Clipping Regions

<!--
  示例：用多边形裁剪区域只保留一块地表
  说明：ClippingPolygonCollection 把球体裁成多边形柱体范围，范围外的地表不渲染
  核心逻辑：new ClippingPolygon + new ClippingPolygonCollection → globe.clippingPolygons
  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>多边形裁剪区域</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,.9);
       border:1px solid #2a313b;border-radius:6px;padding:9px 12px;font-size:12px;
       color:#a2a9b6;max-width:260px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:7px}
  .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>多边形裁剪</b></div>
  <div class="row">只保留六边形柱体内的地表</div>
  <div class="row"><label><input id="on" type="checkbox" checked> 启用裁剪</label></div>
  <div class="row"><label><input id="inv" type="checkbox"> 内外反转</label></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('#2a3a4d');
  scene.backgroundColor = Cesium.Color.fromCssColorString('#070b10');
  scene.skyBox.show = false;
  scene.sun.show = false;
  scene.moon.show = false;
  if (scene.skyAtmosphere) scene.skyAtmosphere.show = false;

  /* 围绕北京画一个六边形，作为保留区域 */
  function hexagon(centerLon, centerLat, radiusDeg) {
    var arr = [];
    for (var i = 0; i < 6; i++) {
      var a = Math.PI / 6 + i * Math.PI / 3;
      arr.push(centerLon + radiusDeg * Math.cos(a));
      arr.push(centerLat + radiusDeg * 0.75 * Math.sin(a));
    }
    return arr;
  }

  var ring = hexagon(116.3913, 39.9074, 2.4);
  var polygon = new Cesium.ClippingPolygon({
    positions: Cesium.Cartesian3.fromDegreesArray(ring)
  });

  function apply(inverse) {
    scene.globe.clippingPolygons = new Cesium.ClippingPolygonCollection({
      polygons: [polygon],
      inverse: inverse
    });
  }

  apply(false);

  /* 边界线，用来看清裁剪范围 */
  var outline = [];
  for (var i = 0; i < ring.length; i += 2) {
    outline.push(ring[i], ring[i + 1]);
  }
  outline.push(ring[0], ring[1]);

  viewer.entities.add({
    polyline: {
      positions: Cesium.Cartesian3.fromDegreesArray(outline),
      width: 2,
      clampToGround: true,
      material: Cesium.Color.fromCssColorString('#ffd166')
    }
  });

  viewer.entities.add({
    position: Cesium.Cartesian3.fromDegrees(116.3913, 39.9074, 0),
    point: {
      pixelSize: 10,
      color: Cesium.Color.fromCssColorString('#4d9bff'),
      outlineColor: Cesium.Color.WHITE,
      outlineWidth: 2,
      disableDepthTestDistance: Number.POSITIVE_INFINITY
    }
  });

  document.getElementById('on').addEventListener('change', function () {
    if (this.checked) {
      apply(document.getElementById('inv').checked);
    } else {
      scene.globe.clippingPolygons = undefined;
    }
  });

  document.getElementById('inv').addEventListener('change', function () {
    if (document.getElementById('on').checked) apply(this.checked);
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3913, 39.9074, 1300000),
    orientation: {
      heading: 0,
      pitch: Cesium.Math.toRadians(-62),
      roll: 0
    },
    duration: 0
  });
})();
</script>
</body>
</html>