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Old 24th February 2019, 10:14 PM   #1
stitlown
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Question Degenerate UVs

May or maynot be a bug.

I have a .ac file that reports 5 or so degenerate UV surfaces, but as far as I can see the surfaces are not degenerate. They do however have 3 vertices in a straight line.

FWIW, there were (now deleted) a bunch of surfaces in this file that I would have called degenerate but which were not picked up by "select degenerate surfaces".

.ac file attached
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Old 26th February 2019, 02:25 PM   #2
Andy
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Default Re: Degenerate UVs

Please email me the file and I'll take a look.
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Old 26th February 2019, 07:21 PM   #3
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Default Re: Degenerate UVs

Done. Cheers. Lx
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Old 27th February 2019, 09:41 AM   #4
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Default Re: Degenerate UVs

OK - here's just one of the surfaces that is causing a problem.

Although it looks like a triangle, it's actually a quad. I have moved some vertices to show this. When this is triangulated (all polygons are ultimately turned to triangles before rendering), the top three vertices create a triangle with three vertices in a row - i.e. a triangle with no surface area, and therefore impossible to UV map correctly.


The solution here is to select the upper mid vertex and the lower vertex and then use Vertex->Slice-surface to split the quad into two triangles - shown in red/orange in the final picture.


So - degenerate UV detection is working but it was hard to spot what was causing it.
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Old 27th February 2019, 09:33 PM   #5
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Default Re: Degenerate UVs

Ok. Got it, thanks. I had seen the three vertices in a row - so now I know to hunt them down. Cheers, Lx
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Old 26th May 2020, 07:09 AM   #6
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Default Re: Degenerate UVs

Andy, are you aware "Sculptly Extrude" generates degernerate UVs (or more specifically, generates no UVs at all.

I would have expected that it was possible to capture the UVs of the downstream edges when scultply extruding.

My example is a cylinder primative I'm trying to make into a pole. The primative itself is just one segment long so one technique is to scultply extrude it into the pole I need, but that then creates a whole new UV painting challenge.

Any ideas? BTW, hope you are safe and cosy at home during the COVID crisis. Cheers, Lx

Also, are you aware sculptly extruding leaves unattached vertices. For example, if you take a primative 16 segment cylinder, it will have 2x16+2 vertices and 3x16 surfaces. If you scultply extrude one end, you'd expect to get 3x16+2 vertices and 4x16 surfaces, but the result is 3x16+3 vertices and 4x16 surfaces. There is a redundant central vertex left at the site of the extruded-from surface. Lx

Last edited by stitlown; 26th May 2020 at 07:20 AM.
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Old 27th May 2020, 06:25 AM   #7
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Default Re: Degenerate UVs

The plugins is third-party but I just tried it and Sculpty-extrude gave the correct results.


You need to make sure you start with one of the provided primitives, and then using sculpty-extrude will do its best to preserve the UV map.



The Second Life primitives are in the object-library, which by default should point to the model folder within the AC3D install folder. (Note (BUG) the menu File->Object-library is currently incorrectly overwritten by "Save <filename>" if you save a file - that is if you've not replace the tcl file).


In the secondlife folder you'll see a cylinder, sphere and cube designed with UV maps ready for Second Life.


I'm interested to know - are people still using Sculpties in SL? I thought everything would move to meshes, after support was added.


(and thanks - I'm fine - cheers!)
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Old 27th May 2020, 09:11 AM   #8
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Default Re: Degenerate UVs

Maybe my mistake - I've been using it to extrude any old object. Seemed a useful technique. Had not even noticed it was sculpty, not sculptly.
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Old 27th May 2020, 09:28 AM   #9
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Default Re: Degenerate UVs

Experiment working with the supplied objects - that's the way to go. The UV mapping has to be very specific for an object to work as a sculpty - very hard to do from scratch.
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Old 27th May 2020, 07:24 PM   #10
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Default Re: Degenerate UVs

<Thumbs up>
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