CanvasLayer: an example
index.html
<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Layer - CanvasLayer: an example</title>
  <style type="text/css">
    html,body{margin:0px;height:100%;width:100%}
    .container{width:100%;height:100%}
  </style>
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/maptalks.css">
  <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/[email protected]/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: 'http://{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 canvasLayer = new maptalks.CanvasLayer('c', {
        'forceRenderOnMoving' : true,
        'forceRenderOnZooming' : true
      });

      canvasLayer.prepareToDraw = function (/* context */) {
        return ['foo', 'bar'];
      };

      // param1 and param2 are prepareToDraw's return values.
      canvasLayer.draw = function (context, view, param1, param2) {
        var size = map.getSize();
        var str = param1 + ',' + param2;
        context.fillStyle = '#f00';
        context.font = 'bolder 50px sans-serif';
        var len = context.measureText(str);
        context.fillText(str, size.width / 2 - len.width / 2, size.height / 2);
        this.completeRender();
      };

      //draw when map is interacting
      canvasLayer.drawOnInteracting = function (context, view, param1, param2) {
        this.draw(context, view, param1, param2);
      };

      map.addLayer(canvasLayer);

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