spark/examples/animation-skinning/index.html

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <title>Forge • Animation • Skinning</title>
  <style> body {margin: 0;} </style>
</head>
<body>
  <script type="importmap">
    {
      "imports": {
        "three": "/examples/js/vendor/three/build/three.module.js",
        "@forge-gfx/forge": "/dist/forge.module.js"
      }
    }
  </script>
  <script type="module">
    import * as THREE from "three";
    import { SplatMesh, SplatSkinning } from "@forge-gfx/forge";
    import { getAssetFileURL } from "/examples/js/get-asset-url.js";

    const scene = new THREE.Scene();
    const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
    const renderer = new THREE.WebGLRenderer();
    renderer.setSize(window.innerWidth, window.innerHeight);
    document.body.appendChild(renderer.domElement)

    function gridToBoneIndex(x, y) {
      return 15 * (y + 7) + (x + 7);
    }

    const splatURL = await getAssetFileURL("butterfly.spz");
    const butterfly = new SplatMesh({
      url: splatURL,
      onLoad: (mesh) => {
        // Make a 15x15 uniform grid of bones on the XY plane
        const skinning = new SplatSkinning({ mesh, numBones: 15 * 15 });
        const position = new THREE.Vector3();
        const quaternion = new THREE.Quaternion();
        for (let y = -7; y <= 7; y++) {
          for (let x = -7; x <= 7; x++) {
            position.set(x * 0.05, y * 0.05, 0);
            skinning.setRestQuatPos(gridToBoneIndex(x, y), quaternion, position);
          }
        }

        // Compute bone indices and weights for each Gsplat such that
        // it uses the 4 nearest bones in a bilinear manner.
        const boneIndices = new THREE.Vector4();
        const weights = new THREE.Vector4();
        mesh.forEachSplat((index, center) => {
          const x = center.y / 0.05;
          const y = center.x / 0.05;
          const gridX = Math.max(-7, Math.min(6, Math.floor(x)));
          const gridY = Math.max(-7, Math.min(6, Math.floor(y)));
          const fractX = Math.max(0, Math.min(1, x - gridX));
          const fractY = Math.max(0, Math.min(1, y - gridY));
          boneIndices.set(
            gridToBoneIndex(gridX, gridY),
            gridToBoneIndex(gridX + 1, gridY),
            gridToBoneIndex(gridX, gridY + 1),
            gridToBoneIndex(gridX + 1, gridY + 1),
          );
          weights.set(
            (1 - fractX) * (1 - fractY),
            fractX * (1 - fractY),
            (1 - fractX) * fractY,
            fractX * fractY,
          );
          skinning.setSplatBones(index, boneIndices, weights);
        });

        mesh.skinning = skinning;
        mesh.updateGenerator();
      },
    });
    butterfly.quaternion.set(1, 0, 0, 0);
    butterfly.position.set(0, 0, -1);
    scene.add(butterfly);

    renderer.setAnimationLoop(function animate(time) {
      renderer.render(scene, camera);
      if (butterfly.skinning) {
        // Making sure async loading and initialization is complete
        const position = new THREE.Vector3();
        const quaternion = new THREE.Quaternion();
        for (let y = -7; y <= 7; y++) {
          for (let x = -7; x <= 7; x++) {
            position.set(x * 0.05, y * 0.05, 0);
            // Rotate Gsplats to flap the wings
            quaternion.setFromEuler(
              new THREE.Euler(
                x * 0.09 * Math.sin(time * 0.0011),
                y * 0.05 * Math.cos(time * 0.0071),
                0.2 * Math.sin(time * 0.0011),
              ),
            );
            butterfly.skinning.setBoneQuatPos(gridToBoneIndex(x, y), quaternion, position);
          }
        }
        butterfly.skinning.updateBones();
      }
    });
  </script>
</body>
</html>