Separate Sub(Nested)StateMachine and StateMachineGroup processes

[TokageItLab]

Describe the project you are working on

3D character game

Describe the problem or limitation you are having in your project

StateMachines can be grouped. But SubStateMachine i.e. a nested StateMachine has a state separate from its parent StateMachine.

For example, if we have StateMachine A and StateMachine B, B exists as a state "sub" within A. While StateMachine A is in state "sub", StateMachine B runs, but the state of StateMachine A can be changed without regard to the state of StateMachine B.

This leaves StateMachine B in a stuck state, which causes problems when resuming as godotengine/godot#68986 and godotengine/godot#62576.

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

For StateMachineGroup, disallow abort until End State. Or, as mentioned in godotengine/godot#62576, disallow a StateMachineGroup to have a separate State. It ensures that there are no stuck states.

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

I am considering whether to flag StateMachineGroup as a bool value in the parent StateMachine or make it a separate class.

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

No.

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

AnimationStateMachine is core.

[TokageItLab]

I was thinking a little about the details of the implementation, so I'll leave a note for myself.

Implement the bool grouping property. Default is true.

If the grouping property is true, internal seek to 0 means transition to the Start state.

If the parent of a grouping StateMachine is also a grouping StateMachine, it is prohibited from seeking the playback of the child grouping StateMachine.

Instead, make the parent grouping StateMachine's playback available to the child grouping StateMachine's path.

[TokageItLab]

Closed by godotengine/godot#75759