AnimationPlayer class final

Plays AnimationClips onto animation targets.

The player writes through setPosition / setRotation / setScale, which is all it has to do: the version counters on a scene node make everything derived from a transform — world matrices, bounds, normal matrices — refresh on their own. There is no invalidation to remember and no update pass to run in the right order.

One clip at a time, crossfading between two: crossFadeTo keeps the clip being left over playing while the new one comes in, because cutting straight to the new pose is what makes a character look as though it teleports between animations.

And layers over the top of that, each one a clip on the joints its mask names — an upper body that reloads while the legs keep running. A crossfade moves the whole skeleton; a layer moves part of it and leaves the rest alone. See AnimationLayer, which says why it overrides rather than adds, and AnimationMask, which says why a mask is indices.

The base is applied first and a layer writes over it, so a player with no layers poses exactly as it did before there were any — animation_layer_test holds that, because a feature that moved every existing character by a hair would have been a feature that moved every golden.

Additive blending is still a separate feature. What is missing above this is a state machine that decides which clip — that belongs to the game layer, not here.