Clouds

<!--
  示例：程序化云层
  说明：一百多片云在八千米高度缓慢漂移，形成连续云带
  核心逻辑：canvas 云团贴图 → BillboardCollection → 逐帧偏移经度
  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>程序化云层</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">云是很多张半透明贴图叠出来的，每片的尺寸与透明度都不同。</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 puff() {
    var c = document.createElement('canvas');
    c.width = c.height = 128;
    var ctx = c.getContext('2d');
    for (var i = 0; i < 26; i++) {
      var x = 32 + Math.random() * 64, y = 40 + Math.random() * 48;
      var r = 12 + Math.random() * 22;
      var g = ctx.createRadialGradient(x, y, 0, x, y, r);
      g.addColorStop(0, 'rgba(255,255,255,0.42)');
      g.addColorStop(1, 'rgba(255,255,255,0)');
      ctx.fillStyle = g;
      ctx.beginPath(); ctx.arc(x, y, r, 0, Math.PI * 2); ctx.fill();
    }
    return c.toDataURL('image/png');
  }

  var texture = puff();
  var clouds = new Cesium.BillboardCollection({ scene: scene });
  scene.primitives.add(clouds);

  var items = [];
  for (var i = 0; i < 130; i++) {
    var b = clouds.add({
      position: Cesium.Cartesian3.fromDegrees(
        116.30 + Math.random() * 0.20, 39.80 + Math.random() * 0.16, 7600 + Math.random() * 1400
      ),
      image: texture,
      scale: 900 + Math.random() * 1400,
      color: Cesium.Color.fromCssColorString('#dfe8f2').withAlpha(0.5 + Math.random() * 0.3)
    });
    items.push(b);
  }

  scene.preRender.addEventListener(function () {
    for (var i = 0; i < items.length; i++) {
      var p = items[i].position;
      var carto = Cesium.Cartographic.fromCartesian(p);
      items[i].position = Cesium.Cartesian3.fromRadians(
        carto.longitude + 0.0000022, carto.latitude, carto.height
      );
    }
  });
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3895, 39.8680, 5400),
    orientation: { heading: 0, pitch: Cesium.Math.toRadians(-2), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>