Subdividing edges causes unwrap to "ignore" edge seam #31901

New Issue

Jerome Britton · 2012-06-22T19:37:06+02:00

Jerome Britton commented

2012-06-22 19:37:06 +02:00

%%%Windows Vista 64-bit
GeForce 9600 GT
Blender 2.63 R46461
Blender 2.63 R48065

RECREATION
From empty scene:
Add mesh/plane
Edit mode
Subdivide (1-cut)
Select the newly created edges
Mark edges as seams
Select the three parallel edges on one half of the plane (ex. on the left half, the three horizontal edges)
Subdivide those edges (1-cut) resulting in a plane with 6 faces
Select all
Unwrap

RESULT
This results in an unwrapped mesh with two quarters of the plane connected through the center vertex.

NOTE: It does NOT matter when you mark the seams. You can wait and mark them after the second subdivide and still re-create the issue.

DISCOVERY
Found after reworking topology on a moderately complex mesh. Used subdivide to create new vertices in a sub-region.%%%

%%%Windows Vista 64-bit GeForce 9600 GT Blender 2.63 R46461 Blender 2.63 R48065 RECREATION From empty scene: Add mesh/plane Edit mode Subdivide (1-cut) Select the newly created edges Mark edges as seams Select the three parallel edges on one half of the plane (ex. on the left half, the three horizontal edges) Subdivide those edges (1-cut) resulting in a plane with 6 faces Select all Unwrap RESULT This results in an unwrapped mesh with two quarters of the plane connected through the center vertex. NOTE: It does NOT matter when you mark the seams. You can wait and mark them after the second subdivide and still re-create the issue. DISCOVERY Found after reworking topology on a moderately complex mesh. Used subdivide to create new vertices in a sub-region.%%%

Jerome Britton commented

2012-06-22 19:37:06 +02:00

Changed status to: 'Open'

Sergey Sharybin commented

2012-06-23 11:42:31 +02:00

%%%Antony, could you please glance at this issue? Thanks! :)%%%

Antonis Ryakiotakis commented

2012-06-23 23:51:26 +02:00

%%%The issue, quite simply is the way our UV system works. The notion of UV islands is non persistent. Internally we have only a colection of MTFaces, NOT a collection of islands of MTFaces. What happens is that when you select a uv, it will automatically select any adjacent uvs whose vertex is the same, independently of the 'island' you thought they may be part of (Remember, there's no such thing as islands internally). To solve this properly we need to redesign the uv system to accomodate islands unfortunately (for which I have a few ideas). Other than that, as a workaround, I would try this:

Unwrap
Pack islands and increase the margin
Reunwrap

The second unwrap remembers the margin setting and it will separate the islands, so selecting the uvs will behave correctly.

Sergey, should I close or mark as TODO?%%%

%%%The issue, quite simply is the way our UV system works. The notion of UV islands is non persistent. Internally we have only a colection of MTFaces, NOT a collection of islands of MTFaces. What happens is that when you select a uv, it will automatically select any adjacent uvs whose vertex is the same, independently of the 'island' you thought they may be part of (Remember, there's no such thing as islands internally). To solve this properly we need to redesign the uv system to accomodate islands unfortunately (for which I have a few ideas). Other than that, as a workaround, I would try this: - Unwrap - Pack islands and increase the margin - Reunwrap The second unwrap remembers the margin setting and it will separate the islands, so selecting the uvs will behave correctly. Sergey, should I close or mark as TODO?%%%

Antonis Ryakiotakis commented

2012-06-23 23:55:07 +02:00

%%%Clarification, when selecting you will get coincident not adjacent uvs that share the same vertex.%%%

Jerome Britton commented

2012-06-24 01:27:03 +02:00

%%%Thanks for the work-around. Great job!
So, if unwrap had placed those islands in different places on the map, there wouldn't have been a problem (or at least not the same problem)? That explains why the connected islands seemed to change as I tried to fix the problem by changing the mesh. It was very confusing.

Glad you guys are around! :)
Thanks again.%%%

%%%Thanks for the work-around. Great job! So, if unwrap had placed those islands in different places on the map, there wouldn't have been a problem (or at least not the same problem)? That explains why the connected islands seemed to change as I tried to fix the problem by changing the mesh. It was very confusing. Glad you guys are around! :) Thanks again.%%%

Antonis Ryakiotakis commented

2012-06-24 02:11:33 +02:00

%%%Exactly, it was a different vertex sharing uvs in the same space for a different unwrap.%%%

Antonis Ryakiotakis commented

2012-06-24 02:12:43 +02:00

%%%Marking as TODO%%%

Antonis Ryakiotakis commented

2012-06-24 02:12:44 +02:00

Changed status from 'Open' to: 'Archived'

Antonis Ryakiotakis closed this issue

2012-06-24 02:12:44 +02:00

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Subdividing edges causes unwrap to "ignore" edge seam #31901