Imagery Layers

<!--
  示例：叠加多个影像图层
  说明：底图、半透明专题层与小范围标注层依次叠加，层级可调
  核心逻辑：SingleTileImageryProvider 生成图层 → imageryLayers.add → 调整 alpha 与顺序
  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>叠加多个影像图层</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">三层影像叠在一起：底层是灰蓝底图，中层半透明，顶层只覆盖一小块。</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 makeImage(w, h, draw) {
    var c = document.createElement('canvas');
    c.width = w; c.height = h;
    draw(c.getContext('2d'), w, h);
    return c.toDataURL('image/png');
  }

  var rect = Cesium.Rectangle.fromDegrees(115.8, 39.4, 117.0, 40.4);

  /* 底层：网格底图 */
  var base = viewer.imageryLayers.addImageryProvider(
    new Cesium.SingleTileImageryProvider({
      url: makeImage(512, 512, function (ctx, w, h) {
        ctx.fillStyle = '#1b2634'; ctx.fillRect(0, 0, w, h);
        ctx.strokeStyle = 'rgba(90,120,155,0.35)';
        for (var x = 0; x < w; x += 32) {
          ctx.beginPath(); ctx.moveTo(x, 0); ctx.lineTo(x, h); ctx.stroke();
        }
      }),
      rectangle: rect
    })
  );

  /* 中层：半透明的热区 */
  var overlay = viewer.imageryLayers.addImageryProvider(
    new Cesium.SingleTileImageryProvider({
      url: makeImage(512, 512, function (ctx, w, h) {
        var g = ctx.createRadialGradient(w * 0.6, h * 0.4, 10, w * 0.6, h * 0.4, w * 0.4);
        g.addColorStop(0, 'rgba(255,150,60,0.95)');
        g.addColorStop(1, 'rgba(255,150,60,0)');
        ctx.fillStyle = g; ctx.fillRect(0, 0, w, h);
      }),
      rectangle: rect
    })
  );
  overlay.alpha = 0.65;

  /* 顶层：只覆盖右上角的小图块 */
  var patch = viewer.imageryLayers.addImageryProvider(
    new Cesium.SingleTileImageryProvider({
      url: makeImage(256, 256, function (ctx, w, h) {
        ctx.fillStyle = '#2f6f5e'; ctx.fillRect(0, 0, w, h);
        ctx.strokeStyle = '#8fd3c0'; ctx.lineWidth = 4;
        ctx.strokeRect(8, 8, w - 16, h - 16);
      }),
      rectangle: Cesium.Rectangle.fromDegrees(116.3, 39.9, 116.7, 40.2)
    })
  );

  /* 调整顺序：把标注层提到最上 */
  viewer.imageryLayers.raise(patch);
  viewer.camera.flyTo({
    destination: Cesium.Rectangle.fromDegrees(115.8, 39.4, 117.0, 40.4),
    duration: 0
  });
})();
</script>
</body>
</html>