I am a little bit confused about the various flavors of material layering in both online and offline rendering. I had naively assumed (after using the Mix Shader in Cycles and a few minutes in Substance Painter) that material layering was just a simple mask channel that blended between the final colors, sort of like texture splatting for terrain.
But reading this question I see that the actual shader inputs are interpolated, rather than the final colors:
Is this the same process for offline renderers? Reading the man page for RenderMan it seems like it is, as they specify only similar Bxdfs can be mixed:
Are there any papers that describe the basics? I found this from SIGGRAPH last month, but it confused the hell out of me:
Lastly, are there any contexts in which material layering is simulation of multiple physical interfaces? Or is that referred to something else, like nested dielectrics?