function getByclass(clsName,parent){
	var oParent=parent?document.getElementById(parent):document,
		eles=[],
		elements=oParent.getElementsByTagName('*');

	for(var i=0;i<elements.length;i++){
		if(elements[i].className==clsName){
			eles.push(elements[i]);
		}
	}
	return eles;
}

window.onload=drag;

function drag(){
	var oTiltle=getByclass('login_logo_webqq','loginPanel')[0];
	oTiltle.onmousedown=fnDown;
}

function fnDown(event){
	event=event || window.event;
	var oDrag=document.getElementById('loginPanel'),
	//光标按下时光标和面板之间的距离
	disX=event.clientX-oDrag.offsetLeft,
	disY=event.clientY-oDrag.offsetTop;	
	//移动
	document.onmousmove=function(event){
		event=event || window.event;
		fnMove(event,disX,disY);
	}
}

function fnMove(e,posX,posY){
	var oDrag=document.getElementById('loginPanel'),
		l=e.clientX-posX,
		t=e.clientY-posY;
	oDrag.style.left=l+'px';
	oDrag.style.top=t+'px';
}