Render Mode

<!--
  示例：静止场景下不再逐帧重绘
  要点：requestRenderMode 打开后，只有相机变化或调用 requestRender 才渲染
  依赖：CesiumJS 1.121 · jsDelivr CDN，无外部资源
-->
<!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>按需渲染</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,.92);
       border:1px solid #2a313b;border-radius:6px;padding:9px 12px;font-size:12px;
       color:#a2a9b6;width:256px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:7px}
  .hud button{font:inherit;font-size:12px;padding:3px 9px;margin-right:4px;border-radius:4px;
       cursor:pointer;border:1px solid #343b46;background:#1d232b;color:#cfd6e2}
  .hud button.on{background:#1d3a5c;border-color:#3d6f9e;color:#cfe4ff}
  .mono{font-family:ui-monospace,Consolas,monospace;font-size:11px;color:#8fb7e0}
  .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>按需渲染</b></div>
  <div class="row">
    <button id="on" class="on">开启</button>
    <button id="off">关闭</button>
    <button id="once">手动重绘</button>
  </div>
  <div class="row mono" id="cnt">累计渲染 0 帧</div>
  <div class="row">不动鼠标时帧数不再增长</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;

  /* 静态内容：一片楼群，不随时间变化 */
  for (var i = 0; i < 6; i++) {
    for (var j = 0; j < 4; j++) {
      var h = 120 + ((i + j) % 3) * 90;
      viewer.entities.add({
        position: Cesium.Cartesian3.fromDegrees(
          116.372 + i * 0.008, 39.898 + j * 0.008, h / 2
        ),
        box: {
          dimensions: new Cesium.Cartesian3(180, 180, h),
          material: Cesium.Color.fromCssColorString(
            (i + j) % 2 === 0 ? '#2c4a6b' : '#354f63'
          ),
          outline: true,
          outlineColor: Cesium.Color.fromCssColorString('#7fa6c9')
        }
      });
    }
  }

  /* 打开按需渲染：maximumRenderTimeChange 设为无穷，静止时彻底不画 */
  scene.requestRenderMode = true;
  scene.maximumRenderTimeChange = Number.POSITIVE_INFINITY;

  var frames = 0;
  scene.postRender.addEventListener(function () {
    frames++;
  });

  /* 用定时器更新文字，不触发 Cesium 渲染 */
  setInterval(function () {
    document.getElementById('cnt').textContent = '累计渲染 ' + frames + ' 帧';
  }, 400);

  document.getElementById('on').addEventListener('click', function () {
    scene.requestRenderMode = true;
    scene.maximumRenderTimeChange = Number.POSITIVE_INFINITY;
    this.className = 'on';
    document.getElementById('off').className = '';
  });

  document.getElementById('off').addEventListener('click', function () {
    scene.requestRenderMode = false;
    this.className = 'on';
    document.getElementById('on').className = '';
  });

  document.getElementById('once').addEventListener('click', function () {
    scene.requestRender();
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.364, 39.886, 1900),
    orientation: {
      heading: Cesium.Math.toRadians(26),
      pitch: Cesium.Math.toRadians(-30),
      roll: 0
    },
    duration: 0
  });
})();
</script>
</body>
</html>