Appearance Translucent

<!--
  示例：半透明盒体与不透明盒体的外观对比
  要点：PerInstanceColorAppearance 的 translucent 与 closed 决定混合方式和背面剔除
  依赖：CesiumJS 1.121 · jsDelivr CDN，几何由 BoxGeometry 生成
-->
<!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>半透明外观</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:250px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:6px}
  .hud button{font:inherit;font-size:12px;padding:3px 9px;border-radius:4px;cursor:pointer;
       border:1px solid #343b46;background:#1d232b;color:#cfd6e2}
  .hud button.on{background:#1d3a5c;border-color:#3d6f9e;color:#cfe4ff}
  .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>外观对比</b></div>
  <div class="row">
    <button id="btnA" class="on">半透明</button>
    <button id="btnB">不透明</button>
  </div>
  <div class="row" id="info">alpha 0.38 · closed false</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('#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 BOXES = [
    { lng: 116.380, lat: 39.906, size: [180, 180, 260], color: '#4d9bff' },
    { lng: 116.390, lat: 39.903, size: [180, 180, 180], color: '#5fd0a8' },
    { lng: 116.398, lat: 39.909, size: [180, 180, 330], color: '#ffb13d' }
  ];

  /* 一组实例，颜色写在逐实例属性里，外观决定怎么混合 */
  function makeInstances(alpha) {
    return BOXES.map(function (b) {
      return new Cesium.GeometryInstance({
        geometry: Cesium.BoxGeometry.fromDimensions({
          dimensions: new Cesium.Cartesian3(b.size[0], b.size[1], b.size[2]),
          vertexFormat: Cesium.PerInstanceColorAppearance.VERTEX_FORMAT
        }),
        modelMatrix: Cesium.Transforms.eastNorthUpToFixedFrame(
          Cesium.Cartesian3.fromDegrees(b.lng, b.lat, b.size[2] / 2)
        ),
        attributes: {
          color: Cesium.ColorGeometryInstanceAttribute.fromColor(
            Cesium.Color.fromCssColorString(b.color).withAlpha(alpha)
          )
        }
      });
    });
  }

  var translucentPrimitive = new Cesium.Primitive({
    geometryInstances: makeInstances(0.38),
    appearance: new Cesium.PerInstanceColorAppearance({
      translucent: true,
      closed: false,
      flat: false
    })
  });

  var opaquePrimitive = new Cesium.Primitive({
    geometryInstances: makeInstances(1.0),
    appearance: new Cesium.PerInstanceColorAppearance({
      translucent: false,
      closed: true,
      flat: false
    })
  });

  scene.primitives.add(opaquePrimitive);
  scene.primitives.add(translucentPrimitive);
  opaquePrimitive.show = false;

  /* 立在盒体后方的一块深色底板，透过半透明盒体可以看到它 */
  viewer.entities.add({
    position: Cesium.Cartesian3.fromDegrees(116.389, 39.920, 120),
    box: {
      dimensions: new Cesium.Cartesian3(3200, 120, 240),
      material: Cesium.Color.fromCssColorString('#5b6573')
    }
  });

  var btnA = document.getElementById('btnA');
  var btnB = document.getElementById('btnB');
  var info = document.getElementById('info');

  function show(mode) {
    var trans = mode === 'translucent';
    translucentPrimitive.show = trans;
    opaquePrimitive.show = !trans;
    btnA.className = trans ? 'on' : '';
    btnB.className = trans ? '' : 'on';
    info.textContent = trans
      ? 'alpha 0.38 · closed false · 背面可见'
      : 'alpha 1.0 · closed true · 背面剔除';
  }

  btnA.addEventListener('click', function () { show('translucent'); });
  btnB.addEventListener('click', function () { show('opaque'); });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.374, 39.897, 1550),
    orientation: {
      heading: Cesium.Math.toRadians(22),
      pitch: Cesium.Math.toRadians(-26),
      roll: 0
    },
    duration: 0
  });
})();
</script>
</body>
</html>