Label Declutter

<!--
  示例：标注避让
  要点：ol.style.Style 的 declutter 开关控制文字碰撞检测，切换时重建样式
  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>标注避让</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}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="declutter" checked> 标注避让</label>
  <span>放大后可看到更多被释放的标注</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 features = [];

  /* 6×7 网格点位，间距很小，必然产生文字压盖 */
  for (var row = 0; row < 6; row++) {
    for (var col = 0; col < 7; col++) {
      features.push(new ol.Feature({
        geometry: new ol.geom.Point(fromLonLat([
          116.376 + col * 0.0045,
          39.900 + row * 0.0038
        ])),
        name: 'P' + row + col
      }));
    }
  }

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

  function buildStyle(useDeclutter) {
    return function (feature) {
      return new ol.style.Style({
        declutter: useDeclutter,
        image: new ol.style.Circle({
          radius: 4,
          fill: new ol.style.Fill({ color: '#1f5fd0' }),
          stroke: new ol.style.Stroke({ color: '#ffffff', width: 1 })
        }),
        text: new ol.style.Text({
          text: feature.get('name'),
          font: '600 12px sans-serif',
          offsetY: -10,
          fill: new ol.style.Fill({ color: '#16181d' }),
          stroke: new ol.style.Stroke({ color: '#ffffff', width: 3 })
        })
      });
    };
  }

  layer.setStyle(buildStyle(true));

  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'}) }), layer],
    view: new ol.View({
      center: fromLonLat([116.3915, 39.9095]),
      zoom: 14
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  document.getElementById('declutter').addEventListener('change', function () {
    layer.setStyle(buildStyle(this.checked));
  });
})();
</script>
</body>
</html>