Remove blending features from AnimationPlayer

[TokageItLab]

See also

• AnimationPlayer blending and AnimationTree blending are inconsistent #70207
• Remove blending feature Default Blend Time from AnimationPlayer godot-proposals#5952

AnimationPlayer has a blending feature, but it is difficult to make it consistent with AnimationTree's new blending algorithm. Also, there is a lot of code duplication between AnimationPlayer and AnimationTree, which reduces maintainability and stability.

By removing them, AnimationPlayer will have a simple and straightforward implementation, and advanced use cases such as blending can be handled by AnimationTree and AnimationStateMachine, which make us to be able to separate use cases clearly. And we should focus on stabilizing behevior and improving the usability of StateMachine.

I guess the code could be simplified further than this PR, but for now I will keep the changes to a minimum. We will be able to refactor it later if necessary.

If this feature is removed, it should not be a problem because there are already features that cover it as AnimationTree and AnimationStateMachine. And that is what should generally be used.

By the way, Capture Mode is not a problem here, so it will remain. No worries.

Closes #70207
Closes godotengine/godot-proposals#5952

[fire]

I support removing the duplicated blending code. There are two sets of blending and the animation tree is the main one. So it makes sense to remove the animation player duplicate.

[reduz]

There is no chance on this happening, way too many users use this workflow. Once something major is there, you cause a lot of pain to users if you want to remove it. Either some code deduplication is done to reuse it between nodes or this has to be left as is.

[TokageItLab]

I assume that some few users are using this, but obviously it is a territory invasion to have this feature in AnimationPlayer.

The Transform3D tracks do not blend well and the AudioTrack blending is inconsistent with AnimationTree. I tried to make the blending consistent between AnimationPlayer and AnimationTree with the duplication, but the accumulator was not working properly (perhaps this is because the blend weights exceed 1.0 and current AnimationPlayer blending rely on the same behavior as the old broken AddBlend #37661) so I gave up. Also, it requires many hacks in many places to avoid blending with ownself or with void, so I am not very inclined to keep this up.

If you are thinking of compatibility with Godot3, it is completely missing the point. Godot3 and Godot4 animations have already lost a lot of compatibility, so it is very difficult to port Godot3 animations into Godot4 even if there is a converter.

It may be possible to keep this feature as is, but no one can maintain it and it is a deprecated feature in my opinion.

[fire]

@reduz if you wish, it can be marked deprecated for godot 4, but I am not sure we are able to restore the animation player blending workflow to 100% working. @TokageItLab's opinion is written in this discussion.

[smix8]

I personally use the AnimationPlayer blending all the time in plenty of projects for simple stuff that does not justify using a complex AnimationTree or would add so much unnecessary complexity that comes with working with scripts and AnimationTree that it becomes a nuisance. I am fine with using an AnimationTree for more complex stuff but I would prefer if at least simple blending would stay as an option in AnimationPlayer.

[TokageItLab]

Will be superseded by godotengine/godot-proposals#5972