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

var osm = new ol.layer.Tile({
  source: new ol.source.OSM()
});
var bing = new ol.layer.Tile({
  source: new ol.source.BingMaps({
    key: 'Ak-dzM4wZjSqTlzveKz5u0d4IQ4bRzVI309GxmkgSVr1ewS6iPSrOvOKhA-CJlm3',
    style: 'Aerial'
  })
});

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

var swipe = document.getElementById('swipe');

bing.on('precompose', function(event) {
  var ctx = event.getContext();
  var width = ctx.canvas.width * (swipe.value / 100);

  ctx.save();
  ctx.beginPath();
  ctx.rect(width, 0, ctx.canvas.width - width, ctx.canvas.height);
  ctx.clip();
});

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

swipe.addEventListener('change', function() {
  map.requestRenderFrame();
}, false);