Features Under Pointer

<!--
  示例：查询指针下的要素
  核心逻辑：mousemove 里 queryRenderedFeatures 按点查询，结果写入侧栏并同步高亮
  数据：页面内构造的 6 个分区多边形，部分刻意重叠
  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>查询指针下的要素</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:14px;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}
  .wrap{flex:1 1 auto;min-height:0;display:flex}
  #map{flex:1 1 auto;min-width:0}
  .side{flex:0 0 230px;border-left:1px solid #e3e6ea;background:#fff;padding:12px;overflow:auto;
        font-size:12px;color:#3a4250}
  .side h3{margin:0 0 8px;font-size:13px;color:#16181d}
  .item{padding:7px 9px;border-radius:5px;background:#f4f6f9;margin-bottom:6px}
  .item b{display:block;font-size:12.5px;color:#16181d}
  .item span{color:#77818f}
  .empty{color:#98a2b3;font-size:12px}
</style>
</head>
<body>
<div class="bar">
  <span>分区 <b>6</b></span>
  <span>指针下 <b id="n">0</b> 个</span>
  <span>重叠处会同时返回多个要素</span>
</div>
<div class="wrap">
  <div id="map"></div>
  <div class="side">
    <h3>指针下的要素</h3>
    <div id="list"><div class="empty">把指针移到色块上</div></div>
  </div>
</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;
  }

  function block(lng, lat, w, h) {
    return [[
      [lng - w, lat - h], [lng + w, lat - h],
      [lng + w, lat + h], [lng - w, lat + h],
      [lng - w, lat - h]
    ]];
  }

  var zones = [
    { id: 1, name: '华北片区', q: [116, 39, 5, 3.4] },
    { id: 2, name: '华东片区', q: [120, 32, 5.5, 3.2] },
    { id: 3, name: '华南片区', q: [113, 24, 4.5, 2.8] },
    { id: 4, name: '西南片区', q: [104, 29, 6, 3.6] },
    { id: 5, name: '重叠片区 A', q: [109, 34, 4, 2.6] },
    { id: 6, name: '重叠片区 B', q: [111, 35, 4, 2.6] }
  ];

  var geojson = {
    type: 'FeatureCollection',
    features: zones.map(function (z) {
      return {
        type: 'Feature',
        properties: { id: z.id, name: z.name },
        geometry: { type: 'Polygon', coordinates: block.apply(null, z.q) }
      };
    })
  };

  var map = new maplibregl.Map({
    container: 'map',
    style: 'https://demotiles.maplibre.org/style.json',
    center: [110, 33],
    zoom: 3.4,
    attributionControl: { compact: true, customAttribution: 'MapLibre demo tiles' }
  });

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

  var listEl = document.getElementById('list');
  var nEl = document.getElementById('n');

  map.on('load', function () {
    map.addSource('zones', {
      type: 'geojson',
      data: geojson,
      promoteId: 'id'
    });

    map.addLayer({
      id: 'zones',
      type: 'fill',
      source: 'zones',
      paint: {
        'fill-color': [
          'case',
          ['boolean', ['feature-state', 'hover'], false],
          '#ff922b',
          '#4dabf7'
        ],
        'fill-opacity': 0.35
      }
    });

    map.addLayer({
      id: 'zones-line',
      type: 'line',
      source: 'zones',
      paint: {
        'line-color': '#1c4e80',
        'line-width': 1
      }
    });
  });

  var hovered = null;

  function render(features) {
    nEl.textContent = features.length;
    if (!features.length) {
      listEl.innerHTML = '<div class="empty">把指针移到色块上</div>';
      return;
    }
    listEl.innerHTML = features.map(function (f) {
      return '<div class="item"><b>' + f.properties.name + '</b>' +
        '<span>要素 id ' + f.properties.id + '</span></div>';
    }).join('');
  }

  map.on('mousemove', function (e) {
    if (!map.getLayer('zones')) return;

    var hit = map.queryRenderedFeatures(e.point, { layers: ['zones'] });

    var next = hit.length ? hit[0].properties.id : null;
    if (next !== hovered) {
      if (hovered !== null) {
        map.setFeatureState({ source: 'zones', id: hovered }, { hover: false });
      }
      hovered = next;
      if (hovered !== null) {
        map.setFeatureState({ source: 'zones', id: hovered }, { hover: true });
      }
    }

    map.getCanvas().style.cursor = hit.length ? 'pointer' : '';
    render(hit);
  });

  map.on('mouseout', function () {
    if (hovered !== null) {
      map.setFeatureState({ source: 'zones', id: hovered }, { hover: false });
      hovered = null;
    }
    render([]);
  });

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