Get background-position from Compass magic sprites in em

Get background-position from Compass magic sprites in em

/** 
 * @subsection Get Sprites position in EM
 * @author Marie Guillaumet
 */
@mixin em-sprite-position($map, $sprite, $context: $fs, $offset-x: 0, $offset-y: 0)
{

	/** Thank you @pioupiouM! */
	$position: sprite-position($map, $sprite, $offset-x, $offset-x);
	$x: nth($position, 1);
	$y: nth($position, 2);
	
	@if "%" == unit($offset-x)
	{
		background-position: $offset-x em($y,$context);
	}
	@else if "%" == unit($offset-y)
	{
		background-position: em($x,$context) $offset-y;
	}
	@else
	{
		background-position: em($x,$context) em($y,$context);
	}
}