Retina Sprite mixin using SCSS and COMPASS

retina-sprite.scss

// COMPASS
@import "compass/utilities/sprites"; 
@import "compass/css3/background-size"; 

// Import Images
$sprites: sprite-map("sprites/*.png");
$sprites2x: sprite-map("sprites-retina/*.png");

@mixin sprite($name) {
	@include retina-sprite($name, $sprites, $sprites2x);
}
  
@mixin retina-sprite($name, $sprites, $sprites2x, $dimensions: true) {

	display: block;
	background-image: sprite-url($sprites);
	background-position: sprite-position($sprites, $name);
	background-repeat: no-repeat;

	@if $dimensions == true {
		@include sprite-dimensions($sprites, $name);	
	}

	@media (-webkit-min-device-pixel-ratio: 1.5), (min--moz-device-pixel-ratio: 1.5), (-o-min-device-pixel-ratio: 3/2), (min-device-pixel-ratio: 1.5) {
		& {
			$pos: sprite-position($sprites2x, $name);
			background-image: sprite-url($sprites2x);
			background-position: nth($pos, 1) nth($pos, 2)/2;
			@include background-size(ceil(image-width(sprite-path($sprites2x)) / 2), auto);			
		}
	}
}