(function($) {
    $.extend($.fx.step,{
        backgroundPosition: function(fx) {
            if (fx.state === 0 && typeof fx.end == 'string') {
                var start = $.curCSS(fx.elem,'backgroundPosition');
                start = toArray(start);
                fx.start = [start[0],start[2]];
                var end = toArray(fx.end);
                fx.end = [end[0],end[2]];
                fx.unit = [end[1],end[3]];
            }
            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];

           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]];
           }
        }
    });
})(jQuery);

(function($) {
    jQuery.fn.backgroundPosition = function() {
        var p = $(this).css('background-position');
        if (typeof(p) == 'undefined') {
            return $(this).css('background-position-x') + ' ' + $(this).css('background-position-y');
        } else {
           return p;
        }
    };
})(jQuery);

$('#menu-desc > img').preload();

$(function(){
    $('#menu > li').bind('mouseenter', function() {
        var el = $(this);
        
        if (typeof(el.data('position')) == 'undefined') {
            el.data('position', el.backgroundPosition());
        }
        
        el.css({backgroundPosition: el.backgroundPosition()});
        
        $('#menu_' + el.attr('class') + '_desc').fadeIn(500);
        
        el.stop().animate({
            backgroundPosition: '(0px 0px)'
        }, 500);
        
    }).bind('mouseleave', function() {
        var el = $(this);
        
        el.css({backgroundPosition: el.backgroundPosition()});
        
        $('#menu_' + el.attr('class') + '_desc').fadeOut(500);
        
        el.stop().animate({
            backgroundPosition: "(" + el.data('position') + ")"
        }, {duration: 500});
    });
});