guibou wrote:In fact, using the knaus PPM approach (know as PPM proba is luxrender), the radius per pass in known in advance (in fact, the radius is only a function of the pass number, ie: Radius(i) = Radius(i - 1) * (i - alpha) / (i - 1)), so the master only have to ask each slave to render a specific pass and it works.
The issue is how to handle slaves which are taking too much time to finish the pass they where asked for. Should we ask a new slave to compute the pass ? If twos slaves are working on the same pass and gives a result, can we stupidly merge both passes and normalize the number of photons ?
Same think, if we want to implement flm merging, each flm should stores the id of each pass it contains. But how to handle duplicates ?
In an ideal world to get the most out of SPPM, yes we need this. However if we accept a global performance loss, we can do without much of this information. We can have 2 slaves computing the same pass number at the same time, that's not a problem, what is important is that the photon density is correctly computed and preserved during merging. Not correctly accounting the pass number or the radius might lead to a slower radius reduction, but the variance will still be reduced.
guibou wrote:Yes, glossy surfaces are tricky. An important part of the research done in rendering algorithm nowadays focus on better handling of glossy reflections.
Yes, just to put some light on the subject:
- matte (lambertian) surfaces reaction is the same in every direction so the colour mostly depends on the surrounding lights (thus the direct lighting algorithms)
- specular surfaces reflects light in a single direction, so it is quite easy to bounce light and follow a path
- glossy surfaces are in between, they can have a very strong reflection around a single direction, but if there is no light in that direction but a strong light outside, most of the perceived illumination will come from that outlying light.
Glossy surfaces reaction is really dependent on the product of the surface BSDF and the surrounding illumination, thus the great number of research papers on integrating products of functions.