// JavaScript Document

 (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(){
                var nav = $('.nav'),
                    navHeight = $('a:eq(0)',nav).height(),
                    imgSrcDirectory = 'images/',
                    imgSrcPrefix = 'nav-',
                    imgSrcSuffix = '.png';
                $('li',nav).each(function(){
                    $(this).css({
                        height: $(this).height(),
                        overflow: 'hidden'
                    });
                }).children('a').each(function(){
                    var imgSRC = imgSrcDirectory + imgSrcPrefix + $(this).attr('class') + imgSrcSuffix,
                        paddingTop = $(this).css('paddingTop').replace('px',''),
                        parentHeight = $(this).parent().height();
                    $(this).css({
                        backgroundImage: 'url(' + imgSRC + ')',
                        backgroundRepeat: 'no-repeat',
                        backgroundPosition: '50% -' + (parentHeight+2) + 'px'
                    }).hover(function(){
                        $(this).stop().animate({
                            paddingTop: '+=' + parentHeight + 'px',
                            backgroundPosition:'(50% 0)'
                        });
                    },function(){
                        $(this).stop().animate({
                            paddingTop:paddingTop,
                            backgroundPosition: '(50% -' + (parentHeight+2) + 'px)'
                        });
                    });
                });
            });