gistfile1.txt

// dynamic sprite
$sprite: sprite-map("sprite/*.png", $spacing: 5);
$sprite-retina: sprite-map("sprite-retina/*.png", $spacing: 30);
$sprite-background: sprite-url($sprite) no-repeat transparent;
$sprite-retina-background-image: sprite-url($sprite-retina);

@mixin background-sprite($selector, $setHeight: false, $setWidth: false, $offset-x: 0, $offset-y: 0, $retina-offset-x: false, $retina-offset-y: false) {
  background: $sprite-background;
  background-position: sprite-position($sprite, $selector, $offset-x, $offset-y);
  background-repeat: no-repeat;
  @if $setHeight {
    height: image-height(sprite-file($sprite, $selector));
  }
  text-shadow: none;
  @if $setWidth {
    width: image-width(sprite-file($sprite, $selector));
  }
  //retina
  @media (-webkit-min-device-pixel-ratio: 2), (-o-min-device-pixel-ratio: 3/2), (min-device-pixel-ratio: 2) {
    @if (sprite-position($sprite, $selector) != sprite-position($sprite-retina, $selector)) {
      @if ($retina-offset-x) {
        $offset-x: $retina-offset-x;
      }
       @if ($retina-offset-y) {
        $offset-y: $retina-offset-y;
      }
      $ypos: round(nth(sprite-position($sprite-retina, $selector, $offset-x, $offset-y), 2) / 2);
      background-position: 0 $ypos;
    }
    background-size: (ceil(image-width(sprite-path($sprite))), auto);
    background-image: $sprite-retina-background-image;
  }
}