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Maniphest T87478

Eevee renders seam in generated noise, Cycles does not.
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Description

System Information
Operating system: Linux-4.15.0-141-generic-x86_64-with-glibc2.27 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.39

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-04-13 07:49, hash: rB30ee57be60b7
Worked: (newest version of Blender that worked as expected)

Short description of error
In this simple test model, Eevee renders a seam in the generated texture, Cycles does not.

Exact steps for others to reproduce the error
Open attached file.
Render.
Note seam in generated noise on left object (it has an extra loop cut).
Switch to Cycles.
Bump up sunlight to 400.
Render. No seam in texture.

Bug Report Eevee 003.blend870 KBDownload

Event Timeline

Robert Townsend (rtownsend) created this task.Apr 14 2021, 4:42 AM
Germano Cavalcante (mano-wii) added a subscriber: Germano Cavalcante (mano-wii).Apr 16 2021, 9:51 PM

I'm not sure what's going on but it seems to be related to the "Show Blackface" option.

Robert Townsend (rtownsend) added a comment.Apr 17 2021, 5:03 PM

Turning on 'Backface Culling' does change the behavior, and removes the seam. Looks like a good clue.

Pratik Borhade (PratikPB2123) added a subscriber: Pratik Borhade (PratikPB2123).Jun 24 2021, 11:50 AM

@Robert Townsend (rtownsend) , it seems Germano's message helped you in some way. If you think this is not a bug then can we close the task? :)

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Needs Information from User.Jun 24 2021, 7:06 PM
Robert Townsend (rtownsend) added a comment.Jun 26 2021, 5:02 AM

When I filed this report, I was not completely sure it was a bug. I'm still not. It does not seem to work correctly, but I'm not versed enough in Eevee vs Cycles to know. It's seems weird to me that checking 'Backface Culling' in the material settings in this particular example fixes the problem, but isn't usually required for other objects. It also seems weird that there's a case where Eevee would render a seam, and Cycles would not.

I've followed Blender for a long time, but I wouldn't call myself a power user. Maybe run it by Clement Foucault? Ton? Let me know if I can help in any way.

Richard Antalik (ISS) closed this task as Archived.Jul 6 2021, 8:15 AM
Richard Antalik (ISS) added a subscriber: Richard Antalik (ISS).

Seems this is cause by Show Backside option

This seems to be known issue - see https://docs.blender.org/manual/en/latest/render/eevee/materials/settings.html#sorting-problem

If enabled, all transparent fragments will be rendered. If disabled, only the front-most surface fragments will be rendered. Disable this option to ensure correct appearance of transparency from any point of view. Then using Alpha Blending this option should be disabled because with Alpha Blending, the order in which triangles are sorted is important.

Closing since this issue happens as documentation predicts.