Mask

<!--
  示例：遮罩扩展
  核心逻辑：MaskExtension 用一个面图层当模板，目标图层的像素只在模板内保留
  数据：页面内生成的正六边形遮罩与 8000 个随机点
  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>遮罩扩展</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 label{display:flex;gap:5px;align-items:center;cursor:pointer}
  #cv{flex:1 1 auto;min-height:0;width:100%}
</style>
</head>
<body>
<div class="bar">
  <span>遮罩点 <b id="n">—</b></span>
  <label><input id="inv" type="checkbox"> 反转遮罩</label>
  <label><input id="show" type="checkbox" checked> 显示遮罩轮廓</label>
  <span>只有模板范围内的像素被画出来</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;
  }

  /* maskId 必须等于遮罩层的 id */
  var MASK_ID = 'mask-source';

  /* 用六边形当遮罩模板，边界比矩形更有说服力 */
  function hexagon(lng, lat, r) {
    var pts = [];
    for (var i = 0; i < 6; i++) {
      var a = Math.PI / 180 * (60 * i - 30);
      pts.push([lng + Math.cos(a) * r, lat + Math.sin(a) * r * 0.82]);
    }
    pts.push(pts[0]);
    return pts;
  }

  var maskPolygon = hexagon(112, 32, 9);

  var points = [];
  for (var i = 0; i < 8000; i++) {
    points.push({
      lng: 96 + Math.random() * 32,
      lat: 20 + Math.random() * 24,
      v: Math.random()
    });
  }
  document.getElementById('n').textContent = points.length.toLocaleString();

  /* 遮罩层只声明 operation，本身不参与正常绘制，只写模板缓冲 */
  var maskLayer = new deck.SolidPolygonLayer({
    id: 'mask-source',
    data: [{ polygon: maskPolygon }],
    getPolygon: function (d) { return d.polygon; },
    filled: true,
    stroked: false,
    getFillColor: [255, 255, 255, 255],
    operation: 'mask'
  });

  var targetLayer = new deck.ScatterplotLayer({
    id: 'masked-points',
    data: points,
    getPosition: function (d) { return [d.lng, d.lat]; },
    getRadius: 2,
    radiusUnits: 'pixels',
    radiusMinPixels: 1,
    getFillColor: function (d) {
      return [Math.round(90 + 150 * d.v), Math.round(200 - 90 * d.v), 255, 210];
    },
    extensions: [new deck.MaskExtension()],
    maskId: MASK_ID,
    maskInverted: false
  });

  /* 轮廓层不开遮罩，否则它自己也会被裁掉 */
  var outlineLayer = new deck.PathLayer({
    id: 'mask-outline',
    data: [{ path: maskPolygon }],
    getPath: function (d) { return d.path; },
    getColor: [255, 190, 90, 230],
    getWidth: 2,
    widthUnits: 'pixels'
  });

  var deckgl = new deck.Deck({
    canvas: document.getElementById('cv'),
    width: '100%',
    height: '100%',
    initialViewState: {
      longitude: 112,
      latitude: 32,
      zoom: 3.6,
      pitch: 0,
      bearing: 0
    },
    controller: true,
    layers: [maskLayer, targetLayer, outlineLayer]
  });

  document.getElementById('inv').addEventListener('change', function () {
    targetLayer.setProps({ maskInverted: this.checked });
  });

  document.getElementById('show').addEventListener('change', function () {
    outlineLayer.setProps({ visible: this.checked });
  });

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