Shaded Relief

<!--
  示例：地形晕渲
  要点：由高程场算坡度坡向再上晕渲色，光源方位可调
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
  替代：官方读真实 DEM 瓦片，这里用页面内生成的高程函数算同构晕渲
-->
<!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>地形晕渲</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;color:#16181d}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:16px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  .bar input{width:110px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span>光源方位 <b id="az">315</b>°</span>
  <input type="range" id="azR" min="0" max="360" value="315" step="15">
  <span>光源高度 <b id="al">45</b>°</span>
  <input type="range" id="alR" min="5" max="85" value="45" step="5">
  <span>晕渲不透明度 <b id="op">80</b>%</span>
  <input type="range" id="opR" min="0" max="100" value="80" step="5">
</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 (!window.ol) {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查 cdn.jsdelivr.net 是否可访问';
    return;
  }

  var R = 6378137;
  var DEG = 180 / Math.PI;
  var az = 315 * Math.PI / 180;
  var alt = 45 * Math.PI / 180;

  function elev(lon, lat) {
    return 900 + 700 * Math.sin(lon * 1.6) * Math.cos(lat * 1.9)
         + 300 * Math.sin(lon * 4.3 + 0.7) * Math.cos(lat * 3.7)
         + 120 * Math.sin(lon * 9.1) * Math.cos(lat * 8.3);
  }

  var canvasFunction = function (extent, resolution, pixelRatio, size) {
    var w = Math.max(1, Math.round(size[0]));
    var h = Math.max(1, Math.round(size[1]));
    var canvas = document.createElement('canvas');
    canvas.width = w;
    canvas.height = h;
    var ctx = canvas.getContext('2d');
    var img = ctx.createImageData(w, h);
    var sx = (extent[2] - extent[0]) / w;
    var sy = (extent[3] - extent[1]) / h;
    var light = [Math.cos(alt) * Math.sin(az), Math.cos(alt) * Math.cos(az), Math.sin(alt)];

    for (var y = 0; y < h; y++) {
      var my = extent[3] - (y + 0.5) * sy;
      var lat = (2 * Math.atan(Math.exp(my / R)) - Math.PI / 2) * DEG;
      for (var x = 0; x < w; x++) {
        var lon = (extent[0] + (x + 0.5) * sx) / R * DEG;
        var dLon = 0.002, dLat = 0.002;
        var gx = (elev(lon + dLon, lat) - elev(lon - dLon, lat)) / (2 * dLon * 111000);
        var gy = (elev(lon, lat + dLat) - elev(lon, lat - dLat)) / (2 * dLat * 111000);
        var nx = -gx, ny = -gy, nz = 1;
        var len = Math.sqrt(nx * nx + ny * ny + nz * nz);
        var shade = (nx / len * light[0] + ny / len * light[1] + nz / len * light[2]);
        shade = Math.max(0.08, shade);
        var v = 60 + shade * 190;
        var i = (y * w + x) * 4;
        img.data[i] = v * 1.05;
        img.data[i + 1] = v;
        img.data[i + 2] = v * 0.9;
        img.data[i + 3] = 225;
      }
    }
    ctx.putImageData(img, 0, 0);
    return canvas;
  };

  var source = new ol.source.ImageCanvas({ canvasFunction: canvasFunction });
  var relief = new ol.layer.Image({ source: source, opacity: 0.8 });

  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'}) }), relief],
    view: new ol.View({ center: ol.proj.fromLonLat([100.5, 30.0]), zoom: 6 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  function bind(id, out, fn) {
    document.getElementById(id).addEventListener('input', function () {
      document.getElementById(out).textContent = this.value;
      fn(Number(this.value));
    });
  }

  bind('azR', 'az', function (v) { az = v * Math.PI / 180; source.changed(); });
  bind('alR', 'al', function (v) { alt = v * Math.PI / 180; source.changed(); });
  bind('opR', 'op', function (v) { relief.setOpacity(v / 100); });
})();
</script>
</body>
</html>