用鼠标设置图层遮罩
index.html
<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>图层 - 用鼠标设置图层遮罩</title>
  <style type="text/css">
    html,body{margin:0px;height:100%;width:100%}
    .container{width:100%;height:100%}
  </style>
  <link rel="stylesheet" href="https://unpkg.com/maptalks/dist/maptalks.css">
  <script type="text/javascript" src="https://unpkg.com/maptalks/dist/maptalks.min.js"></script>
  <body>
    <div id="map" class="container"></div>

    <script>
      var map = new maptalks.Map('map', {
        center: [-0.113049,51.498568],
        zoom: 14,
        baseLayer: new maptalks.TileLayer('base', {
          urlTemplate: 'https://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png',
          subdomains: ['a','b','c','d'],
          attribution: '&copy; <a href="http://osm.org">OpenStreetMap</a> contributors, &copy; <a href="https://carto.com/">CARTO</a>'
        })
      });

      var layer = new maptalks.VectorLayer('vector')
          .addTo(map);

      map.on('mousemove', function (e) {
        if (!layer.getMask()) {
          layer.setMask(new maptalks.Marker(e.coordinate, {
            'symbol': {
              'markerType': 'ellipse',
              'markerWidth': 200,
              'markerHeight': 200
            }
          }));
        } else {
          layer.getMask().setCoordinates(e.coordinate);
        }
      });

      var extent = map.getExtent(),
        min = extent.getMin(),
        w = extent.getWidth(),
        h = extent.getHeight(),
        markers = [];
      for (var i = 0; i < 100; i++) {
        markers.push(new maptalks.Marker([min.x + Math.random() * w, min.y + Math.random() * h]));
      }
      layer.addGeometry(markers);

    </script>
  </body>
</html>
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