animation-tree

AnimationTree — Wire Clips Into Behavior

Generation gives you clips. The AnimationTree gives the character life. This skill is not generative — no FAL, no MCP AI calls. It composes existing clips on an AnimationPlayer into an AnimationTree with a StateMachine for distinct states (idle / attack / hit / dead) and BlendSpace nodes for continuous parameters (walk-run blend by speed). Done right, the character moves like a shipped game; done wrong, you get T-poses, snapping, or animations that "eat" each other.

The canonical Summer Engine stack:

Character (CharacterBody3D)
├── Skeleton3D (from the Meshy rig)
├── AnimationPlayer            # holds the raw clips (idle, walk, run, attack_sword, ...)
└── AnimationTree              # references AnimationPlayer, drives behavior

Before adding the tree, prove direct AnimationPlayer.play() visibly moves the rig. Godot may import animation GLBs as AnimationLibrary resources or as PackedScenes with embedded AnimationPlayers. If a copied clip appears in the list but the mesh T-poses, its tracks probably target a different root/skeleton path. Use the embedded player that came with the matching GLB, or remap/copy tracks only after confirming they target the active Skeleton3D. An inactive AnimationTree is also a no-op, so always set AnimationTree.active = true.

When to use this skill

• Character has 3+ clips and switching between them via AnimationPlayer.play("walk") is causing pops, T-poses, or "starts halfway through".
• Need a walk → run blend that's continuous, not boolean.
• Need attack to interrupt locomotion but only on the upper body, while feet keep walking.
• Need hit-react one-shot that returns to whatever state was playing before.
• Building any non-trivial NPC or player character past the prototype phase.

When NOT to use this skill

• Single-clip looping background prop (banner waving, water surface). Just AnimationPlayer.play("loop") is fine.
• Cinematic with hand-authored timing. Use AnimationPlayer directly with play_with_capture; AnimationTree is overkill.
• Character has zero clips — generate first via summer:animation/generate-motion.
• Procedural-only animation (no clips, all IK). That's summer:animation/procedural-animation.