Icon Sprite Webgl

<!--
  示例：精灵图标 — OpenLayers icon-sprite-webgl
  核心逻辑：Canvas 画一张精灵贴图，Icon 用 offset/size 取子图，三千个点共用这份贴图
  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>精灵图标</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}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span>三种符号共用一张 96 × 32 精灵图</span>
  <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;
  }

  /* 一张贴图横向排三个 32 × 32 符号 */
  function makeSprite() {
    var c = document.createElement('canvas');
    c.width = 96;
    c.height = 32;
    var ctx = c.getContext('2d');

    function badge(ox, color, glyph) {
      ctx.beginPath();
      ctx.arc(ox + 16, 16, 13, 0, Math.PI * 2);
      ctx.fillStyle = color;
      ctx.fill();
      ctx.lineWidth = 3;
      ctx.strokeStyle = '#ffffff';
      ctx.stroke();

      ctx.fillStyle = '#ffffff';
      ctx.font = '600 15px sans-serif';
      ctx.textAlign = 'center';
      ctx.textBaseline = 'middle';
      ctx.fillText(glyph, ox + 16, 17);
    }

    badge(0, '#1f5fd0', 'A');
    badge(32, '#2f9e44', 'B');
    badge(64, '#e8590c', 'C');
    return c.toDataURL();
  }

  var sprite = makeSprite();
  var scale = 0.85;

  function iconFor(index) {
    return new ol.style.Icon({
      src: sprite,
      /* 起点 + 尺寸决定取哪一格 */
      offset: [index * 32, 0],
      size: [32, 32],
      scale: scale,
      anchor: [0.5, 0.5],
      anchorXUnits: 'fraction',
      anchorYUnits: 'fraction'
    });
  }

  var icons = [iconFor(0), iconFor(1), iconFor(2)];

  var features = [];
  var COUNT = 3000;

  for (var i = 0; i < COUNT; i++) {
    var lon = 116.25 + Math.random() * 0.28;
    var lat = 39.82 + Math.random() * 0.18;
    features.push(new ol.Feature({
      geometry: new ol.geom.Point(ol.proj.fromLonLat([lon, lat])),
      kind: i % 3
    }));
  }

  var source = new ol.source.Vector({ features: features });

  var layer = new ol.layer.Vector({
    source: source,
    style: function (feature) {
      return new ol.style.Style({ image: icons[feature.get('kind')] });
    },
    /* 大量点降低重绘频率，避免每次交互都重建样式 */
    updateWhileAnimating: false,
    updateWhileInteracting: false
  });

  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: 0.75 }),
      layer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.39, 39.91]),
      zoom: 12,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  document.getElementById('info').textContent =
    '点要素 ' + COUNT + ' · 精灵图 ' + sprite.length + ' 字符（data URL）';
})();
</script>
</body>
</html>