Possible NaNs with refractive BSDF
Closed, ResolvedPublic

Description

System Information
i7 3930k
40GB RAM
Nvidia GeForce GTX660 (driver version 21.21.13.7653)
windows 10 pro, 64-bit

Blender Version
2.78a e8299c8

Short description of error
cycles renders artifacts, that look like NaN errors: see image

Exact steps for others to reproduce the error
open scene

, set viewport to "Rendered" or press f12 to render, while it's cooking, these white dots start to pop up

Details

Type
Bug

Doesn't look like a bug, just reflections from the lamp. Disable MIS for the lamp and the birght spots go away.

@Sergey Sharybin (sergey) Can you confirm?

Sergey Sharybin (sergey) triaged this task as Confirmed priority.Feb 23 2017, 11:42 AM
Sergey Sharybin (sergey) claimed this task.

The noise is coming from caustics i think. Usually using Filter Glossy will help, but it has no effect on Sharp distribution. Doing something like D2416 will help here.

At least that's what i see from quick investigation and might be wrong.

In any case, unsolvable noise is not a good thing anyway and disabling MIS is not really a solution in real production scenes.

Maybe @Brecht Van Lommel (brecht) can throw some ideas here as well :)

I think D2416 would be good for this case.

The other workaround is to use the transparent shadows trick, which might be good to add as a builtin feature of the glass BSDF node:
https://docs.blender.org/manual/en/dev/render/cycles/optimizations/reducing_noise.html#glass-and-transparent-shadows

Sergey Sharybin (sergey) closed this task as Resolved.Feb 27 2017, 12:45 PM

I've fixed some issues in D2416 and committed it now. So now there is a way to make his file to be less noisy.

Surely having some built-in feature for transparent shadow for BSDF will be interesting, but think that's out of the scope of this report.