Data Transfer modifier & Transfer Weights operator don't work with the source on "All Layers" if the source mesh has vertex groups that the target mesh doesn't. #61255

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Demeter Dzadik · 2019-02-06T20:39:25+01:00

Demeter Dzadik commented

2019-02-06 20:39:25 +01:00

Blender Version
Broken: Since 2.7, also broken in 2.8.
Worked: Probably never?

Short description of error
I'm trying to transfer vertex groups from all layers of a source mesh to all layers of a target mesh, matching by the vertex group name, ie default settings. This only seems to work if the target mesh has every single vertex group that the source mesh does. This seems like an unnecessary requirement for the modifier to work - It should transfer the vertex groups that exist in both meshes, and either ignore or create the ones that don't, depending on Create Data option.

In the example below I'm using the Data Transfer modifier, but the Transfer Weights operator seems to behave the same way when source is set to "All Layers". All other source settings seem to be working fine.

Exact steps for others to reproduce the error
datatransfer_bug.blend

Download attached blend (It's a 2.7 blend file so it should work in both that and 2.8)
Note that the weights in "Group1" are being transfered "from"->"to" successfully.
Delete "Group2" in "to"
"Group1" is no longer being transferred.

I'm aware there is a button in the modifier that creates all the vertex groups in the target mesh that it needs, but I think the modifier should be working without having to press that button.

**Blender Version** Broken: Since 2.7, also broken in 2.8. Worked: Probably never? **Short description of error** I'm trying to transfer vertex groups from all layers of a source mesh to all layers of a target mesh, matching by the vertex group name, ie default settings. This only seems to work if the target mesh has every single vertex group that the source mesh does. This seems like an unnecessary requirement for the modifier to work - It should transfer the vertex groups that exist in both meshes, and either ignore or create the ones that don't, depending on Create Data option. In the example below I'm using the Data Transfer modifier, but the Transfer Weights operator seems to behave the same way when source is set to "All Layers". All other source settings seem to be working fine. **Exact steps for others to reproduce the error** [datatransfer_bug.blend](https://archive.blender.org/developer/F6530880/datatransfer_bug.blend) - Download attached blend (It's a 2.7 blend file so it should work in both that and 2.8) - Note that the weights in "Group1" are being transfered "from"->"to" successfully. - Delete "Group2" in "to" - "Group1" is no longer being transferred. I'm aware there is a button in the modifier that creates all the vertex groups in the target mesh that it needs, but I think the modifier should be working without having to press that button.

Demeter Dzadik commented

2019-02-06 20:39:25 +01:00

Added subscriber: @Mets

Bastien Montagne was assigned by Campbell Barton

2019-02-07 00:12:17 +01:00

Demeter Dzadik changed title from ~~Data Transfer modifier doesn't work at all if the source mesh has ANY vertex groups that the target mesh doesn't.~~ to Data Transfer modifier & Transfer Weights operator don't work with the source on "All Layers" if the source mesh has vertex groups that the target mesh doesn't.

2019-02-07 00:57:34 +01:00

Bastien Montagne commented

2019-02-07 08:47:59 +01:00

Changed status from 'Open' to: 'Archived'

Bastien Montagne closed this issue

2019-02-07 08:47:59 +01:00

Bastien Montagne commented

2019-02-07 08:47:59 +01:00

No, modifier should absolutely not create missing vgroups, never ever. Because vgroups are actually defined in the object, not the mesh (while weights are being stored in mesh's custom data). Yes, this design is (very) bad, and has been biting us for ages, adding lots of limitations and weird/buggy behaviors (try to assign the same mesh to two objects with different vgroups…).

But modifiers shall absolutely not modify object itself, since that would be no more 'on the fly' changes. So thanks for the report, but having to use the Generate Data Layers button is considered a known limitation of current data design, definitively not a bug.

No, modifier should absolutely not create missing vgroups, never ever. Because vgroups are actually defined in the object, not the mesh (while weights are being stored in mesh's custom data). Yes, this design is (very) bad, and has been biting us for ages, adding lots of limitations and weird/buggy behaviors (try to assign the same mesh to two objects with different vgroups…). But modifiers shall absolutely not modify object itself, since that would be no more 'on the fly' changes. So thanks for the report, but having to use the Generate Data Layers button is considered a known limitation of current data design, definitively not a bug.

Demeter Dzadik commented

2019-02-07 12:38:11 +01:00

Thanks Mont, I understand, that explains why the modifier isn't allowed to create vertex groups, but! I still think that it should transfer the weights from vertex groups that exist on the source mesh into matching vertex groups that exist in the target mesh. This doesn't involve creating any new vertex groups, it just means the modifier would ignore any vertex groups that exist in the source mesh and don't exist in the target mesh. I think this behaviour would be fairly intuitive from a user perspective, and doesn't require the modifier to mess with data that is owned by the object.

Also, the Transfer Weights operator is not a modifier, so shouldn't that be allowed to change object data and add vertex groups? It already does this when the source setting is set to "Selected Pose bones" or "Deform Pose Bones". It only doesn't work with "All Layers".

Thanks Mont, I understand, that explains why the modifier isn't allowed to create vertex groups, but! I still think that it should transfer the weights from vertex groups that exist on the source mesh into matching vertex groups that exist in the target mesh. This doesn't involve creating any new vertex groups, it just means the modifier would ignore any vertex groups that exist in the source mesh and don't exist in the target mesh. I think this behaviour would be fairly intuitive from a user perspective, and doesn't require the modifier to mess with data that is owned by the object. Also, the Transfer Weights operator is not a modifier, so shouldn't that be allowed to change object data and add vertex groups? It already does this when the source setting is set to "Selected Pose bones" or "Deform Pose Bones". It only doesn't work with "All Layers".

Bastien Montagne commented

2019-02-07 15:44:59 +01:00

Afaik transfer data operator works as expected (i.e. generates needed layers). Note that it works from active object (source) to all other selected objects (destinations).
Transfer Weights is same operator as data transfer, but works reversed (from selected object to active, that was done that way to mimic old weight transfer operator that existed before generic data transfer one was added).

Regarding vgroups being shared between objects and meshes data-blocks, imho this should be changed at some point yes (probably only be defined into meshes, and lattices, like any other geometry data). But that kind of change is not that easy to be made, so there is no firm plans about it currently.

Afaik transfer data operator works as expected (i.e. generates needed layers). Note that it works from active object (source) to all other selected objects (destinations). Transfer Weights is same operator as data transfer, but works reversed (from selected object to active, that was done that way to mimic old weight transfer operator that existed before generic data transfer one was added). Regarding vgroups being shared between objects and meshes data-blocks, imho this should be changed at some point yes (probably only be defined into meshes, and lattices, like any other geometry data). But that kind of change is not that easy to be made, so there is no firm plans about it currently.

Demeter Dzadik commented

2019-02-07 16:38:25 +01:00

You're right in that the Data Transfer operator works as intended in the cases where "Create Data" is enabled.

However, if "Create Data" is disabled, and "Source Layers" is set to "All Layers" it will not do ANYTHING unless the destination mesh has every vertex group that the source mesh does.

transfer_weights_operator.webm

As you can see, both the source and the destination mesh has a "Group1" vgroup, and yet, it doesn't get transferred. The fact that "Group2" does not get transferred makes perfect sense since "Create Data" is turned off, but the fact that "Group1" does not get transferred just because "Group2" exists in the source mesh is really odd.

And the same thing goes for the modifier:
transfer_weights_modifier.webm

I see no reason why the weights in "Group1" shouldn't be transferred just because "Group2" doesn't exist. I'm assuming the code checks if ALL of the source vertex groups can be found in the destination object, and if not, it will do absolutely nothing. Instead, it should make a list of the vertex groups that DO exist in the destination object, and transfer the weights from just those groups, ignoring the rest.

So I still definitely think that there is a bug to be fixed here! Probably two for the price of one, even! :)

You're right in that the Data Transfer operator works as intended in the cases where "Create Data" is enabled. However, if "Create Data" is disabled, and "Source Layers" is set to "All Layers" it will not do ANYTHING unless the destination mesh has every vertex group that the source mesh does. [transfer_weights_operator.webm](https://archive.blender.org/developer/F6539766/transfer_weights_operator.webm) As you can see, both the source and the destination mesh has a "Group1" vgroup, and yet, it doesn't get transferred. The fact that "Group2" does not get transferred makes perfect sense since "Create Data" is turned off, but the fact that "Group1" does not get transferred just because "Group2" exists in the source mesh is really odd. And the same thing goes for the modifier: [transfer_weights_modifier.webm](https://archive.blender.org/developer/F6539810/transfer_weights_modifier.webm) I see no reason why the weights in "Group1" shouldn't be transferred just because "Group2" doesn't exist. I'm assuming the code checks if ALL of the source vertex groups can be found in the destination object, and if not, it will do absolutely nothing. Instead, it should make a list of the vertex groups that DO exist in the destination object, and transfer the weights from just those groups, ignoring the rest. So I still definitely think that there is a bug to be fixed here! Probably two for the price of one, even! :)

Bastien Montagne commented

2019-02-08 09:26:30 +01:00

Well, that’s not really a bug, as in, code was written to behave that way (abort/do nothing in case some destination vgroups are missing). But I agree it would be better in fact to transfer what we can, will change that (will indeed affect both operator and modifier, since they share 99% of the code ;) ).

blender-admin commented

2019-02-08 10:12:31 +01:00

This issue was referenced by 0e3475b00d

This issue was referenced by 0e3475b00d44bc0220cee84d28daacaa6735f62f

Bastien Montagne commented

2019-02-08 10:16:23 +01:00

Changed status from 'Archived' to: 'Resolved'

Demeter Dzadik commented

2019-02-08 15:15:12 +01:00

I love you!

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Data Transfer modifier & Transfer Weights operator don't work with the source on "All Layers" if the source mesh has vertex groups that the target mesh doesn't. #61255