UVs stretching in Blender 2.80

Hi guys,

I am having serious issues with UV stretching in Blender 2.80. I started having problems with unwrapping complex geometry to texture in Substance Painter, so I thought I’d try it with a simpler example: a simple barrel, 8 sided extruded circle; unwrapping works ok with a simple vertical seam at the back, there is no UV stretching at all. But as soon as I start creating the barrel’s ribs, the UVs fall apart: stretching start showing (see screenshot).

How can I correct this UV stretching? As soon as there is a little modeling involved, the UVs appear to stretch. I’ve tried everything I could think of: creating seams to isolate the ribs, avoiding N-gons, tris, interior faces, poles (checked with mesh lint), removing all doubles, and making sure the normals were pointing in the right direction. Am I missing something?

Please, can anybody help; without proper UVs, I cannot proceed forward with the project.

Thanks in advance.

If you move geometry after creating UVs, you are bound to create stretching, this is absolutely normal. There are limited number of cases where corrective action is applied to UVs during modelling (i.e. edge slide). So you either need to unwrap anew, or correct the UVs after making changes to mesh proportions.

But all the transforms were applied prior to unwrapping.

It doesn’t matter (in this case). You’ve unwrapped the barrel without ribs, then added ribs, correct? UVs can’t and don’t mimic the changes in topology or shape (barring a few cases like cutting loops or just sliding edges/vertices around, deleting faces). You’ve added some edge loops for ribs - that’s fine, the new UV faces were created accordingly. But then you pulled some of those edges inside the barrel, thereby creating more surface area on the mesh, but the UVs remained in place, hence the stretching.

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Hi Stan_Pancakes,

Thank you for your fast response. I’m not sure I follow you. I did unwrap again after creating the ribs, and the result is the screenshot I posted. Would you mind specifying how you’d resolve the issue?

Thanks in Advance. Kind Regards.

Ah, OK, it’s different then. With this barrel model the auto-unwraps such as Unwrap or Cylinder projection might not do the best of jobs in keeping proportions. With just two ribs to worry about, I’d simply scale the relevant UVs in the UV editor. But if there were more, or I didn’t have the UVs at all, I’d Unwrap just one big quad from the side, then select the rest of the faces (except the top and bottom if you have them), keeping the unwrapped face active, and do the Unwrap -> Follow Active Quads. It’s awesome for such regular geometry. Top and bottom will probably be fine with just the Unwrap. Then I’d select all the UVs, average island scale and pack them (these are options found in the UV menu of the UV editor).
There will still be some stretching (because those inset faces are no longer rectangular, but the UVs will be), but that’s usually unavoidable for any complex shape.
With more irregular shapes, some manual editing in the UV editor is inevitable.

Hi Stan_Pancakes,

Thank you very much for your answer; I didn’t know the size of the UVs mattered that much. I will certainly try that, and this Follow Active quad seems like an amazing solution. So much to learn!

Thank you for helping in the way.

Sept

Hi Stan_Pancake,

I just wanted to let you know the problem’s solved! Your comment that a little stretching is perfectly acceptable, put me on the track.

The problem was with the display of the built-in texture checker pattern I had loaded in the viewport, and not with the UVs; for some reason, the texture was mapped not only stretched but quite distorted in the viewport; didn’t seem related to the minor stretching in UVs (at most pale blue, without ever reaching the green). So I changed the parametric texture for an actual PNG and everything worked instantly, just unwrapping with a single seam at the back.

I can hardly see the mild stretching in Material Preview mode, or in Render mode! I suspect the unwrapping was correct all the way along, and it was the weird display of the parametric checker in the viewport led me to blame the UVs.

I wanted to thank you for all your advice and knowledge; it was all relevant and I learned a lot about UV unwrapping in the process. We can consider this issue closed

Kind Regards.

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