From: "Matt Ebb" <m...@mke3.net> >> Matt proposes a Sample_F output here but it's not entirely clear to me >> how this works, I also couldn't understand from the Houdini >> documentation for example if their BSDF F value is just a >> vector/scalar value or also contains information on how to sample it. > > I've done some research on this, and I think I have a fair idea of > what's going on in there. I actually suspect it's quite similar to > what I was toying around with before [1]. Rather than containing > merely values, the brdf type probably contains some function pointers > to pre-made functions (i.e. lambert distribution, phong distribution, > etc), since that's really the only way to represent a Scattering > Distribution _Function_. It also contains some other flags to say what > kind of scattering it can represent (diffuse, glossy, specular, > emission) etc, and probably some custom data to represent bsdf > parameters (like a glossiness slider). > I'm guessing this via a few VEX functions: > * sample_bsdf() [2] that takes a bsdf, 2d random samples, and shading > geometry as input, and returns an outgoing vector - eg. for lambert a > cosine weighted vector in hemisphere, and > * eval_bsdf() [3] which takes a bsdf and shading geometry input and > returns a colour (proportion of light that's reflected) - eg for > lambert, L.N .
Just a thought, In the literature, it is common to name the BRDF as a function f in equations. f usually takes wi and wo as parameters: the incident and the exitant vectors and it returns the proportion of incoming radiance that is reflected back in wo direction. Also written as f(wi -> wo) to better indicate the direction. All other surface properties and geometries are implicit. Maybe the Houdini F comes from that? Yves _______________________________________________ Bf-committers mailing list Bf-committers@blender.org http://lists.blender.org/mailman/listinfo/bf-committers