subdivision surface with UV smooth "keep corners" destroys UV/seams #84419

New Issue

Stefan Mayr · 2021-01-05T17:37:05+01:00

Stefan Mayr commented

2021-01-05 17:37:05 +01:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.89

Blender Version
Broken: version: 2.92.0 Alpha, branch: master, commit date: 2020-12-26 22:50, hash: 7916c59304
Worked: (newest version of Blender that worked as expected)

Short description of error

when applying a subdivision surface modifier with UV smoothing set to "keep corners" it rips the UVs and therefore creates additional seems when hitting "seams from islands". This seems to be only happening with the "keep corners" option, and when the original mesh (before applying the subdiv modifier is appied) is not super low res. The UV islands look visually fine, however has vertices ripped apart. It can be solved by merging by distance with a very low threshold. I tried in official 2.91 release and having the same result there.

Exact steps for others to reproduce the error

apply a subivision modifier with a level 2 to the default cube (already set up in provided scene)
in UV editor select all and hit "seams from islands"
apply a new subdivision modifier with any level to the cube and UV smoothing set to "keep corners" (already set up in provided scene, but not applied yet)
in edit mode delete all seams
in UV editor select all and hit "seams from islands"
additional seams have been added based on where the vertices in UV got ripped apart

cube_UV_test.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.89 **Blender Version** Broken: version: 2.92.0 Alpha, branch: master, commit date: 2020-12-26 22:50, hash: `7916c59304` Worked: (newest version of Blender that worked as expected) **Short description of error** when applying a subdivision surface modifier with UV smoothing set to "keep corners" it rips the UVs and therefore creates additional seems when hitting "seams from islands". This seems to be only happening with the "keep corners" option, and when the original mesh (before applying the subdiv modifier is appied) is not super low res. The UV islands look visually fine, however has vertices ripped apart. It can be solved by merging by distance with a very low threshold. I tried in official 2.91 release and having the same result there. **Exact steps for others to reproduce the error** - apply a subivision modifier with a level 2 to the default cube (already set up in provided scene) - in UV editor select all and hit "seams from islands" - apply a new subdivision modifier with any level to the cube and UV smoothing set to "keep corners" (already set up in provided scene, but not applied yet) - in edit mode delete all seams - in UV editor select all and hit "seams from islands" - additional seams have been added based on where the vertices in UV got ripped apart [cube_UV_test.blend](https://archive.blender.org/developer/F9551568/cube_UV_test.blend)

Stefan Mayr commented

2021-01-05 17:37:05 +01:00

Added subscriber: @Dabreiss

Germano Cavalcante commented

2021-01-06 19:46:59 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2021-01-06 19:46:59 +01:00

This is a side effect of the same problem described in #81065
This "interpolation" of UVs with the subdvision modifier is not perfect and can create small gaps between the new UVs generated.
So some UVs are disconnected.

This is a side effect of the same problem described in [#81065 ](https://developer.blender.org/T81065) This "interpolation" of UVs with the subdvision modifier is not perfect and can create small gaps between the new UVs generated. So some UVs are disconnected.

Germano Cavalcante commented

2021-01-06 19:47:10 +01:00

Closed as duplicate of #81065

Germano Cavalcante closed this issue

2021-01-06 19:47:10 +01:00

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subdivision surface with UV smooth "keep corners" destroys UV/seams #84419