Subdivision modifier's Subdivide UV not working correctly with overlapping UV islands vertices. #44535

New Issue

Jaroslav Novotny · 2015-04-28T13:35:19+02:00

Jaroslav Novotny commented

2015-04-28 13:35:19 +02:00

System Information
Win 7 64bit GTX780

Blender Version
Broken: v.2.74 hash: 000dfc0
Worked: probably none

Short description of error
When mesh is Catmull-Clark subdivided with modifier and the UVs too (Subdivide UVs checked), vertices that are unwrapped to multiple UV islands are not correctly subdivided when these overlap in UV space. They are single vertex in geometry but they are not connected in UVs.

Exact steps for others to reproduce the error
Blend: subdivision_UV_bug.blend

Object Layer 1: A more practical example when mirror-tiling same portion of texture over a surface:
There is 6 polygon strip unwrapped into 2 islands, one island is mirrored. The islands are offsetted to show correct behavior. Grab the right island and move it -1 in X direction to overlap them. You will see stretching on the seam as blender thinks the vertices are connected when they overlap.

Object Layer 2: A more clear example whats going on.
A similar polygon, the islands overlap on 1 UV vertex, you can see the distortion in texture as the UVs were subdivided there the wrong way. Move the islands apart and the distortion is gone.

**System Information** Win 7 64bit GTX780 **Blender Version** Broken: v.2.74 hash: 000dfc0 Worked: probably none **Short description of error** When mesh is Catmull-Clark subdivided with modifier and the UVs too (Subdivide UVs checked), vertices that are unwrapped to multiple UV islands are not correctly subdivided when these overlap in UV space. They are single vertex in geometry but they are not connected in UVs. **Exact steps for others to reproduce the error** Blend: [subdivision_UV_bug.blend](https://archive.blender.org/developer/F167608/subdivision_UV_bug.blend) Object Layer 1: A more practical example when mirror-tiling same portion of texture over a surface: There is 6 polygon strip unwrapped into 2 islands, one island is mirrored. The islands are offsetted to show correct behavior. Grab the right island and move it -1 in X direction to overlap them. You will see stretching on the seam as blender thinks the vertices are connected when they overlap. Object Layer 2: A more clear example whats going on. A similar polygon, the islands overlap on 1 UV vertex, you can see the distortion in texture as the UVs were subdivided there the wrong way. Move the islands apart and the distortion is gone.

Jaroslav Novotny commented

2015-04-28 13:35:20 +02:00

Changed status to: 'Open'

Jaroslav Novotny commented

2015-04-28 13:35:20 +02:00

Added subscriber: @jerryno

perfection cat commented

2015-05-01 05:44:02 +02:00

Added subscriber: @sindra1961

perfection cat commented

2015-05-01 05:44:02 +02:00

This comment was removed by @sindra1961

*This comment was removed by @sindra1961*

Sergey Sharybin was assigned by Bastien Montagne

2015-05-01 18:49:59 +02:00

Bastien Montagne commented

2015-05-01 18:49:59 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2015-05-01 18:49:59 +02:00

Can confirm the issue… Assigning to Sergey for final decision, but imho we should just handle this as known limitation and wait for imminent new subdiv code to check whether it is still relevant or not?

Brecht Van Lommel commented

2015-05-01 19:56:36 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2015-05-01 19:56:36 +02:00

This seems a little tricky, you want this to be considered as two separate islands, while the subdivide UV code interprets it as a single island that has been "folded" in the middle. I suspect OpenSubdiv will suffer from the same issue, but it might indeed be good to test that before spending time on this.

perfection cat commented

2015-05-02 02:31:37 +02:00

Removed subscriber: @sindra1961

Sergey Sharybin commented

2015-05-06 13:01:38 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2015-05-06 13:01:38 +02:00

Sergey Sharybin commented

2015-05-06 13:01:38 +02:00

OpenSubdiv currently tries to match old UV subdivision as close as possible due to compatibility reasons. If we decide it'll make more sense to treat those as separate islands we can break compatibility and support this.

But i don't really consider this a bug, it's just how blender works, So thanks for the report, but archiving it now.

OpenSubdiv currently tries to match old UV subdivision as close as possible due to compatibility reasons. If we decide it'll make more sense to treat those as separate islands we can break compatibility and support this. But i don't really consider this a bug, it's just how blender works, So thanks for the report, but archiving it now.

Jaroslav Novotny commented

2015-05-06 18:37:07 +02:00

This comment was removed by @jerryno

*This comment was removed by @jerryno*

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Subdivision modifier's Subdivide UV not working correctly with overlapping UV islands vertices. #44535