Webgl Shaded Relief

<!--
  示例：OpenLayers WebGL 山体阴影
  要点：Terrarium 高程经 WebGL 表达式计算坡度与坡向，实时生成山体阴影
  依赖：OpenLayers 10.3.1 · 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>WebGL 山体阴影</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar select,.bar input[type=range]{font-size:12px}
  .bar .val{font-family:ui-monospace,Consolas,monospace;color:#1f5fd0;min-width:44px}
  .bar .sep{width:1px;height:16px;background:#d8dce2}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>垂直夸张 <input type="range" id="vert" min="0.5" max="3" step="0.1" value="1.2"><span class="val" id="vertOut">1.2</span></label>
  <label>太阳高度 <input type="range" id="sunEl" min="5" max="85" value="45"><span class="val" id="sunElOut">45°</span></label>
  <label>太阳方位 <input type="range" id="sunAz" min="0" max="360" value="315"><span class="val" id="sunAzOut">315°</span></label>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net';
    return;
  }


  var demGrid = ol.tilegrid.createXYZ({tileSize: 256, maxZoom: 12});
  var size = 256;

  function elevationAt(lon, lat) {
    var hills =
      520 * Math.exp(-(Math.pow(lon - 115.55, 2) + Math.pow(lat - 39.95, 2)) / 0.09) +
      360 * Math.exp(-(Math.pow(lon - 116.05, 2) + Math.pow(lat - 40.25, 2)) / 0.05) +
      300 * Math.exp(-(Math.pow(lon - 115.85, 2) + Math.pow(lat - 39.35, 2)) / 0.06);
    var folds = 85 * Math.sin(lon * 32 + lat * 6) * Math.cos(lat * 29) +
      38 * Math.sin(lon * 78 + lat * 21) * Math.cos(lat * 66);
    var valley = -240 * Math.exp(-Math.pow((lon - 116.2) / 0.07, 2)) *
      Math.exp(-Math.pow((lat - 39.9) / 0.35, 2));
    return 180 + hills + folds + valley;
  }

  var terrain = new ol.source.DataTile({
    tileGrid: demGrid,
    projection: 'EPSG:3857',
    transition: 0,
    wrapX: true,
    loader: function (z, x, y) {
      var extent = demGrid.getTileCoordExtent([z, x, y]);
      var resolution = demGrid.getResolution(z);
      var data = new Uint8Array(size * size * 3);
      var offset = 0;
      for (var row = 0; row < size; ++row) {
        var mapY = extent[3] - (row + 0.5) * resolution;
        for (var col = 0; col < size; ++col) {
          var mapX = extent[0] + (col + 0.5) * resolution;
          var lonlat = ol.proj.toLonLat([mapX, mapY]);
          var height = elevationAt(lonlat[0], lonlat[1]);
          var value = Math.max(0, Math.round((height + 32768) * 256));
          data[offset] = Math.floor(value / 65536) % 256;
          data[offset + 1] = Math.floor(value / 256) % 256;
          data[offset + 2] = value % 256;
          offset += 3;
        }
      }
      return data;
    }
  });

  function elevation(xOffset, yOffset) {
    return [
      '+',
      ['*', 255 * 256, ['band', 1, xOffset, yOffset]],
      ['*', 255, ['band', 2, xOffset, yOffset]],
      ['*', 255 / 256, ['band', 3, xOffset, yOffset]],
      -32768
    ];
  }

  var dp = ['*', 2, ['resolution']];
  var z0x = ['*', ['var', 'vert'], elevation(-1, 0)];
  var z1x = ['*', ['var', 'vert'], elevation(1, 0)];
  var dzdx = ['/', ['-', z1x, z0x], dp];
  var z0y = ['*', ['var', 'vert'], elevation(0, -1)];
  var z1y = ['*', ['var', 'vert'], elevation(0, 1)];
  var dzdy = ['/', ['-', z1y, z0y], dp];
  var slope = ['atan', ['sqrt', ['+', ['^', dzdx, 2], ['^', dzdy, 2]]]];
  var aspect = ['clamp', ['atan', ['-', 0, dzdx], dzdy], -Math.PI, Math.PI];
  var sunEl = ['*', Math.PI / 180, ['var', 'sunEl']];
  var sunAz = ['*', Math.PI / 180, ['var', 'sunAz']];
  var cosIncidence = [
    '+',
    ['*', ['sin', sunEl], ['cos', slope]],
    ['*', ['cos', sunEl], ['sin', slope], ['cos', ['-', sunAz, aspect]]]
  ];

  var variables = {vert: 1.2, sunEl: 45, sunAz: 315};

  var relief = new ol.layer.WebGLTile({
    opacity: 0.55,
    source: terrain,
    style: {
      variables: variables,
      color: ['color', ['*', 255, cosIncidence]]
    }
  });

  var map = new ol.Map({
    target: 'map',
    layers: [
      new ol.layer.Tile({source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}), opacity: 0.55}),
      relief
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.05, 40.02]),
      zoom: 9
    })
  });

  ['vert', 'sunEl', 'sunAz'].forEach(function (id) {
    var control = document.getElementById(id);
    var output = document.getElementById(id + 'Out');
    function update() {
      var value = Number(control.value);
      variables[id] = value;
      output.textContent = id === 'vert' ? String(value) : value + '°';
      relief.updateStyleVariables(variables);
    }
    update();
    control.addEventListener('input', update);
  });

})();
</script>
</body>
</html>