Multiscatter GGX Glass Shader - In a certain range of roughnesses, specular reflections darken/disappear. #96602

New Issue

tempdevnova · 2022-03-18T17:38:19+01:00

tempdevnova commented

2022-03-18 17:38:19 +01:00

System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07

Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: f1cca30557
Worked: (newest version of Blender that worked as expected)

Short description of error
When using the Glass and Glossy BSDF with Multiscatter GGX and a roughness of around 0.02 the specular reflection somehow breaks, which is visible as excessive darkening.

In the images below, I have applied a gradient roughness texture starting at 0 at the top and 1 at the bottom. As you can see in the Multiscatter GGX there is a dark "seam" near the top of image that isn't present with GGX and probably shouldn't be there.


Multiscatter GGX	GGX

Exact steps for others to reproduce the error
Multitest.blend

In this test file only the specular reflection is visible. The gradient going into the roughness input goes from 0 at the top to 1 at the bottom. As can be seen there is a sudden dip at a roughness value of around 0.02. It is also visible without the gradient when simply entering values of around 0.02 into the roughness input.

This problem is exclusive to Multiscatter GGX and does not occur with other microfacet distribution models.
Edit: The same problem has been found with the Glossy BSDF.

Thank you and have a great day!

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `f1cca30557` Worked: (newest version of Blender that worked as expected) **Short description of error** When using the Glass and Glossy BSDF with Multiscatter GGX and a roughness of around 0.02 the specular reflection somehow breaks, which is visible as excessive darkening. In the images below, I have applied a gradient roughness texture starting at 0 at the top and 1 at the bottom. As you can see in the Multiscatter GGX there is a dark "seam" near the top of image that isn't present with GGX and probably shouldn't be there. |![#96602 - Multiscatter darkened reflections.png](https://archive.blender.org/developer/F12939300/T96602_-_Multiscatter_darkened_reflections.png)|![#96602 - GGX no darkening.png](https://archive.blender.org/developer/F12939305/T96602_-_GGX_no_darkening.png)| | -- | -- | |Multiscatter GGX|GGX| **Exact steps for others to reproduce the error** [Multitest.blend](https://archive.blender.org/developer/F12933486/Multitest.blend) In this test file only the specular reflection is visible. The gradient going into the roughness input goes from 0 at the top to 1 at the bottom. As can be seen there is a sudden dip at a roughness value of around 0.02. It is also visible without the gradient when simply entering values of around 0.02 into the roughness input. This problem is exclusive to Multiscatter GGX and does not occur with other microfacet distribution models. Edit: The same problem has been found with the Glossy BSDF. Thank you and have a great day!

tempdevnova commented

2022-03-18 17:38:19 +01:00

Added subscriber: @tempdevnova

Alaska commented

2022-03-19 02:36:15 +01:00

Added subscriber: @Alaska

Alaska commented

2022-03-19 02:36:15 +01:00

Changed status from 'Needs Triage' to: 'Confirmed'

Alaska commented

2022-03-19 02:36:15 +01:00

I can confirm this issue.

System Information
Operating system: Linux-5.16.0-3-amd64-x86_64-with-glibc2.33 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54
Broken version: 3.2.0 Alpha, branch: master, commit date: 2022-03-17 21:23, hash: 6d97a5f93c

I can confirm this issue. **System Information** Operating system: Linux-5.16.0-3-amd64-x86_64-with-glibc2.33 64 Bits Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54 Broken version: 3.2.0 Alpha, branch: master, commit date: 2022-03-17 21:23, hash: `6d97a5f93c`

Alaska commented

2022-03-22 04:41:22 +01:00

Closed as duplicate of #82500

Alaska closed this issue

2022-03-22 04:41:22 +01:00

Alaska commented

2022-03-22 04:43:52 +01:00

Changed status from 'Duplicate' to: 'Confirmed'

Alaska reopened this issue

2022-03-22 04:43:52 +01:00

Alaska commented

2022-03-22 04:43:52 +01:00

Sorry, I merged the wrong task.

Alaska commented

2022-03-22 04:49:12 +01:00

Added subscriber: @brecht

Alaska commented

2022-03-22 04:49:12 +01:00

@brecht are you able to look at this and confirm if this is a bug, or a limitation of Multiscatter GGX. If it is a bug, is it related to other reports? (E.G. #82500, #85259, #92520)

Alaska changed title from ~~The Multiscatter GGX issues trilogy (part 1 of 3 (Glass BSDF))~~ to Multiscatter GGX Glass Shader - In a certain range of roughnesses, specular reflections darken/disappear.

2022-03-22 04:54:17 +01:00

Philipp Oeser removed the

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Multiscatter GGX Glass Shader - In a certain range of roughnesses, specular reflections darken/disappear. #96602