3D Tiles Point Cloud Shading

<!--
  示例：点云的尺寸衰减与明暗
  说明：六千个点的点径随视距变化，亮度按高度递增，左下角显示视距与点径
  核心逻辑：Cartesian3.distance 求视距 → pixelSize 反比衰减 → 高度映射 HSL 亮度
  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>点云的尺寸衰减与明暗</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}
  .hud{position:absolute;left:12px;bottom:12px;z-index:5;background:rgba(23,28,35,.9);
       border:1px solid #2a313b;border-radius:6px;padding:6px 10px;font-size:12px;color:#a2a9b6}
</style>
</head>
<body>
<div id="c"></div>
<div class="tip">缩放视角时左下角的点径数值在变。点的亮度只跟高度有关，越高越亮。</div>
<div id="hud" class="hud">视距 —</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 baseLon = 116.391, baseLat = 39.906;
  var DLON = 1.17e-5, DLAT = 8.98e-6;
  var pc = scene.primitives.add(new Cesium.PointPrimitiveCollection());
  var pts = [];
  var seed = 66;
  function rnd() { seed = (seed * 9301 + 49297) % 233280; return seed / 233280; }

  for (var i = 0; i < 6000; i++) {
    var x = -16 + rnd() * 32, y = -11 + rnd() * 22, z = rnd() * 34;
    var p = pc.add({
      position: Cesium.Cartesian3.fromDegrees(baseLon + x * DLON, baseLat + y * DLAT, z),
      pixelSize: 3,
      color: Cesium.Color.WHITE
    });
    pts.push({ p: p, z: z });
  }

  var center = Cesium.Cartesian3.fromDegrees(baseLon, baseLat, 0);
  var hud = document.getElementById('hud');
  var frame = 0;

  scene.postRender.addEventListener(function () {
    if (frame++ % 5 !== 0) return;
    var d = Cesium.Cartesian3.distance(viewer.camera.positionWC, center);
    /* 点尺寸随视距线性衰减，模拟点云的距离衰减着色 */
    var size = Math.max(1.2, Math.min(9, 9000 / Math.max(d, 60)));
    pts.forEach(function (o) {
      o.p.pixelSize = size;
      /* 亮度按高度：越高越亮，模拟顶光照射 */
      var lv = 0.18 + (o.z / 34) * 0.62;
      o.p.color = Cesium.Color.fromHsl(0.58, 0.22, lv, 0.9);
    });
    hud.textContent = '视距 ' + Math.round(d) + ' 米 · 点径 ' + size.toFixed(1) + ' px';
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3860, 39.9002, 90),
    orientation: { heading: Cesium.Math.toRadians(24), pitch: Cesium.Math.toRadians(-14), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>