Earthquake Custom Symbol

<!--
  说明：自定义地震符号
  核心逻辑：Canvas 绘制同心圆与十字线，toDataURL 作为 Icon 源并按震级缓存
  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>自定义地震符号</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;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}
  #info{margin-left:auto}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button id="tone">切换底图色调</button>
  <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 quakes = [
    [103.40, 31.00, 6.1, '汶川'], [102.98, 30.30, 5.6, '芦山'],
    [103.90, 33.20, 5.2, '九寨沟'], [97.00, 33.10, 4.8, '玉树'],
    [103.30, 27.10, 4.3, '鲁甸'], [101.90, 30.00, 3.9, '康定'],
    [104.60, 29.60, 4.6, '自贡'], [100.20, 26.90, 5.0, '丽江']
  ];

  function makeSymbol(color, radius) {
    var size = radius * 2 + 14;
    var canvas = document.createElement('canvas');
    canvas.width = size;
    canvas.height = size;
    var ctx = canvas.getContext('2d');
    var c = size / 2;

    ctx.strokeStyle = color;
    ctx.lineWidth = 2;
    ctx.beginPath();
    ctx.arc(c, c, radius, 0, Math.PI * 2);
    ctx.stroke();

    ctx.globalAlpha = 0.6;
    ctx.beginPath();
    ctx.arc(c, c, radius * 0.55, 0, Math.PI * 2);
    ctx.stroke();
    ctx.globalAlpha = 1;

    ctx.beginPath();
    ctx.moveTo(c, 4);
    ctx.lineTo(c, size - 4);
    ctx.moveTo(4, c);
    ctx.lineTo(size - 4, c);
    ctx.stroke();

    ctx.fillStyle = color;
    ctx.beginPath();
    ctx.arc(c, c, 2.5, 0, Math.PI * 2);
    ctx.fill();

    return canvas.toDataURL();
  }

  var cache = {};

  function styleFn(feature) {
    var mag = feature.get('mag');
    var bucket = mag >= 5.5 ? 'high' : mag >= 4.5 ? 'mid' : 'low';
    if (!cache[bucket]) {
      cache[bucket] = makeSymbol(
        bucket === 'high' ? '#c8281c' : bucket === 'mid' ? '#e06a3b' : '#1f5fd0',
        bucket === 'high' ? 15 : bucket === 'mid' ? 11 : 8
      );
    }
    return new ol.style.Style({
      image: new ol.style.Icon({
        src: cache[bucket],
        anchor: [0.5, 0.5]
      }),
      text: new ol.style.Text({
        text: feature.get('name') + ' ' + mag,
        font: '600 11px sans-serif',
        offsetY: 26,
        fill: new ol.style.Fill({ color: '#16181d' }),
        stroke: new ol.style.Stroke({ color: '#ffffff', width: 3 })
      })
    });
  }

  var features = quakes.map(function (q) {
    var f = new ol.Feature({ geometry: new ol.geom.Point(fromLonLat([q[0], q[1]])) });
    f.set('mag', q[2]);
    f.set('name', q[3]);
    return f;
  });

  var layer = new ol.layer.Vector({
    source: new ol.source.Vector({ features: features }),
    style: styleFn
  });

  var osmLayer = 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: 1
  });

  var map = new ol.Map({
    target: 'map',
    layers: [osmLayer, layer],
    view: new ol.View({ center: fromLonLat([102, 30.5]), zoom: 6, minZoom: 2, maxZoom: 19 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var dark = false;
  document.getElementById('tone').addEventListener('click', function () {
    dark = !dark;
    osmLayer.setOpacity(dark ? 0.45 : 1);
    document.getElementById('info').textContent = dark ? '底图已被压暗，符号仍清晰' : '底图恢复原始亮度';
  });

  document.getElementById('info').textContent = '共 ' + features.length + ' 个震中';
})();
</script>
</body>
</html>