// Get device pixel ratio
function getDPR() {
  var mediaQuery;
  // Fix fake window.devicePixelRatio on mobile Firefox
  var is_firefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1;
  if (window.devicePixelRatio !== undefined && !is_firefox) {
    return window.devicePixelRatio;
  } else if (window.matchMedia) {
      mediaQuery = "(-webkit-min-device-pixel-ratio: 1.5),\
            (min--moz-device-pixel-ratio: 1.5),\
            (-o-min-device-pixel-ratio: 3/2),\
            (min-resolution: 1.5dppx)";
    if (window.matchMedia(mediaQuery).matches)
      return 1.5;
      mediaQuery = "(-webkit-min-device-pixel-ratio: 2),\
            (min--moz-device-pixel-ratio: 2),\
            (-o-min-device-pixel-ratio: 2/1),\
            (min-resolution: 2dppx)";
    if (window.matchMedia(mediaQuery).matches)
      return 2;
      mediaQuery = "(-webkit-min-device-pixel-ratio: 0.75),\
            (min--moz-device-pixel-ratio: 0.75),\
            (-o-min-device-pixel-ratio: 3/4),\
            (min-resolution: 0.75dppx)";
    if (window.matchMedia(mediaQuery).matches)
      return 0.7;
  } else
    return 1;
}