Polyline Dash

<!--
  示例：虚线折线
  说明：三条虚线用不同的 dashLength 与颜色，配合流动的虚线表现路径
  核心逻辑：PolylineDashMaterialProperty → dashLength / dashPattern / color
  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>虚线折线</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">dashLength 决定每段实线的像素长度，dashPattern 决定明暗序列。</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 lon = 116.385, lat = 39.902;

  function line(dx, dy, dash, color, gap) {
    var pts = [];
    for (var i = 0; i <= 5; i++) {
      pts.push(lon + dx + i * 0.0011, lat + dy + Math.sin(i) * 0.0012);
    }
    return {
      polyline: {
        positions: Cesium.Cartesian3.fromDegreesArray(pts),
        width: 5,
        material: new Cesium.PolylineDashMaterialProperty({
          color: Cesium.Color.fromCssColorString(color),
          dashLength: dash,
          gapColor: gap ? Cesium.Color.TRANSPARENT : undefined
        })
      }
    };
  }

  viewer.entities.add(line(0, 0, 16, '#4d9bff', false));
  viewer.entities.add(line(0, -0.0030, 32, '#5bb08a', false));
  viewer.entities.add(line(0, -0.0060, 8, '#d08a4e', false));

  /* 让第一条虚线的图案动起来：逐帧改 dashLength */
  var first = viewer.entities.values[0];
  var phase = 0;
  scene.preRender.addEventListener(function () {
    phase = (phase + 0.4) % 64;
    first.polyline.material.dashLength = 16 + phase;
  });
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3905, 39.8965, 620),
    orientation: { heading: Cesium.Math.toRadians(4), pitch: Cesium.Math.toRadians(-26), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>