AnimationMixer

• clipAction(clip) returns a reusable AnimationAction; call play(), setLoop(), and fadeIn() on it to control playback.
• Pass delta time in seconds to update(); setTime() jumps to a specific point for scrubbing.
• Listen for the 'finished' event on the mixer to detect when non-looping actions end.

const loader = new GLTFLoader();

loader.load('/models/escalator.glb', function (gltf) {
  scene.add(gltf.scene);

  const mixer = new THREE.AnimationMixer(gltf.scene);

  gltf.animations.forEach(function (clip) {
    const action = mixer.clipAction(clip);
    action.setLoop(THREE.LoopRepeat, Infinity);
    action.play();
  });

  mixer.addEventListener('finished', function (event) {
    console.log('播放结束', event.action.getClip().name);
  });

  clock.start();

  renderer.setAnimationLoop(function () {
    const delta = clock.getDelta();
    mixer.update(delta);
    renderer.render(scene, camera);
  });
});

const idle = mixer.clipAction(idleClip);
const walk = mixer.clipAction(walkClip);

idle.play();
walk.play();
walk.setEffectiveWeight(0);       // 先挂上，权重为 0
function blendToWalk(t) {
  walk.setEffectiveWeight(t);
  idle.setEffectiveWeight(1 - t);
}

• stopAllAction() freezes the model on its last pose; reset action time to 0 and call update(0) to restore the bind pose.
• Mixers are per root object, so animated models loaded separately need separate AnimationMixer instances.