goog.require('ol.Map');
goog.require('ol.View2D');
goog.require('ol.layer.Tile');
goog.require('ol.source.OSM');

var osm = new ol.layer.Tile({
  source: new ol.source.OSM()
});

var map = new ol.Map({
  layers: [osm],
  renderer: 'canvas',
  target: 'map',
  view: new ol.View2D({
    center: [0, 0],
    zoom: 2
  })
});

osm.on('precompose', function(event) {
  var ctx = event.context;
  ctx.save();
  ctx.translate(ctx.canvas.width / 2, ctx.canvas.height / 2);
  ctx.scale(3, 3);
  ctx.translate(-75, -80);
  ctx.beginPath();
  ctx.moveTo(75, 40);
  ctx.bezierCurveTo(75, 37, 70, 25, 50, 25);
  ctx.bezierCurveTo(20, 25, 20, 62.5, 20, 62.5);
  ctx.bezierCurveTo(20, 80, 40, 102, 75, 120);
  ctx.bezierCurveTo(110, 102, 130, 80, 130, 62.5);
  ctx.bezierCurveTo(130, 62.5, 130, 25, 100, 25);
  ctx.bezierCurveTo(85, 25, 75, 37, 75, 40);
  ctx.clip();
  ctx.setTransform(1, 0, 0, 1, 0, 0);
});

osm.on('postcompose', function(event) {
  var ctx = event.context;
  ctx.restore();
});