jquery 元素相对定位

/**
*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)