Comments on: Multiple Scattering

By: Iliyan

Iliyan — Fri, 22 Jun 2012 09:29:56 +0000

I agree it can be a bit confusing in the beginning. But it’s essentially a slight extension of Veach framework, where a path vertex can not only lie on a surface, but can also be in a medium. Thus the path vertex measure is either area or volume, and is specified using the characteristic bit vector. Additionally, in the geometric you generalize the binary visibility term to the transmittance between the two points (which is 0 if the connecting line intersects an opaque object). You make the BSDF to also handle volumetric scattering (via the phase function) and that’s it. That’s all to Pauly’s path integral extension.

By: Simon Brown

Simon Brown — Thu, 21 Jun 2012 19:57:20 +0000

You only need to add the distance sampling, which results in slightly different pdf if the point ends up being in the medium or on a surface, but that’s essentially it.

Well maybe it’s just my maths that are a bit rusty then, I didn’t find the new path space measure to be trivial, but that’s essentially it.

By: Iliyan

Iliyan — Thu, 21 Jun 2012 19:44:03 +0000

What is so different with the MIS weights? You only need to add the distance sampling, which results in slightly different pdf if the point ends up being in the medium or on a surface, but that’s essentially it. The directional sampling is either BSDF or a phase function, which can be encapsulated in the implementation. It becomes much more nasty with inhomogeneous media, where it’s impossible to exactly compute distance pdfs, cause they are integrals themselves (assuming transmittance based distance sampling). Actually, adding participating media on top of a working bidirectional path tracer is surprisingly straightforward.