Drawing on Terrain

<!--
  示例：在地面上绘制多边形
  说明：左键依次落点，右键清空重画，落点实时连成面
  核心逻辑：LEFT_CLICK 拾取椭球交点 → CallbackProperty 动态 hierarchy → RIGHT_CLICK 清空
  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>在地面上绘制多边形</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">左键点几下就围出一个面，右键清空重新开始。</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 points = [];

  /* 动态几何：每次渲染时读取当前点集 */
  var polygon = viewer.entities.add({
    polygon: {
      hierarchy: new Cesium.CallbackProperty(function () {
        return new Cesium.PolygonHierarchy(points.slice());
      }, false),
      height: 0,
      material: Cesium.Color.fromCssColorString('#4d9bff').withAlpha(0.35)
    }
  });

  var outline = viewer.entities.add({
    polyline: {
      positions: new Cesium.CallbackProperty(function () {
        return points.length > 1 ? points.concat([points[0]]) : [];
      }, false),
      width: 2,
      material: Cesium.Color.fromCssColorString('#cfe2f5')
    }
  });

  var handler = new Cesium.ScreenSpaceEventHandler(scene.canvas);
  handler.setInputAction(function (click) {
    var cartesian = viewer.camera.pickEllipsoid(click.position, Cesium.Ellipsoid.WGS84);
    if (!Cesium.defined(cartesian)) return;
    points.push(cartesian);
  }, Cesium.ScreenSpaceEventType.LEFT_CLICK);

  handler.setInputAction(function () {
    points.length = 0;
  }, Cesium.ScreenSpaceEventType.RIGHT_CLICK);
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.390, 39.8975, 1400),
    orientation: { heading: 0, pitch: Cesium.Math.toRadians(-38), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>