3D Models Articulations Dev

<!--
  示例：用 modelMatrix 驱动模型关节摆动
  说明：机械臂由底座与摆臂两段 GLB 组成，摆臂绕铰点往复摆动；不加载带 articulations 的外部模型
  核心逻辑：Transforms.eastNorthUpToFixedFrame 定位 → 铰点矩阵 → 逐帧左乘绕轴旋转矩阵
  依赖：CesiumJS 1.121 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
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<meta name="viewport" content="width=device-width, initial-scale=1">
<title>模型关节摆动</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Widgets/widgets.css">
<style>
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  .tip{position:absolute;left:12px;top:12px;z-index:5;
       background:rgba(23,28,35,.9);border:1px solid #2a313b;border-radius:6px;
       padding:8px 12px;font-size:12px;color:#a2a9b6;max-width:300px;line-height:1.6}
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<body>
<div id="c"></div>
<div class="tip">灰色方块是底座，浅色长条是摆臂。摆臂的变换矩阵由「铰点 × 旋转」逐帧合成，等同于给模型的一个关节做动画。</div>
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(function () {
  'use strict';

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  /* 生成一个底面贴地的长方体 GLB */
  function boxGlb(w, h, d, color) {
    var hx = w / 2, hz = d / 2;
    var faces = [
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        nor.push(f[4][0], f[4][1], f[4][2]);
      }
      idx.push(base, base + 1, base + 2, base, base + 2, base + 3);
      base += 4;
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    var p = new Float32Array(pos), n = new Float32Array(nor), ix = new Uint16Array(idx);
    var pb = p.byteLength, nb = n.byteLength, ib = ix.byteLength;
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    bin.set(new Uint8Array(n.buffer), pb);
    bin.set(new Uint8Array(ix.buffer), pb + nb);

    var json = {
      asset: { version: '2.0' },
      scene: 0,
      scenes: [{ nodes: [0] }],
      nodes: [{ mesh: 0 }],
      meshes: [{ primitives: [{ attributes: { POSITION: 0, NORMAL: 1 }, indices: 2, material: 0 }] }],
      materials: [{
        pbrMetallicRoughness: {
          baseColorFactor: [color[0], color[1], color[2], 1],
          metallicFactor: 0, roughnessFactor: 0.85
        },
        doubleSided: true
      }],
      accessors: [
        { bufferView: 0, componentType: 5126, count: 24, type: 'VEC3',
          min: [-hx, 0, -hz], max: [hx, h, hz] },
        { bufferView: 1, componentType: 5126, count: 24, type: 'VEC3' },
        { bufferView: 2, componentType: 5123, count: 36, type: 'SCALAR' }
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      ],
      buffers: [{ byteLength: pb + nb + ib }]
    };
    return new Blob([glbBytes(json, bin)], { type: 'model/gltf-binary' });
  }

  var origin = Cesium.Cartesian3.fromDegrees(116.391, 39.907, 0);
  var enu = Cesium.Transforms.eastNorthUpToFixedFrame(origin);

  var baseUrl = URL.createObjectURL(boxGlb(4, 6, 4, [0.32, 0.37, 0.45]));
  var armUrl = URL.createObjectURL(boxGlb(1.4, 7, 1.4, [0.72, 0.78, 0.86]));

  /* 铰点：底座顶部往上 1 米处 */
  var pivot = Cesium.Matrix4.multiply(
    enu,
    Cesium.Matrix4.fromTranslation(new Cesium.Cartesian3(0, 0, 6)),
    new Cesium.Matrix4()
  );

  Promise.all([
    Cesium.Model.fromGltfAsync({ url: baseUrl, modelMatrix: enu }),
    Cesium.Model.fromGltfAsync({ url: armUrl, modelMatrix: pivot })
  ]).then(function (models) {
    var base = models[0], arm = models[1];
    scene.primitives.add(base);
    scene.primitives.add(arm);

    var rot = new Cesium.Matrix4();
    var m = new Cesium.Matrix4();
    scene.postRender.addEventListener(function () {
      var angle = Math.sin(performance.now() * 0.0012) * 1.1;
      Cesium.Matrix4.fromRotationTranslation(Cesium.Matrix3.fromRotationX(angle), undefined, rot);
      arm.modelMatrix = Cesium.Matrix4.multiply(pivot, rot, m);
    });
  });

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</body>
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