Expose low-level properties of AnimationTree

[Daylily-Zeleen]

Describe the project you are working on

An rollbackable 3D Game.

Describe the problem or limitation you are having in your project

Hitting detection boxs of character are bind with skeleton, and we can't save AnimationTree's properties as state and load the state to support rollback.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

We can realize the rollback of animation by providing apis to get and set private properties of AnimationTree.

Because of hitting detection often work with skeleton in 3D game, this feature is beneficial to do prediction with physics simulation.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Provide a series of get and set methods of private properties, and register them as property in ClassDB (maybe add a prefix "advance_" for each property is better).

If this enhancement will not be used often, can it be worked around with a few lines of script?

We can't manipulate private properties of AnimationTree in script.

Is there a reason why this should be core and not an add-on in the asset library?

We can't implement a rollbackable AnimationTree by inheriting.

[Calinou]

• Related to Add ability to simulate physics manually/multiple times at once #2821.

[fire]

To implement rollback features, create a secure API that manages rollbacks without compromising the internal AnimationTree properties.

Extend the AnimationTree class with an AnimationTreeRecorder class, including "buffer time" and "rollback time" properties for recording and rolling back states.

Exposing AnimationTree properties is not accepted, but integrating an AnimationTreeRecorder class into the core may be more favourable.

See godotengine/godot#77347 (comment) for the original comment.