Brushing

<!--
  示例：笔刷扩展
  核心逻辑：BrushingExtension 以鼠标为中心做半径判断，圈内实例高亮、圈外变淡
  数据：页面内生成的 6000 个 POI，集中在几座城市
  依赖：deck.gl 9.0 · 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>笔刷扩展</title>
<style>
  html,body{height:100%;margin:0;background:#0d1117}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif;color:#e6e8ec}
  .bar{position:relative;z-index:5;flex:0 0 auto;padding:8px 12px;background:#161b22;border-bottom:1px solid #252c36;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#8b93a1;flex-wrap:wrap}
  .bar b{color:#58a6ff;font-weight:600}
  .bar input[type=range]{width:130px}
  #cv{flex:1 1 auto;min-height:0;width:100%}
</style>
</head>
<body>
<div class="bar">
  <span>POI <b id="n">—</b></span>
  <label>笔刷半径 <input id="r" type="range" min="20" max="260" step="10" value="110"> <b id="rv">110</b></label>
  <span>把鼠标移到图上试试</span>
</div>
<canvas id="cv"></canvas>
<script src="https://cdn.jsdelivr.net/npm/deck.gl@9.0.35/dist.min.js"></script>
<script>
(function () {
  'use strict';

  if (typeof deck === 'undefined') {
    document.body.innerHTML =
      '<div style="padding:24px;color:#ff8c74">deck.gl 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var cities = [
    [116.39, 39.90], [121.47, 31.23], [113.26, 23.12], [104.06, 30.57],
    [114.30, 30.59], [108.94, 34.34]
  ];

  var data = [];
  for (var i = 0; i < 6000; i++) {
    var c = cities[i % cities.length];
    data.push({
      lng: c[0] + (Math.random() + Math.random() - 1) * 1.9,
      lat: c[1] + (Math.random() + Math.random() - 1) * 1.4,
      kind: i % 3
    });
  }
  document.getElementById('n').textContent = data.length.toLocaleString();

  var scatter = new deck.ScatterplotLayer({
    id: 'poi',
    data: data,
    getPosition: function (d) { return [d.lng, d.lat]; },
    getRadius: 3,
    radiusUnits: 'pixels',
    radiusMinPixels: 1.5,
    getFillColor: function (d) {
      return d.kind === 0 ? [88, 166, 255, 210]
        : d.kind === 1 ? [126, 231, 135, 210]
        : [255, 190, 100, 210];
    },
    /* 开了笔刷后，圈内使用原色，圈外统一压暗 */
    extensions: [new deck.BrushingExtension()],
    brushingRadius: 110,
    brushingTarget: 'source',
    pickable: true
  });

  /* 同一扩展也能作用在文字层上，圈内圈外一起变化 */
  var labels = new deck.TextLayer({
    id: 'city-labels',
    data: cities.map(function (c, i) { return { lng: c[0], lat: c[1], name: '城市 ' + (i + 1) }; }),
    getPosition: function (d) { return [d.lng, d.lat]; },
    getText: function (d) { return d.name; },
    getSize: 13,
    getColor: [240, 245, 255],
    getPixelOffset: [0, -14],
    extensions: [new deck.BrushingExtension()],
    brushingRadius: 110,
    brushingTarget: 'source'
  });

  var deckgl = new deck.Deck({
    canvas: document.getElementById('cv'),
    width: '100%',
    height: '100%',
    initialViewState: {
      longitude: 109,
      latitude: 33,
      zoom: 3.5,
      pitch: 0,
      bearing: 0
    },
    controller: true,
    layers: [scatter, labels],
    getTooltip: function (info) {
      if (!info.object) return null;
      return info.object.name || ('POI · 类型 ' + info.object.kind);
    }
  });

  document.getElementById('r').addEventListener('input', function () {
    var v = parseInt(this.value, 10);
    document.getElementById('rv').textContent = v;
    scatter = scatter.clone({ brushingRadius: v });
    labels = labels.clone({ brushingRadius: v });
    deckgl.setProps({ layers: [scatter, labels] });
  });

  window.__deck = deckgl;
})();
</script>
</body>
</html>