the way you want. How many other renderers will allow this kind of free “bsdf sculpting”?
Yes, Mantra was actually the first commercial production grade renderer with such ability, to my knowledge.
More in general OSL solves this “by design” since you code in the renderer the BSDF and you don't do anymore light loops. Blender Cycles is able to do so and I believe Sony's proprietary Arnold supports it too. Appleseed can do it too but there is no shading language (yet). I am sure many others can be added to the list.
Shading language wise I expect this to be possible in RSL-based renderers: 3Delight's Path Tracer now has hardcoded BSDFs so as soon as you can avoid using illuminance() this will go to town. Same for PRMan.
As a long time lookdev artist, to me this is a ‘killer’ feature, and obviates the need for a multilayer node.
I was more referring at layering multiple materials each with a thickness and energy interchange, but in term of layering/shaping of specular yes this is absolutely cool.