Fractal

<!--
  说明：分形栅格渲染
  核心逻辑：Canvas 计算曼德博集合，toDataURL 作为 ImageStatic 源并指定 imageExtent
  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>分形栅格渲染</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:12px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar button{font:inherit;padding:4px 10px;border:1px solid #c9d0da;border-radius:5px;
              background:#fff;color:#1f2a37;cursor:pointer}
  .bar input[type=range]{width:120px}
  #info{margin-left:auto}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>迭代 <input type="range" id="iter" min="20" max="200" step="10" value="80"></label>
  <span id="iv">80</span>
  <button id="regen">重新生成</button>
  <label>透明度 <input type="range" id="op" min="20" max="100" step="5" value="85"></label>
  <span id="info">—</span>
</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').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;

  var W = 480;
  var H = 320;

  function render(maxIter) {
    var canvas = document.createElement('canvas');
    canvas.width = W;
    canvas.height = H;
    var ctx = canvas.getContext('2d');
    var img = ctx.createImageData(W, H);

    for (var py = 0; py < H; py++) {
      var ci = (py / H) * 2.4 - 1.2;
      for (var px = 0; px < W; px++) {
        var cr = (px / W) * 3.2 - 2.2;
        var zr = 0;
        var zi = 0;
        var n = 0;
        while (n < maxIter && zr * zr + zi * zi < 4) {
          var t = zr * zr - zi * zi + cr;
          zi = 2 * zr * zi + ci;
          zr = t;
          n++;
        }

        var idx = (py * W + px) * 4;
        if (n === maxIter) {
          img.data[idx] = 12;
          img.data[idx + 1] = 20;
          img.data[idx + 2] = 48;
        } else {
          var k = n / maxIter;
          img.data[idx] = Math.round(30 + 210 * k);
          img.data[idx + 1] = Math.round(120 + 100 * Math.sin(k * 3.1));
          img.data[idx + 2] = Math.round(200 - 150 * k);
        }
        img.data[idx + 3] = 255;
      }
    }

    ctx.putImageData(img, 0, 0);
    return canvas.toDataURL();
  }

  var extent = ol.proj.transformExtent([100, 28, 122, 42], 'EPSG:4326', 'EPSG:3857');

  var imageLayer = new ol.layer.Image({
    source: new ol.source.ImageStatic({
      url: render(80),
      imageExtent: extent,
      projection: 'EPSG:3857'
    }),
    opacity: 0.85
  });

  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'}) }), imageLayer],
    view: new ol.View({ center: fromLonLat([111, 35]), zoom: 4, minZoom: 2, maxZoom: 19 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var info = document.getElementById('info');

  document.getElementById('iter').addEventListener('input', function () {
    document.getElementById('iv').textContent = this.value;
  });

  document.getElementById('regen').addEventListener('click', function () {
    var iter = Number(document.getElementById('iter').value);
    var url = render(iter);
    imageLayer.setSource(new ol.source.ImageStatic({
      url: url,
      imageExtent: extent,
      projection: 'EPSG:3857'
    }));
    info.textContent = '已按 ' + iter + ' 次迭代重新生成 ' + W + '×' + H + ' 影像';
  });

  document.getElementById('op').addEventListener('input', function () {
    imageLayer.setOpacity(Number(this.value) / 100);
  });

  info.textContent = '初始影像 ' + W + '×' + H + ' · 迭代 80 次';
})();
</script>
</body>
</html>