Multiscatter GGX converges to different result (Path vs Branched Path)
Open, ConfirmedPublic

Description

System:
Debian, amd64

Broken: current master

Description:
Multiscatter GGX converges to a different result in Pathtracing vs branched Pathtracing.
It seems that MIS and "Sample all Lights" don't influence the final outcome but it is only related to Multiscatter GGX.
Here are the results, both rendered with 100000 samples.

Steps to reproduce:
Here is a .blend file:


Make one render with "Path Tracing" and one render with "Branched Path Tracing", then compare both.

Thank you!

Details

Type
Bug

The issue still persists here with build 0f793ee. @Brecht Van Lommel (brecht) did you render my example .blend file before closing this issue?

Tested on Linux now and it does still converge to a different result, maybe something compiler specific. With this many samples to resolve noise I wouldn't be surprised if float precision issues have an effect.

I'm not sure if it is float precision issue, but one can see pretty quickly (after 4000 or 8000 samples) that it will converge to a different result.