Performance

<!--
  示例：性能优化
  核心逻辑：8000 点同数据分别走 heatmap 与 circle，实时 FPS 表 + setData 耗时对比
  依赖：MapLibre GL JS 4 · jsDelivr CDN · demotiles 样式
-->
<!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>性能优化</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.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;display:flex;gap:12px;align-items:center;padding:8px 12px;
       background:#f6f7f9;border-bottom:1px solid #e3e6ea;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  .bar select{font:12px/1.5 inherit;padding:2px 6px}
  .btn{border:1px solid #cdd3db;background:#fff;border-radius:4px;padding:3px 9px;
       font:12px/1.5 inherit;color:#16181d;cursor:pointer}
  #map{flex:1 1 auto;min-height:0}
</style>
</head>
<body>
<div class="bar">
  <label>渲染方式
    <select id="mode">
      <option value="heat">heatmap</option>
      <option value="circle">circle × 8000</option>
    </select>
  </label>
  <button class="btn" id="rebuild">重建数据</button>
  <span>FPS <b id="fps">—</b></span>
  <span>点数 <b>8000</b></span>
  <span>setData <b id="ms">—</b></span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/maplibre-gl@4/dist/maplibre-gl.js"></script>
<script>
(function () {
  'use strict';

  if (typeof maplibregl === 'undefined') {
    document.body.innerHTML =
      '<div style="padding:24px;color:#b42318">MapLibre 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var N = 8000;

  function build(n) {
    var features = new Array(n);
    for (var i = 0; i < n; i++) {
      features[i] = {
        type: 'Feature',
        properties: { v: Math.random() },
        geometry: {
          type: 'Point',
          coordinates: [
            100 + Math.random() * 22,
            27 + Math.random() * 16
          ]
        }
      };
    }
    return { type: 'FeatureCollection', features: features };
  }

  var map = new maplibregl.Map({
    container: 'map',
    style: 'https://demotiles.maplibre.org/style.json',
    center: [111, 34],
    zoom: 3.6,
    attributionControl: { compact: true, customAttribution: 'MapLibre demo tiles' }
  });

  map.addControl(new maplibregl.NavigationControl(), 'top-right');

  function setMode(mode) {
    if (!map.getLayer('heat') || !map.getLayer('dots')) return;
    map.setLayoutProperty('heat', 'visibility', mode === 'heat' ? 'visible' : 'none');
    map.setLayoutProperty('dots', 'visibility', mode === 'circle' ? 'visible' : 'none');
  }

  map.on('load', function () {
    map.addSource('pts', { type: 'geojson', data: build(N) });

    map.addLayer({
      id: 'heat',
      type: 'heatmap',
      source: 'pts',
      paint: {
        'heatmap-radius': ['interpolate', ['linear'], ['zoom'], 2, 12, 6, 26],
        'heatmap-intensity': 0.9,
        'heatmap-opacity': 0.75
      }
    });

    map.addLayer({
      id: 'dots',
      type: 'circle',
      source: 'pts',
      layout: { visibility: 'none' },
      paint: {
        'circle-radius': 2,
        'circle-color': '#1f5fd0',
        'circle-opacity': 0.65
      }
    });
  });

  document.getElementById('mode').addEventListener('change', function () {
    setMode(this.value);
  });

  document.getElementById('rebuild').addEventListener('click', function () {
    var src = map.getSource('pts');
    if (!src) return;
    var t0 = performance.now();
    src.setData(build(N));
    var t1 = performance.now();
    document.getElementById('ms').textContent = (t1 - t0).toFixed(1) + ' ms';
  });

  var frames = 0;
  var mark = performance.now();

  function loop(ts) {
    frames++;
    if (ts - mark >= 1000) {
      document.getElementById('fps').textContent = frames;
      frames = 0;
      mark = ts;
    }
    requestAnimationFrame(loop);
  }
  requestAnimationFrame(loop);

  map.on('error', function (e) {
    if (e.error) console.warn('地图错误：' + e.error.message);
  });
})();
</script>
</body>
</html>