“Filter Glossy” basically pretends glossy bounces from surfaces with a roughness > 0, i.e. there is some randomness to the light path’s bounce direction, instead of a perfectly specular bounce from a sharp mirror.
This means caustic paths are much easier to find, but also that they are blurred.
It’s basically designed to sidestep this issue with SDS paths (among other things) - the only reason it’s sensible is because, with regular Cycles up until now, Caustics were practically useless anyway. Might as well make use of those paths in ways the path tracing algorithm can actually handle instead of just entirely losing that energy.
With these shiny new rendering techniques that may be far less necessary though. To get this many caustics this cleanly after just 55 SPP is quite insane. - If you look at my render with 500SPP you’l see caustics basically don’t exist at all yet beyond noise, and even the much higher sample rate render looks noisy (though at least you can tell what the caustics ought to be)
Maybe you should try re-rendering your volumetric scene with Filter Glossy and Indirect clamping turned off too
@sherholz btw, just in case that is of use to you and you somehow don’t already have an equivalent test, feel free to use that scene as ever you see fit. I’ma say it’s CC0
Gotta compare to the equivalent version without PG - honeslty, while noisy, it doesn’t look too bad
It’s also slightly brighter than the versions you rendered before, but that’s perhaps to be expected with the indirect light not clamped
EDIT: nice to see that it definitely reduces noise in this scenario as well
Ok based on this one scene at least, it looks like it takes about 50% longer to render, which is quite a lot, but then it really isn’t, considering it’d have taken literal ages to render this with that much clarity before. If it had ever happened.
This is a huge step forward. Very glad Cycles is getting this!
Not only that, but this is using an early version of OpenPGL. If it goes the same way as OIDN, then we should only see better results in the future (in the same timeframe).
In order to get a better sense of what PG has to offer compared to what’s there today, it would be better to use the “Time Limit” option for rendering instead of the sample count. Compare what a 1 minute render looks like with PG off and then on etc. It will also help you discover cases like you observed above where the cost per sample is higher with PG etc.
It will yield better insight into the actual cost for typical scenes and is much more relatable since sample counts vary from scene to scene. All that matters sometimes is that you have a budget of “x” for each frame, so evaluate what can be achieved after rendering for “x” time.
MNEE overwrites the refractive result when both PG and MNEE are on. And MNEE is not finding the right path I think, MNEE is producing the wrong result. This is rather interesting.
This should be posted as bug report,if the branch gets into the master.
The refraction calc inclusive the ray exit angle should be not that hard.
Since @sherholz is working on this PG,maybe he is not aware of the nested dielectrics problem.If this gets fixed too, it would increase the realisim of lighttransport in glass and liquids even more.
