automatic weights ignores loose parts #90340

New Issue

shannon zachow · 2021-07-31T20:29:50+02:00

shannon zachow commented

2021-07-31 20:29:50 +02:00

System Information
Operating system: Linux
Graphics card: RTX-2060

Blender Version
Broken: 2.93.2rc, 3.0.0alpha (built on 2021jul31), 2.92.0
Worked: ?

Short description of error
Automatic Weights ignores non-overlapping loose parts in mesh to be parented to Armature.

Exact steps for others to reproduce the error
Create a Mesh containing loose parts (islands).
Create an Armature.
ctrl-P Parent mesh to armature > with Automatic Weights
Pose Mode on Armature: move whole or bones, the loose parts are left in original position.

see attached .blend file.
test039_autoWeight.blend

system-info-2.93.2rc.txt

This is not a high-priority bug, but rather a short-coming. Trying to match weights by hand doesn't give very satisfactory results, as the loose parts drift in and out of proximity during posing, because my hand-weighting doesn't quite match auto-weights generated. Overlapping the islands totally solves it, but how is anyone supposed to diagnose that?
I report this in the hopes that it can be fixed someday, in order to save others the hours I spent trying to figure out what was going on.

Thank you for blender!!! :D

**System Information** Operating system: Linux Graphics card: RTX-2060 **Blender Version** Broken: 2.93.2rc, 3.0.0alpha (built on 2021jul31), 2.92.0 Worked: ? **Short description of error** Automatic Weights ignores non-overlapping loose parts in mesh to be parented to Armature. **Exact steps for others to reproduce the error** Create a Mesh containing loose parts (islands). Create an Armature. ctrl-P Parent mesh to armature > with Automatic Weights Pose Mode on Armature: move whole or bones, the loose parts are left in original position. see attached .blend file. [test039_autoWeight.blend](https://archive.blender.org/developer/F10250958/test039_autoWeight.blend) [system-info-2.93.2rc.txt](https://archive.blender.org/developer/F10250959/system-info-2.93.2rc.txt) This is not a high-priority bug, but rather a short-coming. Trying to match weights by hand doesn't give very satisfactory results, as the loose parts drift in and out of proximity during posing, because my hand-weighting doesn't quite match auto-weights generated. Overlapping the islands totally solves it, but how is anyone supposed to diagnose that? I report this in the hopes that it can be fixed someday, in order to save others the hours I spent trying to figure out what was going on. Thank you for blender!!! :D

shannon zachow commented

2021-07-31 20:29:50 +02:00

Added subscriber: @shannonz

Philipp Oeser commented

2021-08-03 10:53:36 +02:00

Added subscribers: @brecht, @lichtwerk

Philipp Oeser commented

2021-08-03 10:53:36 +02:00

This is essentially the same as #45493 (Bone Heat weighting: failed (due to none of the vertices in an island being visible to any bones)).

So if the bone heat algorithm cannot "see" any vertex in an island, the algo might fail, as soon as one vertex is visible (in this case here: overlapping) all is fine.

Here is the workaround (which is working fine in your file) and a more detailed explanation:

In #45493#322764, @brecht wrote:
A workaround is to split the mesh and then bind the weights. Enter editmode on the mesh, L linked select the body, P to separate into a separate mesh, compute the weights for the two meshes separately, and Ctrl + J join them again.

It seems there is some issue with the teeth where they are not visible to any bone, which is somehow messing things up.

In #45493#322765, @brecht wrote:
I think the problem is that the algorithm does not explicitly handle connected components separately. They are all handled in a single matrix, and that's usually fine. But if none of the vertices in a connected component are visible to any bones, then the matrix will not be invertible, and the solve will fail for all components.

The solution would be to detect such cases, and then disable visibility tests for such components, or somehow get the weights from nearby components. Switching the code to use BMesh instead of Mesh would make that easier.

Will merge this into #45493 though, thx reporting!

This is essentially the same as #45493 (Bone Heat weighting: failed (due to none of the vertices in an island being visible to any bones)). So if the bone heat algorithm cannot "see" any vertex in an island, the algo might fail, as soon as one vertex is visible (in this case here: overlapping) all is fine. Here is the workaround (which is working fine in your file) and a more detailed explanation: > In #45493#322764, @brecht wrote: > A workaround is to split the mesh and then bind the weights. Enter editmode on the mesh, `L` linked select the body, `P` to separate into a separate mesh, compute the weights for the two meshes separately, and `Ctrl + J` join them again. > > It seems there is some issue with the teeth where they are not visible to any bone, which is somehow messing things up. > In #45493#322765, @brecht wrote: > I think the problem is that the algorithm does not explicitly handle connected components separately. They are all handled in a single matrix, and that's usually fine. But if none of the vertices in a connected component are visible to any bones, then the matrix will not be invertible, and the solve will fail for all components. > > The solution would be to detect such cases, and then disable visibility tests for such components, or somehow get the weights from nearby components. Switching the code to use BMesh instead of Mesh would make that easier. Will merge this into #45493 though, thx reporting!

Philipp Oeser commented

2021-08-03 10:53:43 +02:00

Closed as duplicate of #45493

Philipp Oeser closed this issue

2021-08-03 10:53:43 +02:00

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automatic weights ignores loose parts #90340