(function($) {
	
	function toArray(strg){
		strg = strg.replace(/left|top/g,'0px');
		strg = strg.replace(/right|bottom/g,'100%');
		strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g,"$1px$2");
		var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
		return [parseFloat(res[1],10),res[2],parseFloat(res[3],10),res[4]];
	}
	
	$.fx.step. backgroundPosition = function(fx) {
		if (!fx.bgPosReady) {
			
			var start = $.curCSS(fx.elem,'backgroundPosition');
			if(!start){//FF2 no inline-style fallback
				start = '0px 0px';
			}
			
			start = toArray(start);
			fx.start = [start[0],start[2]];
			
			var end = toArray(fx.options.curAnim.backgroundPosition);
			fx.end = [end[0],end[2]];
			
			fx.unit = [end[1],end[3]];
			fx.bgPosReady = true;
		}
		
		var nowPosX = [];
		nowPosX[0] = ((fx.end[0] - fx.start[0]) * fx.pos) + fx.start[0] + fx.unit[0];
		nowPosX[1] = ((fx.end[1] - fx.start[1]) * fx.pos) + fx.start[1] + fx.unit[1];           
		fx.elem.style.backgroundPosition = nowPosX[0]+' '+nowPosX[1];

	};
})(jQuery);