Store/Remove Named Attribute issues with vertex groups #99873

New Issue

Alexander Gavrilov · 2022-07-20T14:16:34+02:00

Alexander Gavrilov commented

2022-07-20 14:16:34 +02:00

Blender Version

Broken: 3.3 alpha 8d69c6c4e7

Short description of error

Using geometry nodes to store or remove vertex groups doesn't work correctly.

Exact steps for others to reproduce the error

Open the file:

test-store-attribute.blend

It contains examples of Store and Remove Named Attribute, paired with an emulation using the Vertex Weight Mix modifier: the bottom 4 lines should form two identical pairs. However, the geometry node versions instead look like the top line, which is incorrect.

Technical analysis

The problem in the Store Named Attribute is that it starts by deleting the attribute, i.e. basically does Remove Named Attribute first. This loses the attribute's identity as a vertex group, and also triggers the Remove issue.

Remove Named Attribute appears to trigger a bug in the Armature modifier where it for some reason uses the original list of vertex groups with evaluated weight data, thus causing a shift mismatch with the names (emulated by the top line).

**Blender Version** Broken: 3.3 alpha 8d69c6c4e7 **Short description of error** Using geometry nodes to store or remove vertex groups doesn't work correctly. **Exact steps for others to reproduce the error** Open the file: [test-store-attribute.blend](https://archive.blender.org/developer/F13303020/test-store-attribute.blend) It contains examples of Store and Remove Named Attribute, paired with an emulation using the Vertex Weight Mix modifier: the bottom 4 lines should form two identical pairs. However, the geometry node versions instead look like the top line, which is incorrect. **Technical analysis** The problem in the Store Named Attribute is that it starts by deleting the attribute, i.e. basically does Remove Named Attribute first. This loses the attribute's identity as a vertex group, and also triggers the Remove issue. Remove Named Attribute appears to trigger a bug in the Armature modifier where it for some reason uses the original list of vertex groups with evaluated weight data, thus causing a shift mismatch with the names (emulated by the top line).

Alexander Gavrilov commented

2022-07-20 14:16:34 +02:00

Added subscriber: @angavrilov

Alexander Gavrilov commented

2022-07-20 14:17:28 +02:00

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

Alexander Gavrilov commented

2022-07-20 14:17:28 +02:00

Added subscriber: @HooglyBoogly

Hans Goudey self-assigned this 2022-07-22 00:50:56 +02:00

Alexander Gavrilov commented

2022-07-22 13:38:25 +02:00

There is one more issue with deleting groups that I noticed by the way: the viewport weight overlay also seems to use original name mapping when displaying weights for the active vertex group/bone and is affected by the same shift mismatch. But maybe that should be a separate bug to simplify tracking...

Hans Goudey commented

2022-07-22 16:29:06 +02:00

That's partially solved by adding this code to VertexGroupsAttributeProvider::try_delete:

    if (index < mesh->vertex_group_active_index) {
      mesh->vertex_group_active_index--;
    }

However, I'm not sure what should happen when you delete the active vertex group. I guess the overlay should just turn off then?

That's partially solved by adding this code to `VertexGroupsAttributeProvider::try_delete`: ``` if (index < mesh->vertex_group_active_index) { mesh->vertex_group_active_index--; } ``` However, I'm not sure what should happen when you delete the active vertex group. I guess the overlay should just turn off then?

blender-admin commented

2022-07-22 17:31:10 +02:00

This issue was referenced by c40971d79a

This issue was referenced by c40971d79a887820d621705b29f65f833d9b9f52

Hans Goudey commented

2022-07-22 17:33:44 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Hans Goudey closed this issue

2022-07-22 17:33:44 +02:00

Alexander Gavrilov commented

2022-07-22 17:58:51 +02:00

In #99873#1394194, @HooglyBoogly wrote:
That's partially solved by adding this code to VertexGroupsAttributeProvider::try_delete:

No, the problem is the same as with the Armature modifier: the overlay rendering clearly uses indices based on the unevaluated name list, so it displays weights from the wrong group. Painting itself is based on the original mesh with substituted evaluated vertex coordinates so it should be fine, but viewport rendering uses evaluated weights and thus should use evaluated names.

> In #99873#1394194, @HooglyBoogly wrote: > That's partially solved by adding this code to `VertexGroupsAttributeProvider::try_delete`: No, the problem is the same as with the Armature modifier: the overlay rendering clearly uses indices based on the unevaluated name list, so it displays weights from the wrong group. Painting itself is based on the original mesh with substituted evaluated vertex coordinates so it should be fine, but viewport rendering uses evaluated weights and thus should use evaluated names.

Hans Goudey commented

2022-07-22 18:31:23 +02:00

That's not right actually. Renderers like EEVEE and workbench and the overlay engine get evaluated objects with the Object::data field replaced with the evaluated geometry. So the draw cache uses the object-level functions, but those use the names from the evaluated mesh.

Anyway, I wasn't just making that up, I tested both changes and the one I mentioned is the only thing that had an effect.

That's not right actually. Renderers like EEVEE and workbench and the overlay engine get evaluated objects with the `Object::data` field replaced with the evaluated geometry. So the draw cache uses the object-level functions, but those use the names from the evaluated mesh. Anyway, I wasn't just making that up, I tested both changes and the one I mentioned is the only thing that had an effect.

blender-admin commented

2022-07-22 22:49:53 +02:00

This issue was referenced by 80b2fc59d1

This issue was referenced by 80b2fc59d11d5814afe7e219c535525a8d494c17

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Store/Remove Named Attribute issues with vertex groups #99873