Vertex groups of fake user mesh data go missing when loading old files in 3.0 #94128

New Issue

Takuya Sawatari · 2021-12-15T21:51:41+01:00

Takuya Sawatari commented

2021-12-15 21:51:41 +01:00

System Information
Operating system: Linux-5.8.0-63-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.91.03

Blender Version
Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: f1cca30557
Worked: 2.93.4

Short description of error
When loading a .blend file saved in 2.93 in 3.0, vertex groups of unused (only fake user) mesh data get lost.

After searching around I'm assuming it's because of this: https://developer.blender.org/rB3b6ee8cee7080af200e25e944fe30d310240e138

Exact steps for others to reproduce the error

Create a mesh in version 2.93.4.
Add some vertex groups to it.
Set the fake user toggle for the mesh data.
Duplicate the mesh object.
Delete the original mesh object. (Its mesh data now only has a fake user)
Save the .blend file.
Load the .blend file in version 3.0
Notice that the vertex groups in the duplicate mesh object are still there.
Switch the duplicate mesh object to use the original (fake user) mesh data.
Notice that the vertex group list is empty.

**System Information** Operating system: Linux-5.8.0-63-generic-x86_64-with-glibc2.31 64 Bits Graphics card: GeForce GTX 1060 6GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.91.03 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `f1cca30557` Worked: 2.93.4 **Short description of error** When loading a .blend file saved in 2.93 in 3.0, vertex groups of unused (only fake user) mesh data get lost. After searching around I'm assuming it's because of this: https://developer.blender.org/rB3b6ee8cee7080af200e25e944fe30d310240e138 **Exact steps for others to reproduce the error** 1. Create a mesh in version 2.93.4. 2. Add some vertex groups to it. 3. Set the fake user toggle for the mesh data. 4. Duplicate the mesh object. 5. Delete the original mesh object. (Its mesh data now only has a fake user) 6. Save the .blend file. 7. Load the .blend file in version 3.0 8. Notice that the vertex groups in the duplicate mesh object are still there. 9. Switch the duplicate mesh object to use the original (fake user) mesh data. 10. Notice that the vertex group list is empty.

Takuya Sawatari commented

2021-12-15 21:51:41 +01:00

Added subscriber: @Takuya

Hans Goudey commented

2021-12-16 00:00:08 +01:00

Added subscriber: @HooglyBoogly

Hans Goudey commented

2021-12-16 00:00:08 +01:00

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

Hans Goudey closed this issue

2021-12-16 00:00:08 +01:00

Hans Goudey commented

2021-12-16 00:00:08 +01:00

Thanks for the report. This is expected behavior though. Because the vertex group names used to be stored on the object, they were removed after you deleted it in 2.93.
In 2.93, this worked because the duplicate object also happened to have a vertex group (because it came from the first object).
If you delete the vertex group on the duplicate object before switching it back to the first mesh, you'll notice it didn't work anymore.

In other words, before, the mesh couldn't functionally have any vertex groups without being attached to an object. Now, in 3.0 it can, since the vertex group names are also stored there.

I hope that makes sense, does it?

Thanks for the report. This is expected behavior though. Because the vertex group names used to be stored on the object, they were removed after you deleted it in 2.93. In 2.93, this worked because the duplicate object also happened to have a vertex group (because it came from the first object). If you delete the vertex group on the duplicate object before switching it back to the first mesh, you'll notice it didn't work anymore. In other words, before, the mesh couldn't functionally have any vertex groups without being attached to an object. Now, in 3.0 it can, since the vertex group names are also stored there. I hope that makes sense, does it?

Takuya Sawatari commented

2021-12-16 08:41:54 +01:00

Thanks for explaining. 3b6ee8cee7 actually did the opposite of what my tired brain understood last night. So my missing vertex group names were never stored in the mesh data in the first place. Now it makes sense.
I was testing a character's weights in different poses, and was switching back and forth between 2 versions of the mesh data with different weights, but with the same vertex group names, so I never noticed.

Thanks for explaining. 3b6ee8cee708 actually did the opposite of what my tired brain understood last night. So my missing vertex group names were never stored in the mesh data in the first place. Now it makes sense. I was testing a character's weights in different poses, and was switching back and forth between 2 versions of the mesh data with different weights, but with the same vertex group names, so I never noticed.

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Vertex groups of fake user mesh data go missing when loading old files in 3.0 #94128