index.html
<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Map - Map&#x27;s magnifier</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>
      // This work is submitted by @1dent1ty https://github.com/1dent1ty
      // Inspired by openlayers https://openlayers.org/en/latest/examples/magnify.html

      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 mousePosition = null;

      map.on('mousemove', function (e) {
        mousePosition = e.containerPoint;
        map.getRenderer().setToRedraw();
      });

      map.on('mouseout', function () {
        mousePosition = null;
        map.getRenderer().setToRedraw();
      });

      map.on('renderend', function (e) {
        if (!mousePosition) {
          return;
        }
        // map's canvas context
        var ctx = e.context;
        // radius of magnifier
        var radius = 150;
        var pixelRatio = (window.devicePixelRatio || (window.screen.deviceXDPI / window.screen.logicalXDPI));
        radius *= (pixelRatio > 1 ? 2 : 1);
        var centerX = mousePosition.x * pixelRatio,
          centerY = mousePosition.y * pixelRatio;
        var originX = centerX - radius,
          originY = centerY - radius;
        var size = 2 * radius + 2;
        // manipulate pixel values to magnify
        var sourceData = ctx.getImageData(originX, originY, size, size).data;
        var dest = ctx.createImageData(size, size);
        var destData = dest.data;
        for (var j = 0; j < size; ++j) {
          for (var i = 0; i < size; ++i) {
            var dI = i - radius;
            var dJ = j - radius;
            var dist = Math.sqrt(dI * dI + dJ * dJ);
            var sourceI = i;
            var sourceJ = j;
            if (dist < radius) {
              sourceI = Math.round(radius + dI / 2);
              sourceJ = Math.round(radius + dJ / 2);
            }
            var destOffset = (j * size + i) * 4;
            var sourceOffset = (sourceJ * size + sourceI) * 4;
            destData[destOffset] = sourceData[sourceOffset];
            destData[destOffset + 1] = sourceData[sourceOffset + 1];
            destData[destOffset + 2] = sourceData[sourceOffset + 2];
            destData[destOffset + 3] = sourceData[sourceOffset + 3];
          }
        }
        // draw magnifier's outline
        ctx.beginPath();
        ctx.strokeStyle = '#bbb';
        ctx.lineWidth = 2;
        ctx.arc(centerX, centerY, radius + 2, 0, 2 * Math.PI);
        ctx.stroke();
        ctx.closePath();

        // draw magnified image and clip it by circle
        ctx.drawImage(createMagCircle(dest, size), centerX - size / 2, centerY - size / 2);
      });

      //draw image data into a canvas, and clip it by a circle with diameter of size
      function createMagCircle(imageData, size) {
        var magImg = document.createElement('canvas');
        var magCircle = document.createElement('canvas');

        magImg.width = magImg.height = magCircle.width = magCircle.height = size;
        magImg.getContext('2d').putImageData(imageData, 0, 0);

        var ctx = magCircle.getContext('2d');
        ctx.beginPath();
        ctx.arc(size / 2, size / 2, size / 2, 0, 2 * Math.PI);
        // clip canvas
        ctx.clip();
        ctx.drawImage(magImg, 0, 0);
        return magCircle;
      }

    </script>
  </body>
</html>
Copied!