jquery.backgroundPosition.js

/**
 * @author Alexander Farkas
 * v. 1.1
 */

(function($){
	
	if(!document.defaultView || !document.defaultView.getComputedStyle){
		var oldCurCSS = jQuery.curCSS;
		jQuery.curCSS = function(elem, name, force){
			if(name !== 'backgroundPosition' || !elem.currentStyle || elem.currentStyle[ name ]){
				return oldCurCSS.apply(this, arguments);
			}
			var style = elem.style;
			if ( !force && style && style[ name ] ){
				return style[ name ];
			}
			return oldCurCSS(elem, 'backgroundPositionX', force) +' '+ oldCurCSS(elem, 'backgroundPositionY', force);
		};
	}
})(jQuery);

(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);