Fog Post Process

<!--
  示例：自定义雾效后处理
  说明：用深度贴图算视距，越远的楼体越接近雾色，近处保持清晰
  核心逻辑：PostProcessStage + depthTexture → czm_windowToEyeCoordinates 求视距 → 指数衰减混色
  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>自定义雾效后处理</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">雾的浓度由 density 控制，越远越白。楼体成排后退，距离层次一眼可见。</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;

  /* 一排由近及远的楼，雾的层次才看得出来 */
  for (var i = 0; i < 26; i++) {
    var d = i * 0.0022;
    viewer.entities.add({
      position: Cesium.Cartesian3.fromDegrees(116.3880 + d, 39.9065, 20 + i * 1.5),
      box: {
        dimensions: new Cesium.Cartesian3(14, 14, 40 + i * 3),
        material: Cesium.Color.fromCssColorString('#61758f')
      }
    });
  }

  var fog = scene.postProcessStages.add(new Cesium.PostProcessStage({
    uniforms: {
      density: 0.0022,
      fogColor: new Cesium.Cartesian3(0.62, 0.68, 0.76)
    },
    fragmentShader: [
      'uniform sampler2D colorTexture;',
      'uniform sampler2D depthTexture;',
      'uniform float density;',
      'uniform vec3 fogColor;',
      'in vec2 v_textureCoordinates;',
      'void main() {',
      '  vec4 color = texture(colorTexture, v_textureCoordinates);',
      '  float depth = czm_readDepth(depthTexture, v_textureCoordinates);',
      '  vec3 eye = czm_windowToEyeCoordinates(vec4(gl_FragCoord.xy, depth, 1.0)).xyz;',
      '  float dist = length(eye);',
      '  float f = 1.0 - exp(-density * dist);',
      '  f = clamp(f, 0.0, 0.82);',
      '  out_FragColor = vec4(mix(color.rgb, fogColor, f), color.a);',
      '}'
    ].join('\n')
  }));
  fog.enabled = true;
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3920, 39.9008, 60),
    orientation: { heading: Cesium.Math.toRadians(18), pitch: Cesium.Math.toRadians(-5), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>