问帧影的动画不透明度

EN

<script src="https://aframe.io/releases/1.3.0/aframe.min.js"></script>
<script src="https://gftruj.github.io/webzamples/aframe/models/components/model-opacity.js"></script>
<script>
  AFRAME.registerComponent("relative-shadow", {
    schema: {
      target: { type: "selector" }
    },
    init: function() {
      const mesh = this.el.getObject3D("mesh"); // grab the mesh
      const oldMaterial = mesh.material; // store the old material
      mesh.material = this.material = new THREE.ShadowMaterial(); // apply a shadow material
      oldMaterial.dispose(); // dispose the old material
    },
    update: function() {
      this.opacitySource = this.data.target.components["model-opacity"]; // react to the target being set
    },
    tick: function() {
      if (!this.opacitySource) return; // wait until we can access the opacity value
      // update the opacity using the t-rex material opacity from the component
      this.material.opacity = this.opacitySource.data.opacity;
    }
  })
</script>
<a-scene>
  <a-asset-item id="spino" src="https://rawcdn.githack.com/krlosflip22/aframe-ar-sample/c91a7a9dd8b1428bc8e68bc1b5d8641d7241fd1b/spinosaurus.glb"></a-asset-item>
  <a-gltf-model id="trex" position="0 1 -4" shadow="cast: true" scale="0.5 0.5 0.5" src="#spino" model-opacity 
                animation="property: model-opacity.opacity; to: 0; dur: 1000; dir: alternate; loop: true;"></a-gltf-model>
  
  <a-plane rotation="-90 0 0" scale="40 40 40" 
           relative-shadow="target: #trex" shadow="receive: true"></a-plane>
  <a-sky color="#ECECEC"></a-sky>
</a-scene>

<iframe width="100%" height="100%" src="https://r105.threejsfundamentals.org/threejs/threejs-shadows-fake.html"></iframe>