Layer Swipe example

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<!DOCTYPE html>
<html>
<head>
<title>Layer Swipe example</title>
<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="http://openlayers.org/en/v3.9.0/css/ol.css" type="text/css">
<script src="http://openlayers.org/en/v3.9.0/build/ol.js"></script>

</head>
<body>
<div class="container-fluid">

<div class="row-fluid">
  <div class="span12">
    <div id="map" class="map"></div>
    <input id="swipe" type="range" style="width: 100%">
  </div>
</div>

</div>
<script>
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',
    imagerySet: 'Aerial'
  })
});

var map = new ol.Map({
  layers: [osm, bing],
  target: 'map',
  controls: ol.control.defaults({
    attributionOptions: /** @type {olx.control.AttributionOptions} */ ({
      collapsible: false
    })
  }),
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

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

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

swipe.addEventListener('input', function() {
  map.render();
}, false);

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