Using Compass to generate normal and retina sprite maps

compass-retina-sprites.scss

$sprites: sprite-map("sprites/*.png");
$sprites-retina: sprite-map("sprites-retina/*.png");

@mixin sprite-background($name) {
  background-image: sprite-url($sprites);
  background-position: sprite-position($sprites, $name);
  background-repeat: no-repeat;
  display: block;
  height: image-height(sprite-file($sprites, $name));
  width: image-width(sprite-file($sprites, $name));
  @media (-webkit-min-device-pixel-ratio: 2), (-o-min-device-pixel-ratio: 3/2), (min-device-pixel-ratio: 2) {
    // Workaround for https://gist.github.com/2140082
    @if (sprite-position($sprites, $name) != sprite-position($sprites-retina, $name)) {
      $ypos: round(nth(sprite-position($sprites-retina, $name), 2) / 2);
      background-position: 0 $ypos;
    }
    @include background-size(image-width(sprite-file($sprites, $name)) auto);
    background-image: sprite-url($sprites-retina);
  }
}

// Usage.
.mail-icon {
  @include sprite-background(mail);
}

The workaround listed on line 13 wasn't working for me... I had a sprite image with about 5 images, and the sprite generator created the 2x sprites in a different order than the 1x sprites and for whatever reason the if statement was not picking up the difference. I removed the if statement and always set the y-position for the 2x styles and that fixed it for me.