Retina sprite for Compass

retina-sprite.scss

@import "compass/utilities/sprites";         // Include compass sprite helpers
@import "compass/css3/background-size";      // Include helper to calc background size

// background sprite for retina
// Use:
// $sprites2x: sprite-map("sprites/*.png", $spacing: 2px);
// .icon-new {
// 		@include retina-sprite(icon-new, $sprites2x);
// }
@mixin retina-sprite($name, $sprites2x, $padding: 0) {
  background-repeat: no-repeat;

  @if $padding > 0 {
    padding: $padding;
  }

  $pos: sprite-position($sprites2x, $name, -$padding * 2, -$padding * 2);
  background-image: sprite-url($sprites2x);
  background-position: nth($pos, 1) nth($pos, 2) / 2;
  @include background-size(ceil(image-width(sprite-path($sprites2x)) / 2) auto);
}