Gltf PBR Extensions

<!--
  示例：glTF PBR 扩展
  说明：同一模型分别启用清漆与高光扩展，表面反射质感明显不同
  核心逻辑：KHR_materials_clearcoat / KHR_materials_specular → extensionsUsed 声明
  依赖：CesiumJS 1.121 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>glTF PBR 扩展</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Widgets/widgets.css">
<style>
  html,body{height:100%;margin:0}
  body{background:#0e1116;color:#e6e8ec;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  #c{height:100%}
  .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:320px;line-height:1.6}

  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}
</style>
</head>
<body>
<div id="c"></div>
<div class="tip">左边的模型加了清漆层，高光更集中；右边是普通材质。</div>
<script src="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Cesium.js"></script>
<script>
(function () {
  'use strict';

  var viewer = new Cesium.Viewer('c', {
    baseLayer: false,
    baseLayerPicker: false, geocoder: false, homeButton: false,
    sceneModePicker: false, navigationHelpButton: false,
    animation: false, timeline: false, fullscreenButton: false,
    infoBox: false, selectionIndicator: false
  });

  var scene = viewer.scene;
  scene.globe.baseColor = Cesium.Color.fromCssColorString('#1c2733');
  scene.backgroundColor = Cesium.Color.fromCssColorString('#0e1116');
  scene.skyBox.show = false;
  scene.sun.show = false;
  scene.moon.show = false;
  if (scene.skyAtmosphere) scene.skyAtmosphere.show = false;

  function glbBytes(json, bin) {
    var jb = new TextEncoder().encode(JSON.stringify(json));
    var jpad = (4 - jb.length % 4) % 4, bpad = (4 - bin.length % 4) % 4;
    var jl = jb.length + jpad, bl = bin.length + bpad;
    var out = new Uint8Array(12 + 8 + jl + 8 + bl), dv = new DataView(out.buffer);
    dv.setUint32(0, 0x46546c67, true); dv.setUint32(4, 2, true); dv.setUint32(8, out.length, true);
    dv.setUint32(12, jl, true); dv.setUint32(16, 0x4e4f534a, true); out.set(jb, 20);
    for (var i = 0; i < jpad; i++) out[20 + jb.length + i] = 0x20;
    dv.setUint32(20 + jl, bl, true); dv.setUint32(24 + jl, 0x004e4942, true); out.set(bin, 28 + jl);
    return out;
  }

  function sphereish(kind) {
    /* 用盒体代表外壳，重点是材质扩展本身 */
    var hx = 22, hz = 22, h = 44;
    var faces = [
      [[hx, 0, hz], [hx, 0, -hz], [hx, h, -hz], [hx, h, hz], [1, 0, 0]],
      [[-hx, 0, -hz], [-hx, 0, hz], [-hx, h, hz], [-hx, h, -hz], [-1, 0, 0]],
      [[-hx, h, hz], [hx, h, hz], [hx, h, -hz], [-hx, h, -hz], [0, 1, 0]],
      [[-hx, 0, -hz], [hx, 0, -hz], [hx, 0, hz], [-hx, 0, hz], [0, -1, 0]],
      [[-hx, 0, hz], [hx, 0, hz], [hx, h, hz], [-hx, h, hz], [0, 0, 1]],
      [[hx, 0, -hz], [-hx, 0, -hz], [-hx, h, -hz], [hx, h, -hz], [0, 0, -1]]
    ];
    var pos = [], nor = [], idx = [], base = 0;
    faces.forEach(function (f) {
      for (var i = 0; i < 4; i++) { pos.push(f[i][0], f[i][1], f[i][2]); 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;
    });
    var p = new Float32Array(pos), n = new Float32Array(nor), ix = new Uint16Array(idx);
    var pb = p.byteLength, nb = n.byteLength, ib = ix.byteLength;
    var bin = new Uint8Array(pb + nb + ib);
    bin.set(new Uint8Array(p.buffer), 0);
    bin.set(new Uint8Array(n.buffer), pb);
    bin.set(new Uint8Array(ix.buffer), pb + nb);

    var material = {
      pbrMetallicRoughness: {
        baseColorFactor: [0.28, 0.42, 0.58, 1], metallicFactor: 0.0, roughnessFactor: 0.25
      }
    };
    var usage = [];
    if (kind === 'clearcoat') {
      material.extensions = { KHR_materials_clearcoat: { clearcoatFactor: 1.0, clearcoatRoughnessFactor: 0.05 } };
      usage.push('KHR_materials_clearcoat');
    }
    if (kind === 'specular') {
      material.extensions = { KHR_materials_specular: { specularFactor: 1.0, specularColorFactor: [1.0, 0.85, 0.6] } };
      usage.push('KHR_materials_specular');
    }

    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: [material],
      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' }
      ],
      bufferViews: [
        { buffer: 0, byteOffset: 0, byteLength: pb, target: 34962 },
        { buffer: 0, byteOffset: pb, byteLength: nb, target: 34962 },
        { buffer: 0, byteOffset: pb + nb, byteLength: ib, target: 34963 }
      ],
      buffers: [{ byteLength: pb + nb + ib }]
    };
    if (usage.length) json.extensionsUsed = usage;
    return new Blob([glbBytes(json, bin)], { type: 'model/gltf-binary' });
  }

  function place(kind, lon) {
    var enu = Cesium.Transforms.eastNorthUpToFixedFrame(
      Cesium.Cartesian3.fromDegrees(lon, 39.9035, 0)
    );
    Cesium.Model.fromGltfAsync({
      url: URL.createObjectURL(sphereish(kind)),
      modelMatrix: enu
    }).then(function (model) { scene.primitives.add(model); });
  }

  place('none', 116.3862);
  place('clearcoat', 116.3895);
  place('specular', 116.3928);
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3895, 39.8988, 200),
    orientation: { heading: Cesium.Math.toRadians(4), pitch: Cesium.Math.toRadians(-8), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>