Incorrect excessive darkening of volumetrically scattered light when combined with see-through shaders #105637

New Issue

tempdevnova · 2023-03-10T15:11:17+01:00

tempdevnova commented

2023-03-10 15:11:17 +01:00

System Information
Operating system: Windows 10
Graphics card: Nvidia GTX 1080

Blender Version
Broken: 3.3.1

Short description of error
When using any kind of volume scattering (Volume Scatter and Principled Volume node) in combination with any of the following see-through shaders: Refraction BSDF, Glass BSDF and Principled BSDF will cause incorrect excessive darkening of the volumetrically scattered light. This is not the case when using the Transparent BSDF.

Exact steps for others to reproduce the error
See test .blend file:
Volume_Bug.blend
The cases are labeled in the shader editor.

**System Information** Operating system: Windows 10 Graphics card: Nvidia GTX 1080 **Blender Version** Broken: 3.3.1 **Short description of error** When using any kind of volume scattering (`Volume Scatter` and `Principled Volume` node) in combination with any of the following see-through shaders: `Refraction BSDF`, `Glass BSDF` and `Principled BSDF` will cause incorrect excessive darkening of the volumetrically scattered light. This is not the case when using the `Transparent BSDF`. **Exact steps for others to reproduce the error** See test .blend file: [Volume_Bug.blend](/attachments/a0b05b9a-4959-405c-a4f8-3c731d488ea3) The cases are labeled in the shader editor.

Volume_Bug.blend

1.0 MiB

tempdevnova added the

labels 2023-03-10 15:11:18 +01:00

tempdevnova changed title from ~~Incorrect darkening of volumetrically scattered light when combined with see-through shaders~~ to Incorrect excessive darkening of volumetrically scattered light when combined with see-through shaders

2023-03-10 15:13:41 +01:00

Germano Cavalcante commented

2023-03-11 00:21:14 +01:00

Unfortunately this is a limitation with the shadow of these materials since the Cycles path tracing integrator is not very good at rendering caustics.

The manual tells more about this limitation, and here is a suggestion to work around it:
https://docs.blender.org/manual/en/latest/render/cycles/optimizations/reducing_noise.html#render-cycles-reducing-noise-glass-and-transp-shadows

However I'm not sure why the shadow gets so dark even with IOR 1.0.

It would be interesting to get input from the developers for this case.

Unfortunately this is a limitation with the shadow of these materials since the Cycles path tracing integrator is not very good at rendering caustics. The manual tells more about this limitation, and here is a suggestion to work around it: https://docs.blender.org/manual/en/latest/render/cycles/optimizations/reducing_noise.html#render-cycles-reducing-noise-glass-and-transp-shadows However I'm not sure why the shadow gets so dark even with IOR `1.0`. It would be interesting to get input from the developers for this case.

Germano Cavalcante added

Module

Render & Cycles

Status

Needs Info from Developers

and removed

Status

Needs Triage

labels 2023-03-11 00:21:38 +01:00

Fernando Alcala commented

2023-03-11 06:18:56 +01:00

Turning Path Guiding on and turning Filter Glossy off will get the light back in glass materials.

Turning `Path Guiding` on *and* turning `Filter Glossy` off will get the light back in glass materials.

2m50s glass 256pg filterglossy on.png

527 KiB

17s tran no pg.png

517 KiB

29s glass pg off filterglossy off.png

529 KiB

33s glass no pg.png

527 KiB

1m29s glass 256pg filterglossy off.png

523 KiB

Steve commented

2023-03-11 12:44:03 +01:00

Also volume bounce at 0 isn't helping I guess

Screenshot_2.png

9.7 KiB

Germano Cavalcante commented

2023-03-13 22:18:24 +01:00

Since this is a path tracing limitation, and can be work around with Path Guiding and Volume Bounces, it is not worth keeping this report open.

Thanks for the feedback.

Since this is a path tracing limitation, and can be work around with `Path Guiding` and `Volume Bounces`, it is not worth keeping this report open. Thanks for the feedback.

Germano Cavalcante closed this issue

2023-03-13 22:18:31 +01:00

Blender Bot added

Status

Archived

and removed

Status

Needs Info from Developers

labels 2023-03-13 22:18:32 +01:00

tempdevnova commented

2023-03-14 19:00:40 +01:00

Ok, thanks everyone for investigating!

I know this isn't the right place to ask this, but since it's a caustics problem can it be solved with Blender's new "Cast Shadow Caustics" and "Receive Shadow Caustics" options?

Ok, thanks everyone for investigating! I know this isn't the right place to ask this, but since it's a caustics problem can it be solved with Blender's new "Cast Shadow Caustics" and "Receive Shadow Caustics" options?

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Incorrect excessive darkening of volumetrically scattered light when combined with see-through shaders #105637