Custom Hit Detection Renderer

<!--
  说明：自定义命中检测的中文示例，数据在页面内生成，可独立运行。
  核心逻辑：getPixelFromCoordinate 逐要素相减 + 阈值判断 + 样式切换
  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>自定义命中检测</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;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar button{font:inherit;padding:3px 9px;border:1px solid #c9ced6;background:#fff;
       border-radius:5px;cursor:pointer;color:#333}
  .bar button:hover{background:#eef2f8}
  .bar input[type=range]{width:110px;vertical-align:middle}
  .bar input[type=text]{font:inherit;padding:2px 6px;border:1px solid #c9ced6;border-radius:4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3;position:relative}
  .panel{flex:0 0 auto;max-height:34%;overflow:auto;padding:8px 12px;font-size:12px;
       background:#fff;border-top:1px solid #e3e6ea;color:#3d4451}
  .panel pre{margin:0;font-family:Consolas,"Courier New",monospace;font-size:11px;
       white-space:pre-wrap;word-break:break-all;line-height:1.5}
  .ol-attribution{font-size:11px}

</style>
</head>
<body>
<div class="bar">
<label>命中阈值 <input type="range" id="tol" min="0" max="20" value="6"></label>
<span id="info">移动鼠标到点附近</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') {
    var errBox = document.getElementById('map');
    if (errBox) {
      errBox.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;
  function rand(seed) {
    var v = Math.sin(seed * 12.9898) * 43758.5453;
    return v - Math.floor(v);
  }

  var features = [];
  for (var i = 0; i < 10; i++) {
    var lon = 116.28 + rand(i + 3) * 0.30;
    var lat = 39.82 + rand(i + 17) * 0.18;
    features.push(new ol.Feature({
      geometry: new ol.geom.Point(fromLonLat([lon, lat])),
      name: '点位 ' + (i + 1),
      active: false
    }));
  }

  var source = new ol.source.Vector({features: features});
  var layer = new ol.layer.Vector({
    source: source,
    style: function (feature) {
      var on = feature.get('active');
      return new ol.style.Style({
        image: new ol.style.Circle({
          radius: on ? 9 : 6,
          fill: new ol.style.Fill({color: on ? '#ee602a' : '#1f5fd0'}),
          stroke: new ol.style.Stroke({color: '#ffffff', width: 2})
        }),
        text: new ol.style.Text({
          text: feature.get('name'),
          offsetY: on ? -20 : -16,
          font: '500 11px sans-serif',
          fill: new ol.style.Fill({color: on ? '#8f3410' : '#3d4451'}),
          stroke: new ol.style.Stroke({color: '#ffffff', width: 3})
        })
      });
    }
  });

  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'})}), layer],
    view: new ol.View({center: fromLonLat([116.43, 39.91]), zoom: 12}),
    controls: ol.control.defaults.defaults({attribution: false, zoom: true, rotate: false})
  });

  var info = document.getElementById('info');
  var tol = document.getElementById('tol');
  var current = null;

  function hitTest(pixel) {
    var limit = 8 + (+tol.value);
    var best = null;
    var bestDist = Infinity;

    features.forEach(function (f) {
      var px = map.getPixelFromCoordinate(f.getGeometry().getCoordinates());
      if (!px) { return; }
      var d = Math.sqrt((px[0] - pixel[0]) * (px[0] - pixel[0]) +
                        (px[1] - pixel[1]) * (px[1] - pixel[1]));
      if (d < bestDist) { bestDist = d; best = f; }
    });

    return {feature: bestDist <= limit ? best : null, dist: bestDist, best: best, limit: limit};
  }

  map.on('pointermove', function (evt) {
    if (evt.dragging) { return; }
    var hit = hitTest(evt.pixel);

    if (hit.feature !== current) {
      if (current) { current.set('active', false); }
      if (hit.feature) { hit.feature.set('active', true); }
      current = hit.feature;
    }

    map.getTargetElement().style.cursor = hit.feature ? 'pointer' : '';

    if (hit.feature) {
      info.textContent = '命中 ' + hit.feature.get('name') + ' · 像素距离 ' +
        hit.dist.toFixed(1) + ' px · 阈值 ' + hit.limit.toFixed(0) + ' px';
    } else {
      info.textContent = '未命中 · 最近点 ' + (hit.best ? hit.best.get('name') : '—') +
        ' 距离 ' + hit.dist.toFixed(1) + ' px · 阈值 ' + hit.limit.toFixed(0) + ' px';
    }
  });
})();
</script>
</body>
</html>