Translucency rendering differences between GPU and CPU

[EgertKanep]

.blend file:

volume_problem.zip

Steps to reproduce:
Render 2 versions one with gpu and cpu. Differences only occur when using volume in combination with translucent material, if using null instead of translucent material I get same results

Screenshots or rendered images:
CPU

GPU

Error message from Blender console:

OS: Rocky Linux 9
Blender version: 4.2.7 lts
LuxCore version: 2.10.0 alpha1

[CodeFHD]

Moved to LuxCore because this is most likely a core issue.

Also possibly related to #647

[EgertKanep]

I ran a similar scene in Bledner LTS 2.93 and the latest LuxCore 2.6. There it did not happen with cpu and gpu(opencl)

[CodeFHD]

Yes I think this is a PathOCL equivalent to #647, which was specifically about BiDir.

The test scene you provided has a rather large scattering scale on the interior volume of the inner cube, which means light should effectively not pass it. This is visualized when hiding the outer cube and viewing from the top, see screenshot below.

Even when exaggerating this by setting absorption color to black and absorption distance to 0.01, the cube remains completely lit with GPU rendering.

The hint about v2.6 is interesting. At first glance, none of the source files that I would primarily associate with this have been changed since the release of v2.6.

[CodeFHD]

@EgertKanep I can reproduce the issue in v2.6 as well.

Could you please check your v2.6-test scene regarding scattering scale and absorption?

[EgertKanep]

@EgertKanep I can reproduce the issue in v2.6 as well.

Could you please check your v2.6-test scene regarding scattering scale and absorption?

Yes, you are correct, I rebuild the scene wirh identical parameters and it happens when using path with opencl.