SSS Shader - Black artifacts with intersecting geometry within the same object #81602

New Issue

Fynn Große-Bley · 2020-10-10T15:12:13+02:00

Fynn Große-Bley commented

2020-10-10 15:12:13 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87

Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-19 23:28, hash: 874af5301c
Worked: (newest version of Blender that worked as expected)

Short description of error
While rendering with Cycles using the random walk subsurface scattering parameters I do get black lines/artifacts wherever there is intersecting geometry even when it's the same object. An option where it's possible to define which objects should be treated as one volume for the SSS calculations would be great (and probably treating one object that contains several geometries that are intersecting as one volume). I wasn't sure if that is a feature request or a bug but I don't see a case where that is preferable so I reported it as a bug.

Exact steps for others to reproduce the error
As a test I duplicated the default cube and moved it so the two cubes intersect. I then joined the cubes into one object. I set the subsurface method to 'random walk' and the subsurface slider to '1'. Cycles is used and I added a simple Area light above the cubes to see it better.
[Based on the default startup or an attached .blend file (as simple as possible)]
Attached is the quick test scene with the cubes and a render comparison between cycles in blender and the SSS random walk 2 in maya with arnold (the one with the black edges around the muscles is done with blender/cycles and the clean one is done with maya/arnold)

SSS_blackArtifacts_test.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87 **Blender Version** Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-19 23:28, hash: `874af5301c` Worked: (newest version of Blender that worked as expected) **Short description of error** While rendering with Cycles using the random walk subsurface scattering parameters I do get black lines/artifacts wherever there is intersecting geometry even when it's the same object. An option where it's possible to define which objects should be treated as one volume for the SSS calculations would be great (and probably treating one object that contains several geometries that are intersecting as one volume). I wasn't sure if that is a feature request or a bug but I don't see a case where that is preferable so I reported it as a bug. **Exact steps for others to reproduce the error** As a test I duplicated the default cube and moved it so the two cubes intersect. I then joined the cubes into one object. I set the subsurface method to 'random walk' and the subsurface slider to '1'. Cycles is used and I added a simple Area light above the cubes to see it better. [Based on the default startup or an attached .blend file (as simple as possible)] Attached is the quick test scene with the cubes and a render comparison between cycles in blender and the SSS random walk 2 in maya with arnold (the one with the black edges around the muscles is done with blender/cycles and the clean one is done with maya/arnold) ![Anatomystudy_v010.PNG](https://archive.blender.org/developer/F8974813/Anatomystudy_v010.PNG) ![Anatomystudy_v011.PNG](https://archive.blender.org/developer/F8974812/Anatomystudy_v011.PNG) [SSS_blackArtifacts_test.blend](https://archive.blender.org/developer/F8974816/SSS_blackArtifacts_test.blend)

Fynn Große-Bley commented

2020-10-10 15:12:13 +02:00

Added subscriber: @FynnGB

blender-admin commented

2020-10-10 15:12:13 +02:00

#85202 was marked as duplicate of this issue

Richard Antalik commented

2020-10-13 19:07:14 +02:00

Added subscribers: @brecht, @iss

Richard Antalik commented

2020-10-13 19:07:14 +02:00

I think that this has not much in common with #56914. Not sure though if what @brecht said applies to objects or "mesh groups" like in this case.

Brecht Van Lommel commented

2020-10-13 19:14:06 +02:00

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

Brecht Van Lommel closed this issue

2020-10-13 19:14:06 +02:00

Brecht Van Lommel self-assigned this 2020-10-13 19:14:06 +02:00

Brecht Van Lommel commented

2020-10-13 19:14:06 +02:00

From the docs:

Random Walk

Provides the most accurate results for thin and curved objects. This comes at the cost of increased render time or noise for more dense media like skin, but also better geometry detail preservation. Random Walk uses true volumetric scattering inside the mesh, which means that it works best for closed meshes. Overlapping faces and holes in the mesh can cause problems.

The description could perhaps be improved, but the point is that there must be a clear inside/outside for volumetric scattering, and with overlapping cubes as in the example file that is not the case.

From the docs: > Random Walk > > Provides the most accurate results for thin and curved objects. This comes at the cost of increased render time or noise for more dense media like skin, but also better geometry detail preservation. Random Walk uses true volumetric scattering inside the mesh, which means that it works best for closed meshes. Overlapping faces and holes in the mesh can cause problems. The description could perhaps be improved, but the point is that there must be a clear inside/outside for volumetric scattering, and with overlapping cubes as in the example file that is not the case.

Fynn Große-Bley commented

2020-10-13 20:33:58 +02:00

thanks for the replies! @brecht Should I post it as a feature request (as mentioned in the other task)? Or is this request already posted?
Thanks a lot!

thanks for the replies! @brecht Should I post it as a feature request (as mentioned in the other task)? Or is this request already posted? Thanks a lot!

Robert Guetzkow commented

2021-01-29 18:16:35 +01:00

Added subscribers: @Joe_W, @DarkKnight

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SSS Shader - Black artifacts with intersecting geometry within the same object #81602