var format = new ol.format.WKT();
  var feature = format.readFeature(
      'POLYGON((10.689697265625 -25.0927734375, 34.595947265625 ' +
          '-20.1708984375, 38.814697265625 -35.6396484375, 13.502197265625 ' +
          '-39.1552734375, 10.689697265625 -25.0927734375))');
  feature.getGeometry().transform('EPSG:4326', 'EPSG:3857');

  var vector = new ol.layer.Vector({
    source: new ol.source.Vector({
      features: [feature]
    })
  });


  var map = new ol.Map({
    layers: [raster, vector],
    target: 'map',
    controls: ol.control.defaults({
      attributionOptions: {
        collapsible: false
      }
    }),
    view: new ol.View({
      center: [0, 0],
      zoom: 2
    })
  });


  var dims = {
    a0: [1189, 841],
    a1: [841, 594],
    a2: [594, 420],
    a3: [420, 297],
    a4: [297, 210],
    a5: [210, 148]
  };

  var loading = 0;
  var loaded = 0;

  var exportButton = document.getElementById('export-pdf');

  exportButton.addEventListener('click', function() {

    exportButton.disabled = true;
    document.body.style.cursor = 'progress';

    var format = document.getElementById('format').value;
    var resolution = document.getElementById('resolution').value;
    var dim = dims[format];
    var width = Math.round(dim[0] * resolution / 25.4);
    var height = Math.round(dim[1] * resolution / 25.4);
    var size = /** @type {ol.Size} */ (map.getSize());
    var extent = map.getView().calculateExtent(size);

    var source = raster.getSource();

    var tileLoadStart = function() {
      ++loading;
    };

    var tileLoadEnd = function() {
      ++loaded;
      if (loading === loaded) {
        var canvas = this;
        window.setTimeout(function() {
          loading = 0;
          loaded = 0;
          var data = canvas.toDataURL('image/png');
          var pdf = new jsPDF('landscape', undefined, format);
          pdf.addImage(data, 'JPEG', 0, 0, dim[0], dim[1]);
          pdf.save('map.pdf');
          source.un('tileloadstart', tileLoadStart);
          source.un('tileloadend', tileLoadEnd, canvas);
          source.un('tileloaderror', tileLoadEnd, canvas);
          map.setSize(size);
          map.getView().fit(extent);
          map.renderSync();
          exportButton.disabled = false;
          document.body.style.cursor = 'auto';
        }, 100);
      }
    };

    map.once('postcompose', function(event) {
      source.on('tileloadstart', tileLoadStart);
      source.on('tileloadend', tileLoadEnd, event.context.canvas);
      source.on('tileloaderror', tileLoadEnd, event.context.canvas);
    });

    map.setSize([width, height]);
    map.getView().fit(extent);
    map.renderSync();

  }, false);
</script>