Clipping Box Model

<!--
  示例：用六个裁剪平面围出一个盒子，剖开模型
  要点：ClippingPlaneCollection 的平面在世界坐标里定义，每个平面保留法线正侧
  依赖：CesiumJS 1.121 · jsDelivr CDN，贴图与 GLB 均由页面生成
-->
<!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>裁剪盒剖切模型</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%}
  .hud{position:absolute;left:12px;top:12px;z-index:5;background:rgba(23,28,35,.92);
       border:1px solid #2a313b;border-radius:6px;padding:9px 12px;font-size:12px;
       color:#a2a9b6;width:252px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:7px}
  input[type=range]{width:100%}
  .hud button{font:inherit;font-size:12px;padding:3px 9px;border-radius:4px;cursor:pointer;
       border:1px solid #343b46;background:#1d232b;color:#cfd6e2;margin-top:8px}
  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}
</style>
</head>
<body>
<div id="c"></div>
<div class="hud">
  <div><b>裁剪盒</b></div>
  <div class="row">盒半径 <span id="hVal">110</span> 米</div>
  <div class="row"><input id="half" type="range" min="40" max="140" step="5" value="110"></div>
  <div class="row" id="info">六个平面同时生效</div>
  <div class="row"><button id="flip">反向裁剪</button></div>
</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;

  var CENTER = Cesium.Cartesian3.fromDegrees(116.389, 39.906, 300);
  var MATRIX = Cesium.Transforms.eastNorthUpToFixedFrame(CENTER);

  /* ---------- 贴图：斜条纹 + 分区色块 ---------- */
  function drawTexture() {
    var c = document.createElement('canvas');
    c.width = c.height = 256;
    var ctx = c.getContext('2d');
    ctx.fillStyle = '#22405c';
    ctx.fillRect(0, 0, 256, 256);

    ctx.strokeStyle = 'rgba(122,182,255,0.85)';
    ctx.lineWidth = 10;
    for (var i = -256; i < 512; i += 48) {
      ctx.beginPath();
      ctx.moveTo(i, 0);
      ctx.lineTo(i + 256, 256);
      ctx.stroke();
    }

    ctx.fillStyle = 'rgba(255,177,61,0.75)';
    ctx.fillRect(0, 0, 256, 56);
    ctx.fillStyle = 'rgba(95,208,168,0.6)';
    ctx.fillRect(0, 200, 256, 56);
    return c.toDataURL('image/png');
  }

  function pngBytes(dataUrl) {
    var raw = atob(dataUrl.split(',')[1]);
    var bytes = new Uint8Array(raw.length);
    for (var i = 0; i < raw.length; i++) bytes[i] = raw.charCodeAt(i);
    return bytes;
  }

  /* ---------- 带 UV 的立方体 ---------- */
  function buildCube() {
    var faces = [
      { n: [0, 0, 1],  v: [[-1, -1, 1], [1, -1, 1], [1, 1, 1], [-1, 1, 1]] },
      { n: [0, 0, -1], v: [[1, -1, -1], [-1, -1, -1], [-1, 1, -1], [1, 1, -1]] },
      { n: [1, 0, 0],  v: [[1, -1, 1], [1, -1, -1], [1, 1, -1], [1, 1, 1]] },
      { n: [-1, 0, 0], v: [[-1, -1, -1], [-1, -1, 1], [-1, 1, 1], [-1, 1, -1]] },
      { n: [0, 1, 0],  v: [[-1, 1, 1], [1, 1, 1], [1, 1, -1], [-1, 1, -1]] },
      { n: [0, -1, 0], v: [[-1, -1, -1], [1, -1, -1], [1, -1, 1], [-1, -1, 1]] }
    ];
    var uv = [[0, 1], [1, 1], [1, 0], [0, 0]];
    var pos = [], nrm = [], tex = [], idx = [];
    faces.forEach(function (f, fi) {
      f.v.forEach(function (p, vi) {
        pos.push(p[0] * 0.5, p[1] * 0.5, p[2] * 0.5);
        nrm.push(f.n[0], f.n[1], f.n[2]);
        tex.push(uv[vi][0], uv[vi][1]);
      });
      var b = fi * 4;
      idx.push(b, b + 1, b + 2, b, b + 2, b + 3);
    });
    return {
      pos: new Float32Array(pos),
      nrm: new Float32Array(nrm),
      uv: new Float32Array(tex),
      idx: new Uint16Array(idx)
    };
  }

  function buildGlb(gltf, chunks) {
    var len = 0;
    chunks.forEach(function (c) { len += c.data.byteLength; });
    var bin = new Uint8Array(len);
    var offset = 0;
    gltf.bufferViews = chunks.map(function (c) {
      var view = { buffer: 0, byteOffset: offset, byteLength: c.data.byteLength };
      if (c.target) view.target = c.target;
      bin.set(new Uint8Array(c.data.buffer, c.data.byteOffset, c.data.byteLength), offset);
      offset += c.data.byteLength;
      return view;
    });
    gltf.buffers = [{ byteLength: len }];

    var json = new TextEncoder().encode(JSON.stringify(gltf));
    var jsonPad = (4 - json.length % 4) % 4;
    var binPad = (4 - len % 4) % 4;
    var total = 12 + 8 + json.length + jsonPad + 8 + len + binPad;
    var out = new Uint8Array(total);
    var dv = new DataView(out.buffer);
    dv.setUint32(0, 0x46546C67, true);
    dv.setUint32(4, 2, true);
    dv.setUint32(8, total, true);
    dv.setUint32(12, json.length + jsonPad, true);
    dv.setUint32(16, 0x4E4F534A, true);
    out.set(json, 20);
    for (var i = 0; i < jsonPad; i++) out[20 + json.length + i] = 0x20;
    var p = 20 + json.length + jsonPad;
    dv.setUint32(p, len + binPad, true);
    dv.setUint32(p + 4, 0x004E4942, true);
    out.set(bin, p + 8);
    return out;
  }

  var geo = buildCube();
  var png = pngBytes(drawTexture());

  var gltf = {
    asset: { version: '2.0' },
    scene: 0,
    scenes: [{ nodes: [0] }],
    nodes: [{ mesh: 0 }],
    meshes: [{
      primitives: [{
        attributes: { POSITION: 0, NORMAL: 1, TEXCOORD_0: 2 },
        indices: 3,
        material: 0
      }]
    }],
    images: [{ bufferView: 4, mimeType: 'image/png' }],
    samplers: [{ magFilter: 9729, minFilter: 9729, wrapS: 10497, wrapT: 10497 }],
    textures: [{ sampler: 0, source: 0 }],
    materials: [{
      pbrMetallicRoughness: {
        baseColorTexture: { index: 0 },
        metallicFactor: 0.2,
        roughnessFactor: 0.6
      },
      doubleSided: true
    }],
    accessors: [
      { bufferView: 0, componentType: 5126, count: 24, type: 'VEC3',
        min: [-0.5, -0.5, -0.5], max: [0.5, 0.5, 0.5] },
      { bufferView: 1, componentType: 5126, count: 24, type: 'VEC3' },
      { bufferView: 2, componentType: 5126, count: 24, type: 'VEC2' },
      { bufferView: 3, componentType: 5123, count: 36, type: 'SCALAR' }
    ]
  };

  var glb = buildGlb(gltf, [
    { data: geo.pos, target: 34962 },
    { data: geo.nrm, target: 34962 },
    { data: geo.uv, target: 34962 },
    { data: geo.idx, target: 34963 },
    { data: png }
  ]);

  var url = URL.createObjectURL(new Blob([glb], { type: 'model/gltf-binary' }));
  var model = null;

  /* 由局部轴向与偏移量算出世界坐标下的平面 */
  var axis = new Cesium.Cartesian3();

  function plane(nx, ny, nz, offsetMeters, keepPositive) {
    axis = Cesium.Cartesian3.fromElements(nx, ny, nz, axis);
    var nWorld = Cesium.Matrix4.multiplyByPointAsVector(
      MATRIX, axis, new Cesium.Cartesian3()
    );
    Cesium.Cartesian3.normalize(nWorld, nWorld);
    if (!keepPositive) Cesium.Cartesian3.negate(nWorld, nWorld);

    var pWorld = Cesium.Matrix4.multiplyByPoint(
      MATRIX,
      new Cesium.Cartesian3(nx * offsetMeters, ny * offsetMeters, nz * offsetMeters),
      new Cesium.Cartesian3()
    );
    return new Cesium.ClippingPlane(nWorld, -Cesium.Cartesian3.dot(nWorld, pWorld));
  }

  var inward = true;

  function buildCollection(half) {
    /* keepPositive 取反就能把「保留盒内」变成「保留盒外」 */
    var sign = inward;
    return new Cesium.ClippingPlaneCollection({
      /* 保留盒外时，六个平面围出的被裁区域要取并集 */
      unionClippingRegions: !inward,
      planes: [
        plane(1, 0, 0, half, !sign),
        plane(-1, 0, 0, half, !sign),
        plane(0, 1, 0, half, !sign),
        plane(0, -1, 0, half, !sign),
        plane(0, 0, 1, half, !sign),
        plane(0, 0, -1, half, !sign)
      ],
      edgeWidth: 2.0,
      edgeColor: Cesium.Color.fromCssColorString('#ffb13d')
    });
  }

  Cesium.Model.fromGltfAsync({ url: url, scale: 220 }).then(function (m) {
    m.modelMatrix = MATRIX;
    m.backFaceCulling = false;
    if (m.clippingPlanesOriginMatrix) {
      m.clippingPlanesOriginMatrix = Cesium.Matrix4.IDENTITY;
    }
    scene.primitives.add(m);
    model = m;
    m.clippingPlanes = buildCollection(110);
    document.getElementById('info').textContent = '盒半径 110 米 · 保留盒内';
  }).catch(function (err) {
    document.getElementById('info').textContent = '解析失败：' + err.message;
  });

  document.getElementById('half').addEventListener('input', function () {
    var h = parseInt(this.value, 10);
    document.getElementById('hVal').textContent = h;
    if (model) model.clippingPlanes = buildCollection(h);
  });

  document.getElementById('flip').addEventListener('click', function () {
    inward = !inward;
    var h = parseInt(document.getElementById('half').value, 10);
    if (model) model.clippingPlanes = buildCollection(h);
    document.getElementById('info').textContent = inward
      ? '盒半径 ' + h + ' 米 · 保留盒内' : '盒半径 ' + h + ' 米 · 保留盒外';
    this.textContent = inward ? '反向裁剪' : '恢复盒内';
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.397, 39.898, 620),
    orientation: {
      heading: Cesium.Math.toRadians(40),
      pitch: Cesium.Math.toRadians(-18),
      roll: 0
    },
    duration: 0
  });
})();
</script>
</body>
</html>