blender uv stretch with area show full red (on large scale mesh) #93084

Closed
opened 2021-11-14 23:37:20 +01:00 by nik · 15 comments

System Information
Operating system: Win 10
Graphics card: RTX 3090

Blender Version
Broken: 2.93.5

blender uv stretch with area show full red.

image.png

This how its should be:
image.png

File:
ShipsPartsTurretsTest.blend

To reproduce try open file and display stretch with area.

**System Information** Operating system: Win 10 Graphics card: RTX 3090 **Blender Version** Broken: 2.93.5 blender uv stretch with area show full red. ![image.png](https://archive.blender.org/developer/F11804444/image.png) This how its should be: ![image.png](https://archive.blender.org/developer/F11804459/image.png) File: [ShipsPartsTurretsTest.blend](https://archive.blender.org/developer/F11804476/ShipsPartsTurretsTest.blend) To reproduce try open file and display stretch with area.
Author

Added subscriber: @samrrr

Added subscriber: @samrrr
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Added subscriber: @lichtwerk

Added subscriber: @lichtwerk
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Changed status from 'Needs Triage' to: 'Confirmed'

Changed status from 'Needs Triage' to: 'Confirmed'
Member

Assume this has to do with unit scale.
With a unit scale of 1 this is almost 1.4km wide
Bringing this back to 1/100th of the scale then behaves better:
ShipsPartsTurretsTest_unitscale.blend

I guess this just results in too high numbers.

related commit:

But of course it should not mess with the stretch like that, so confirming for now (I assume this should just take scene's Unit Scale into account?)

Assume this has to do with unit scale. With a unit scale of 1 this is almost 1.4km wide Bringing this back to 1/100th of the scale then behaves better: [ShipsPartsTurretsTest_unitscale.blend](https://archive.blender.org/developer/F11807827/ShipsPartsTurretsTest_unitscale.blend) I guess this just results in too high numbers. related commit: - 4440739699 But of course it should not mess with the stretch like that, so confirming for now (I assume this should just take scene's `Unit Scale` into account?)
Philipp Oeser changed title from blender uv stretch with area show full red. to blender uv stretch with area show full red (on large scale mesh) 2021-11-15 10:30:43 +01:00
Author

UE work correct only with scale 0.01. I cant change its.

UE work correct only with scale 0.01. I cant change its.

Added subscriber: @JacRossiter

Added subscriber: @JacRossiter

Hello. I've also been having the same issue. The uv stretch shows incorrectly when objects are too large. I don't want to rescale the object though as it will create issues when dealing with other programs. This seems like an issue with how blender percieves uv stretching as opposed to a user error.

Hello. I've also been having the same issue. The uv stretch shows incorrectly when objects are too large. I don't want to rescale the object though as it will create issues when dealing with other programs. This seems like an issue with how blender percieves uv stretching as opposed to a user error.
Philipp Oeser self-assigned this 2022-08-24 14:31:33 +02:00
Member

Think I got a fix

Think I got a fix
Member

Hrmf, while I have a patch the resolves the issue on large meshes, I just noticed the stretch overlay is more fundamentally broken (I think).

The overall issue is that we have the issue that changing a single UV will affect the stretch of all faces (which should not happen imho).
So the fix will need to go a bit deeper even (the whole problem is that ratios for faces are calculated from total UV area [which of course changes if you change any participating UV...]

Not sure yet if I will report this separately, but here it is in action:
#93084.webm

Can still post my patch which solves the following:

  • atm we store ratios between the face area and the UV area (this can get 0.0 due to floating point issues on large face areas)
  • the patch first calculates a ratio of a face area in relation to all other faces, then stores a ratio of a uv area in relation to all other uv areas, then divides these rations (thus avoiding the issue mentioned above)
Hrmf, while I have a patch the resolves the issue on large meshes, I just noticed the stretch overlay is more fundamentally broken (I think). The overall issue is that we have the issue that changing a single UV will affect the stretch of all faces (which should not happen imho). So the fix will need to go a bit deeper even (the whole problem is that ratios for faces are calculated from total UV area [which of course changes if you change any participating UV...] Not sure yet if I will report this separately, but here it is in action: [#93084.webm](https://archive.blender.org/developer/F13418377/T93084.webm) Can still post my patch which solves the following: - atm we store ratios between the face area and the UV area (this can get 0.0 due to floating point issues on large face areas) - the patch first calculates a ratio of a face area in relation to all other faces, then stores a ratio of a uv area in relation to all other uv areas, then divides these rations (thus avoiding the issue mentioned above)

hmm, interestesting. Sounds a bit more tricky than initial though. I appreciate your work on this though so far. My fingers are crossed a solution can be found. One thing that's interesting is that average island still works fine with large meshes so perhaps that operator has a different way to calculate relative scale. Just a though :) Thanks again

hmm, interestesting. Sounds a bit more tricky than initial though. I appreciate your work on this though so far. My fingers are crossed a solution can be found. One thing that's interesting is that average island still works fine with large meshes so perhaps that operator has a different way to calculate relative scale. Just a though :) Thanks again
Member

Added subscriber: @ideasman42

Added subscriber: @ideasman42
Member

Talked with @ideasman42 about that video I posted (but that is apparently by design atm.) and is also a lot less noticable on usual production meshes (with more polygons etc.)
So while this could also be improved, it is not going to be part of handling this bug report.

reg. the Average Islands Scale operator: that uses the UV parametrizer internally (afaict it uses doubles internally, this would be another possibility to look at), but that would involve a bigger rewrite of the area (and I havent checked on other implications such as performance with doing that).

So for now, will post my original patch (this should solve the large scale mesh issue nicely as well), lets see what review for that gives us.

Talked with @ideasman42 about that video I posted (but that is apparently by design atm.) and is also a lot less noticable on usual production meshes (with more polygons etc.) So while this could also be improved, it is not going to be part of handling this bug report. reg. the `Average Islands Scale` operator: that uses the UV parametrizer internally (afaict it uses doubles internally, this would be another possibility to look at), but that would involve a bigger rewrite of the area (and I havent checked on other implications such as performance with doing that). So for now, will post my original patch (this should solve the large scale mesh issue nicely as well), lets see what review for that gives us.

Okay great, thanks for the update! Your patch will be invaluable for a lot of meshes. :)

Okay great, thanks for the update! Your patch will be invaluable for a lot of meshes. :)

This issue was referenced by f20d0de3b7

This issue was referenced by f20d0de3b7b4678257669d558a3ebb40115939c7
Member

Changed status from 'Confirmed' to: 'Resolved'

Changed status from 'Confirmed' to: 'Resolved'
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Reference: blender/blender#93084
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