maptalks - Custom processing of tile images

Custom processing of tile images

index.html

<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>TileLayer and Geo-Projections - Custom processing of tile images</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 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>'
      });

      //generate tile url
      baseLayer.getTileUrl = function (x, y, z) {
        //replace with your own
        //e.g. return a url pointing to your sqlite database
        return maptalks.TileLayer.prototype.getTileUrl.call(this, x, y, z);
      };

      baseLayer.on('renderercreate', function (e) {
        //load tile image
        //   img(Image): an Image object
        //   url(String): the url of the tile
        e.renderer.loadTileImage = function (img, url) {
          //mocking getting image's base64
          //replace it by your own, e.g. load from sqlite database
          var remoteImage = new Image();
          remoteImage.crossOrigin = 'anonymous';
          remoteImage.onload = function () {
            var base64 = getBase64Image(remoteImage);
            img.src = base64;
          };
          remoteImage.src = url;
        };
      });

      var canvas;

      function getCanvas() {
        if (canvas) {
          return canvas;
        }
        canvas = document.createElement('canvas');
        return canvas;
      }

      function getBase64Image(img) {
        var canvas = getCanvas();
        canvas.width = img.width;
        canvas.height = img.height;

        var ctx = canvas.getContext('2d');
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        ctx.drawImage(img, 0, 0);

        ctx.save();
        ctx.filter = 'sepia(100%) invert(90%)';
        ctx.drawImage(img, 0, 0);
        ctx.restore();
        ctx.fillStyle = 'white';
        ctx.font = '20px serif';
        ctx.textAlign = 'center';
        ctx.fillText('hello maptalks', canvas.width / 2, canvas.height / 2);

        ctx.strokeStyle = 'white';
        ctx.lineWidth = 0.1;
        ctx.rect(0, 0, canvas.width, canvas.height);
        ctx.stroke();

        var dataURL = canvas.toDataURL('image/jpg', 0.7);
        return dataURL;
      }

      var map = new maptalks.Map('map', {
        center: [-0.113049, 51.498568],
        zoom: 11,
        baseLayer: baseLayer
      });



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

var baseLayer = new maptalks.TileLayer('base', {
  urlTemplate: 'https://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png',
  subdomains: ["a", "b", "c", "d"],
  attribution: '© <a href="http://osm.org">OpenStreetMap</a>  contributors, © <a href="https://carto.com/">CARTO</a> '
});

//generate tile url
baseLayer.getTileUrl = function(x, y, z) {
  //replace with your own
  //e.g. return a url pointing to your sqlite database
  return maptalks.TileLayer.prototype.getTileUrl.call(this, x, y, z);
};

baseLayer.on('renderercreate', function(e) {
  //load tile image
  //   img(Image): an Image object
  //   url(String): the url of the tile
  e.renderer.loadTileImage = function(img, url) {
    //mocking getting image's base64
    //replace it by your own, e.g. load from sqlite database
    var remoteImage = new Image();
    remoteImage.crossOrigin = 'anonymous';
    remoteImage.onload = function() {
      var base64 = getBase64Image(remoteImage);
      img.src = base64;
    };
    remoteImage.src = url;
  };
});

var canvas;

function getCanvas() {
  if (canvas) {
    return canvas;
  }
  canvas = document.createElement('canvas');
  return canvas;
}

function getBase64Image(img) {
  var canvas = getCanvas();
  canvas.width = img.width;
  canvas.height = img.height;

var ctx = canvas.getContext('2d');
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.drawImage(img, 0, 0);

ctx.save();
  ctx.filter = 'sepia(100%) invert(90%)';
  ctx.drawImage(img, 0, 0);
  ctx.restore();
  ctx.fillStyle = 'white';
  ctx.font = '20px serif';
  ctx.textAlign = 'center';
  ctx.fillText('hello maptalks', canvas.width / 2, canvas.height / 2);

ctx.strokeStyle = 'white';
  ctx.lineWidth = 0.1;
  ctx.rect(0, 0, canvas.width, canvas.height);
  ctx.stroke();

var dataURL = canvas.toDataURL('image/jpg', 0.7);
  return dataURL;
}

var map = new maptalks.Map('map', {
  center: [-0.113049, 51.498568],
  zoom: 11,
  baseLayer: baseLayer
});