I have written an animation player, about 5000 lines of code. It has been tested and runs well, serialization and designer have also been completed.
However, there is an issue:
Animations need to call Update every frame, and TAnimationPlayer is inherited from TCastleComponent. I had to register two additional controls: TCastleAnimationPlayer = class(TCastleUserInterface) and TCastleAnimationPlayerTransform = class(TCastleTransform), both of which have TAnimationPlayer as a subcomponent.

I wonder if TAnimationPlayer can be registered directly as a TCastleBehavior without the need for two additional controls. However, TCastleUserInterface cannot use TCastleBehavior. Can it be added?