SCSS and Compass retina sprites

mixin.scss

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

$icons-spacing: 5px;
$sprites : sprite-map("icons/*.png");

@mixin retina-sprite($name) {
	$name : $name;
	background-image: sprite-url($sprites);
	width: image-width(sprite-file($sprites, $name)) / 2;
	height: image-height(sprite-file($sprites, $name)) / 2;
	$ypos: nth(sprite-position($sprites, $name), 2) / 2;
	background-position: 0 $ypos;
	@include background-size(ceil(image-width(sprite-path($sprites)) / 2), auto);
}

usage: "@include retina(spritename);"