When the `Unity Timeline` window exists, entering play mode will clear animation curves when using `AnimationClip.SetCurve` in conjunction with `AnimationUtility.SetObjectReferenceCurve`

ColorlessColor commented 2 months ago

Test Environment

Unity version: 2022.3.22f1
VRChat SDK version: 3.6.1
Modular Avatar version: 1.9.13
NDMF version: 1.4.1
lilToon version: 1.7.3

Issue Description

Reproduction Steps

Create a VRChat Avatar project and install Modular Avatar.
Open a scene, put in a avatar and a clothes prefab which is using MA Merge Armature. Assuming the Unity scene is as follows, with all GameObjects activated:
```
AvatarRoot
Armature
ClothesUseMA
Armature            // `MA Merge Armature` on this
  Hips
    skirtPbRoot     // phys bone of skirt
SkirtMesh
```
Record an animation clip that includes:
- Deactivating AvatarRoot/ClothesUseMA/Armature/Hips/skirtPbRoot (this is a float curve^1).
- Changing the material of AvatarRoot/ClothesUseMA/SkirtMesh (this is an object reference curve^2).
Place this animation clip in any playable layer (e.g., FX).
Open Unity Timeline window.
Click the Play button.
Check the animation clip that has been rewritten by MA Merge Armature.

Expected Behavior

The animation property with the path AvatarRoot/ClothesUseMA/Armature/Hips/skirtPbRoot should be rewritten and exist in the new animation clip.
The material switching animation property with the path AvatarRoot/ClothesUseMA/SkirtMesh should exist and its path should not be rewritten.

Actual Behavior

The property with the path AvatarRoot/ClothesUseMA/Armature/Hips/skirtPbRoot is missing!
The material switching animation property with the path AvatarRoot/ClothesUseMA/SkirtMesh should exist and its path should not be rewritten.

Possible Cause

https://github.com/bdunderscore/modular-avatar/blob/0806c621c5298fa2ec89d2590e8015f6a84fcf3a/Editor/Animation/PathMappings.cs#L248-L262

PathMappings.ApplyMappingsToClip is used to rewrite animation clips' paths associated with GameObjects modified by MA Merge Armature.

The issue arises when SetCurve is first used to write float curves, followed immediately call a AnimationUtility.SetObjectReferenceCurve. In the provided reproduction environment and steps, this results in all animation curves in newClip being cleared (I really don't know why).

The animation curve lost occurs only when the following conditions are met simultaneously:

The Unity Timeline window is exist.
Entering Play mode.
Calling SetCurve on the animation clip immediately followed by AnimationUtility.SetObjectReferenceCurve, without any other method calls on the animation clip in between.

The issue can be bypassed by the following methods:

Close the Unity Timeline window.
Use AnimationUtility.SetEditorCurve instead of SetCurve.
Calling AnimationUtility.GetCurveBindings (or possibly other functions) on the animation clip between SetCurve and AnimationUtility.SetObjectReferenceCurve (note: even simply accessing or observing the animation clip's value in the debugger may cause the bug to disappear).

Notes

This issue does not affect Manual bake avatar or uploading using the VRChat Avatar SDK.

The issue has only been verified on Unity 2022.3.22f1 and has not been tested on any other versions. Only tested on my Unity installation (I tried reinstall it).

I suspect this is an issue with Unity's animation system itself, and perhaps Modular Avatar does not need to address this specifically, but rather users should avoid using Unity Timeline.

I chose to report this issue because I spent too much time on it and hope that this report will help users who encounter similar issues.

bdunderscore commented 2 months ago

Thanks, I hate it. 🤮

I'll try to repro and fix.

bdunderscore commented 2 months ago

Hmm. I wasn't able to repro the issue with the steps given. That being said, I'll assume there's something else that's a necessary condition and switch to using SetEditorCurve as workaround.

ColorlessColor commented 2 months ago

I created a project for this if anyone needs it:

https://github.com/ColorlessColor/CursedUnityTimeline

bdunderscore commented 2 months ago

Reproed and changing to SetEditorCurve doesn't fix the issue :(

bdunderscore commented 2 months ago

Only reproducible when entering play mode; building manually doesn't cause the issue. I think reload domain might need to be off as well...

bdunderscore / modular-avatar