NLA data can be added to an overridden object that already has (very hidden, unobvious) animation data #120548

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Albert-OShea · 2024-04-12T04:01:29+02:00

Albert-OShea commented

2024-04-12 04:01:29 +02:00

System Information
Operating system: Windows-10-10.0.22631-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 551.23

Blender Version
Broken: version: 4.1.0, branch: blender-v4.1-release, commit date: 2024-03-25 20:42, hash: 40a5e739e270

Short description of error
Adding NLA strips to overridden objects that already have animation data causes problems, and is already documented in a few issues here, e.g. #109483
My specific problem is how easy it is to mistakenly assume the library object has no animation data attached to it, therefore assuming the linked version of the object is safe to animate on and use NLA on.
There should be some more obvious UI or warning or indicator that the object has animation data in the library file, at least until the NLA is either replaced by the new animation system, or is fully integrated with library linking.
Additionally, clearing the empty animation data of the library object will remove all NLA data in the overridden object. This can potentially be a project-breaking data loss issue.

Exact steps for others to reproduce the error

Download both attached blend files, open main.blend
The 'instancer' object (a linked object) has some NLA data defined in this file. However, because the source library object has animation data, the strips are not working as expected, you cannot delete any of them.
Open library.blend. The object from this file appears to have no animation data. There is no indication of animation data in the outliner.
In the NLA editor, the toggle 'Include Missing NLA' is turned off, which would be very justifiable in a file with a lot of drivers that clutter up the NLA.
Turning on this toggle reveals that the object does in fact have animation data, though with no action linked. This is the only method of determining if the object has animation data without digging through the Data API.
Right click in the NLA track list and select 'Remove Empty Animation Data'. The animation data is now cleared.
Save the file, and open back up main.blend. All the NLA data that was defined in this file is now gone.

**System Information** Operating system: Windows-10-10.0.22631-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 551.23 **Blender Version** Broken: version: 4.1.0, branch: blender-v4.1-release, commit date: 2024-03-25 20:42, hash: `40a5e739e270` **Short description of error** Adding NLA strips to overridden objects that already have animation data causes problems, and is already documented in a few issues here, e.g. https://projects.blender.org/blender/blender/issues/109483 My specific problem is how easy it is to mistakenly assume the library object has no animation data attached to it, therefore assuming the linked version of the object is safe to animate on and use NLA on. There should be some more obvious UI or warning or indicator that the object has animation data in the library file, at least until the NLA is either replaced by the new animation system, or is fully integrated with library linking. Additionally, clearing the empty animation data of the library object will remove all NLA data in the overridden object. This can potentially be a project-breaking data loss issue. **Exact steps for others to reproduce the error** - Download both attached blend files, open `main.blend` - The 'instancer' object (a linked object) has some NLA data defined in this file. However, because the source library object has animation data, the strips are not working as expected, you cannot delete any of them. - Open `library.blend`. The object from this file appears to have no animation data. There is no indication of animation data in the outliner. - In the NLA editor, the toggle 'Include Missing NLA' is turned off, which would be very justifiable in a file with a lot of drivers that clutter up the NLA. - Turning on this toggle reveals that the object does in fact have animation data, though with no action linked. This is the only method of determining if the object has animation data without digging through the Data API. - Right click in the NLA track list and select 'Remove Empty Animation Data'. The animation data is now cleared. - Save the file, and open back up `main.blend`. All the NLA data that was defined in this file is now gone.

main.blend

1.8 MiB

library.blend

777 KiB

Albert-OShea added the

labels 2024-04-12 04:01:30 +02:00

YimingWu commented

2024-04-12 08:34:37 +02:00

Can confirm. Thanks for those detailed reproduction steps.

@dr.sybren Is "animation channel with no action linked" considered a valid action when linking?

Can confirm. Thanks for those detailed reproduction steps. @dr.sybren Is "animation channel with no action linked" considered a valid action when linking?

YimingWu added

and removed

labels 2024-04-12 08:34:51 +02:00

Sybren A. Stüvel commented

2024-04-22 14:14:00 +02:00

Is "animation channel with no action linked" considered a valid action when linking?

I think you mean "has animation data without an action"? Yeah, that's perfectly valid. You can get that with the default startup file very easily, with bpy.data.objects['Cube'].animation_data_ensure(). Or even just by creating a keyframe and then un-assigning the Action.

This report basically shows the inner working of the library override system:

Cube in library.blend has AnimData
Cube in main.blend gets NLA stuff added via an override. In other words, its existing-from-main AnimData gets some overrides to add tracks & strips. This is stored as a "insert into this AnimData" operation.
Cube in library.blend looses its AnimData.
Cube in main.blend gets loaded, and the overrides system sees that the AnimData that should get things added to it no longer exists.

What is described is basically the same as having an override that adds a bunch of vertices to a mesh, and then the entire mesh is removed from the library. There is no more mesh to add vertices to, and this means the new vertices are gone too. Except that with this (hypothetical) mesh example, things are considerably more visible.

This all to say that, unfortunately, this is how the system is currently designed. I don't think that what you describe is a bug per se, but it is unfortunate and feels rather clumsy. I'll talk with @mont29 to see if we can come up with a nice solution.

> Is "animation channel with no action linked" considered a valid action when linking? I think you mean "has _animation data_ without an action"? Yeah, that's perfectly valid. You can get that with the default startup file very easily, with `bpy.data.objects['Cube'].animation_data_ensure()`. Or even just by creating a keyframe and then un-assigning the Action. This report basically shows the inner working of the library override system: 1. Cube in `library.blend` has `AnimData` 2. Cube in `main.blend` gets NLA stuff added via an override. In other words, its existing-from-`main` `AnimData` gets some overrides to add tracks & strips. This is stored as a "insert into this AnimData" operation. 3. Cube in `library.blend` looses its `AnimData`. 4. Cube in `main.blend` gets loaded, and the overrides system sees that the `AnimData` that should get things added to it no longer exists. What is described is basically the same as having an override that adds a bunch of vertices to a mesh, and then the entire mesh is removed from the library. There is no more mesh to add vertices to, and this means the new vertices are gone too. Except that with this (hypothetical) mesh example, things are considerably more visible. This all to say that, unfortunately, this is how the system is currently designed. I don't think that what you describe is a bug per se, but it is unfortunate and feels rather clumsy. I'll talk with @mont29 to see if we can come up with a nice solution.

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NLA data can be added to an overridden object that already has (very hidden, unobvious) animation data #120548