unsubdivide of Multires bug #85792

New Issue

yongchang · 2021-02-19T15:33:20+01:00

yongchang commented

2021-02-19 15:33:20 +01:00

Blender Version2.91

I try to use unsubdivide of Multires function in blender ,but the result is error.So I test in Zbrush with same modle, it work rightly.

The thing is,I want sculpt with tank top with no thickness,and add thick ness at last.So I first sculpt with Multires (3 level subdivide),and apply it,and I loop cut the edge with 7 loop cut.After that I add Multires,and use unsubdivide,the result go wrong.

I use the same modle in Zbrush,it work rightly.unsubdivide error.zip

**Blender Version**2.91 I try to use unsubdivide of Multires function in blender ,but the result is error.So I test in Zbrush with same modle, it work rightly. The thing is,I want sculpt with tank top with no thickness,and add thick ness at last.So I first sculpt with Multires (3 level subdivide),and apply it,and I loop cut the edge with 7 loop cut.After that I add Multires,and use unsubdivide,the result go wrong. I use the same modle in Zbrush,it work rightly.[unsubdivide error.zip](https://archive.blender.org/developer/F9817835/unsubdivide_error.zip)

yongchang commented

2021-02-19 15:33:20 +01:00

Added subscriber: @yongchang27

Pablo Dobarro commented

2021-02-19 18:32:38 +01:00

Added subscriber: @PabloDobarro

Pablo Dobarro commented

2021-02-19 18:32:38 +01:00

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

Pablo Dobarro commented

2021-02-19 18:32:38 +01:00

The different between the unsubdivide functionality of ZBrush and Blender is that ZBrush can only find solutions with quads and triangles in the base mesh, while Blender supports base meshes with ngons. For your particular mesh, two unsubdivide solutions are valid for creating an subdivisible base mesh (as you can see in that file, when subdividing the result of Blender's unsubdivide, the topology looks the same as unsubdivide_prepare version). Currently, Blender does have any heuristic to choose which base mesh solution is preferred (I also don't know if this is something that can be valid for all cases), so it creates the base mesh for the first valid solution it finds. In the future it may be possible to force unsubdivide to search for all possible solutions and choose the one that does not creates ngons in the base mesh if multiple valid solutions are available.

Anthony commented

2021-03-02 22:16:56 +01:00

Added subscriber: @PancakeZ

Anthony commented

2021-03-02 22:16:56 +01:00

multires unsubdivide BUG.blend
multires unsubdivide BUG.obj
@PabloDobarro I have a similar problem. I sculpted a pair of pants with multires but can not unsubdivide after applying the modifier.
I tried it in 2.91.2, 2.92 rc, and 2.93
It's weird because the multires is working before applying and adding a new multires to unsubdivide. I want to do this because the resulting shape of the unsubdivided lowest level is much better looking than the reshaped base. I need it for gametopology.

To reproduce the bug check the Blendfile and:

Open the file and apply the Multires on the "pants" object
After applying the Multires add a new fresh Multires and try "rebuilding subdivisions" or "unsubdivide"
Blender throws this error-message: "Not valid subdivisions found to rebuild a lower level"

Alternatively I will upload the exported obj of the pantmodel. For me it is the exact same issue. After importing the obj i try adding a multires and unsubdividing resulting in the same error message. No ngons, tris and all even grid-quads.

[multires unsubdivide BUG.blend](https://archive.blender.org/developer/F9861076/multires_unsubdivide_BUG.blend) [multires unsubdivide BUG.obj](https://archive.blender.org/developer/F9861077/multires_unsubdivide_BUG.obj) @PabloDobarro I have a similar problem. I sculpted a pair of pants with multires but can not unsubdivide after applying the modifier. I tried it in 2.91.2, 2.92 rc, and 2.93 It's weird because the multires is working before applying and adding a new multires to unsubdivide. I want to do this because the resulting shape of the unsubdivided lowest level is much better looking than the reshaped base. I need it for gametopology. To reproduce the bug check the Blendfile and: 1. Open the file and apply the Multires on the "pants" object 2. After applying the Multires add a new fresh Multires and try "rebuilding subdivisions" or "unsubdivide" 3. Blender throws this error-message: "Not valid subdivisions found to rebuild a lower level" Alternatively I will upload the exported obj of the pantmodel. For me it is the exact same issue. After importing the obj i try adding a multires and unsubdividing resulting in the same error message. No ngons, tris and all even grid-quads.

Pablo Dobarro commented

2021-03-03 01:09:07 +01:00

@PancakeZ That is a different issue. The problem in that case is that the geometry contains a loose vertex, so unsubdivide can't create a displacement grid for it and the operation fails. Unsubdivide does not work with with meshes with loose geometry.

@PancakeZ That is a different issue. The problem in that case is that the geometry contains a loose vertex, so unsubdivide can't create a displacement grid for it and the operation fails. Unsubdivide does not work with with meshes with loose geometry. ![Screenshot from 2021-03-03 01-06-35.png](https://archive.blender.org/developer/F9861363/Screenshot_from_2021-03-03_01-06-35.png)

Anthony commented

2021-03-03 14:13:01 +01:00

In #85792#1122985, @PabloDobarro wrote:
@PancakeZ That is a different issue. The problem in that case is that the geometry contains a loose vertex, so unsubdivide can't create a displacement grid for it and the operation fails. Unsubdivide does not work with with meshes with loose geometry.

@PabloDobarro Thank you very much! I will keep that in mind in the future to check for loose vertecies if that happens again!

> In #85792#1122985, @PabloDobarro wrote: > @PancakeZ That is a different issue. The problem in that case is that the geometry contains a loose vertex, so unsubdivide can't create a displacement grid for it and the operation fails. Unsubdivide does not work with with meshes with loose geometry. > ![Screenshot from 2021-03-03 01-06-35.png](https://archive.blender.org/developer/F9861363/Screenshot_from_2021-03-03_01-06-35.png) @PabloDobarro Thank you very much! I will keep that in mind in the future to check for loose vertecies if that happens again!

Philipp Oeser removed the

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unsubdivide of Multires bug #85792