jquery 元素相对定位代码

/** 
*jQuery rposition 
*fix:要定位的元素 
*rel：相对定位的元素 
*options:{},align:左右对齐;vlign:垂直对齐;xleft:水平补给值;xleft:垂直补给值;adjust:是否相对窗口自动调整;rwindow:定位相对于窗口(align&vlign为center时垂直或水平居中); 
*/ 
(function(win,$){ 
win.rposition=function(fix,rel,options){ 
var rectLeft,rectTop,rectH=fix.outerHeight(),rectW=fix.outerWidth(),wh=$(window).height(),ww=$(window).width(), 
sT=$(document).scrollTop(),sL=$(document).scrollLeft(), 
defaults={ 
align:"left", 
vlign:"top", 
xleft:0, 
xtop:0, 
adjust:true, 
rwindow:false 
}, 
options = $.extend(defaults, options); 
var rectRel={ 
l:$(rel).offset().left, 
t:$(rel).offset().top, 
w:$(rel).outerWidth(), 
h:$(rel).outerHeight() 
}; 
switch(options.align){ 
case "left": 
rectLeft=rectRel.l;break; 
case "right": 
rectLeft=rectRel.l+rectRel.w;break; 
case "center": 
rectLeft=rectRel.l+rectRel.w/2;break; 
case "rleft": 
rectLeft=rectRel.l-rectW;break; 
default: 
rectLeft=rectRel.l; 
}; 
switch(options.vlign){ 
case "top": 
rectTop=rectRel.t;break; 
case "center": 
rectTop=rectRel.t+rectRel.h/2;break; 
case "vbottom": 
rectTop=rectRel.t-rectH; break; 
case "bottom": 
default: 
rectTop=rectRel.t+rectRel.h; 
}; 
if(options.rwindow){ 
if(options.align=="center")rectLeft=(ww-rectW)/2+sL; 
if(options.vlign=="center")rectTop=(wh-rectH)/2+sT; 
}; 
if(options.adjust){ 
if(rectLeft+rectW>ww+sL){rectLeft-=(rectLeft+rectW)-(ww+sL)} 
if(rectTop+rectH>wh+sT){rectTop=rectRel.t-rectH;} 
}; 
$(fix).css({"left":rectLeft+options.xleft,"top":rectTop+options.xtop}); 
} 
})(window,jQuery)