The basic problem is that you need to have the entire scene description available to every process, and GPU's don't work that way. They are optimized for SIMD (single-instruction, multiple-data) processing, meaning that you run the same operation on many operands simultaneously. This is great if you are multiplying huge matrices together, but not much use in a ray-tracing context.
Even if the GPU were optimized for this problem, much of what goes on in Radiance is ray tree evaluation. It all sort of happens together -- you need to trace rays, figure out what to do at surfaces based on material properties, evaluate .cal files, share ambient data (reading and writing a shared cache) and all sorts of things that would have to be completely rethought for a GPU implementation.
-Greg
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From: Ignacio Munarriz <[email protected]>
Date: July 12, 2010 11:05:27 AM PDTI'm not aware of any physical simulation of light software using gpu, but probably it would be interesting to externalize ray-geometry intersections in radiance. I think there is already gpu code(as libraries or open source) that makes that intersections. Radiance instances, meshes, memory management ... would be some issues to solve, maybe waiting a bit the ray-geometry intersections will be normalized in gpus and it will be easier to send rays and geometry from radiance to the cards
El 12/07/2010 19:05, R Fritz escribió:
Thank you. That makes it clear that something is possible. But what? As of version 3.5, Mental Ray (the base of iray) had some serious limitations in physically based rendering. In Labayrade and Fontoynont's 2009 CIE 171:2006 testing, it could not, for instance, simulate a clear sky. Iray is based on Mental Ray 3.8, and it is possible that some of those problems have been resolved since version 3.5, but there does not seem to have been any testing published that says so. Mental Image's iray site doesn't mention CIE 171. The Luxrender site doesn't mention any testing at all. Are you aware of any testing that shows accuracy of either of these tools in the physical simulation of light?
Greg, have you looked at this at all?
Randolph