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Vertex order not kept when section of object rotated.
Closed, InvalidPublic

Description

System Information
Operating system: win 10
Graphics card: 1050

Blender Version
Broken: 2.8 16 June

Not sure if this is bug or feature. Apologies if feature :)

I have a pair of objects ( actually legs, but could be anything..)

to animate them we tween between legs left and legs right.. they have different positions. For this to work, we must have the vertex indices unchanged. But, when we make a duplicate and move the legs, the vertex order is not the same.

It feels that this could be easily fixed with a simple setting.. but I'm not a blendev

The object is actually 3 meshes grouped. ( legs, feet, shoes)

Details

Type
Bug

Event Timeline

Please include exact steps for reproducing this problem (ideally starting from the default scene, or upload a blend file with a simple scene demonstrating the problem).

In the meantime, you might want to investigate the element sorting operations (3d view header -> Mesh menu -> Sort Elements... submenu).

Bastien Montagne (mont29) triaged this task as Needs Information from User priority.

Indeed, Please always attach a small and simple .blend file to help reproducing the issue, always saves us a tremendous of time.

OK.. I have tried this with a small ans simple object and it works fine.

However, I attach the simplest object I can to demonstrate the problem.

  1. Open legs.blend
  2. duplicate the LegsRest object twice by copy and paste in the Outliner.
  3. select the vertices below the knee and rotate them so the leg is straight.
  4. export the 3 objects to wavefront obj. triangulate/keep vertex order.
  5. examine the obj file with text editor. vertex order is different between LegsRest and duplicated objects.

Sorry I can't get any simpler than this guys.

Bastien Montagne (mont29) claimed this task.

Pffff… Took me ages to understand what was happening here… You have AutoMerge ON in your 3D View's Tool Options (right panels). So every time you edit your mesh (rotate, scale, etc. etc.), you change amount of tris and hence its topology.

I apologise.. making the blend file extracted from my model I forgot the turn that off. :-(

BUT !!!!!!!!!!

Did you try it with Automerge off?

Do that and you will see the vertex order still gets munged.

Chris Wedgwood (OXO) reopened this task as Open.Jul 2 2019, 5:38 PM

No vorder is not changed, not at all. Your face do not match in text diffing because the indices of the normals change (since the vnors are not the same, which is expected, and OBJ 'compresses' vnors by not writing twice the same vector). The first two indices of the triplet vidx/uvidx/noidx remain unchanged, which demonstrates that vert order remains unchanged!