Maniphest T81298

Incorrect rendering in cycles with skin modifier
Closed, Duplicate
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Assigned To
None
Authored By
Sekhar Ravinutala (sekhar)
Sep 29 2020, 3:43 PM
Tags
  • BF Blender
  • Cycles
Subscribers
Aaron Carlisle (Blendify)
Brecht Van Lommel (brecht)
Germano Cavalcante (mano-wii)
Jean Da Costa (jeacom256)
Richard Antalik (ISS)
Sekhar Ravinutala (sekhar)

Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2080 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.38

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-29 00:11, hash: rBb150071ece73
Worked: The last one I tried (2.90.1) also had this issue

Short description of error
Object with skin modifier isn't getting rendered correctly in cycles, both with CPU and GPU. Eevee OK.

Exact steps for others to reproduce the error
Open blender and apply skin modifier on the default cube. Render in cycles with CPU, you will wrong render. Same problem with GPU (I tried OptiX). Now try with NR (I tried OptiX), you again get a wrong render, except with different errors. See the attached files for my results.

skin.blend755 KBDownload

Event Timeline

Sekhar Ravinutala (sekhar) created this task.Sep 29 2020, 3:43 PM
Germano Cavalcante (mano-wii) added a project: Cycles.Oct 6 2020, 8:24 PM
Germano Cavalcante (mano-wii) added a subscriber: Germano Cavalcante (mano-wii).

There’s a difference between the way ngon normals are handled in cycles compared to Eevee or Workbench.
I don't know if this limitation is described anywhere, but it has always been that way.

I don't think it's a bug.

Jean Da Costa (jeacom256) added a subscriber: Jean Da Costa (jeacom256).Oct 6 2020, 8:32 PM

I suspect adding a triangulate modifier should fix this discrepancy.

Richard Antalik (ISS) added subscribers: Aaron Carlisle (Blendify), Richard Antalik (ISS).Oct 7 2020, 2:43 PM

As @Germano Cavalcante (mano-wii) said, the issue here is n-gons - the face is non-planar and it is triangulated so it can be rendered "realistically".

See https://blenderartists.org/t/modeling-rendering-issue/604780 for example

I don't know if we can fit this information nicely into documentation. @Aaron Carlisle (Blendify) what do you think?

Brecht Van Lommel (brecht) closed this task as a duplicate of T48937: different Skin Modifier outputs for same mesh.Oct 7 2020, 2:49 PM
Brecht Van Lommel (brecht) added a subscriber: Brecht Van Lommel (brecht).

This is a bug in the skin modifier, it randomly gives different outputs unrelated to the specific device or tesselation that happens after.