var timer = null;
var init = false;
var top_limit = 0;
var btn_height = 96;
function move_gotop()
{
	if(!init){
		init = true;
		init_pos();
	}
	
	var _body = document.documentElement || document.body;
	var nowtop = eval(document.getElementById("btn_top").style.top.replace("px",""));
	var scrollY = _body.scrollTop || _body.scrollTop;
	scrollY += _body.clientHeight / 2;
	
	var vector = (scrollY - nowtop) / 10;
	if(scrollY > nowtop && vector < 2){
		vector = 2;
	}else if(scrollY < nowtop && vector > -2){
		vector = -2;
	}
	var newtop = nowtop+vector;
	if((scrollY >= nowtop && newtop >= scrollY)||(scrollY <= nowtop && newtop <= scrollY)){
		newtop = scrollY;
		clearTimeout(timer);
		timer = null;
	}else{
		timer = setTimeout("move_gotop()",1);
	}
	if(newtop < top_limit){
		newtop = top_limit;
	}
	document.getElementById("btn_top").style.top = newtop+"px";
}

function set_gotop()
{
	if(!timer){
		timer = setTimeout("move_gotop()",1);
	}
}

function init_pos()
{
	var elem = document.getElementById("plan01");
	var _width = elem.offsetWidth;
	var _left = 0;
	var _top = 0;
	do{
		_left += elem.offsetLeft;
		_top += elem.offsetTop;
		elem = elem.offsetParent;
	}while(elem);
	top_limit = _top+10;
	document.getElementById("btn_top").style.left = _left+_width-53+"px";
	document.getElementById("btn_top").style.top = _top+"px";
	document.getElementById("btn_top").style.display = "block";
}

function init_left()
{
	var elem = document.getElementById("plan01");
	var _width = elem.offsetWidth;
	var _left = 0;
	do{
		_left += elem.offsetLeft;
		elem = elem.offsetParent;
	}while(elem);
	document.getElementById("btn_top").style.left = _left+_width-53+"px";
}

if(window.attachEvent){
	window.attachEvent("onload",move_gotop);
	window.attachEvent("onresize",init_left);
	window.attachEvent("onscroll",set_gotop);
}else if(window.addEventListener){
	window.addEventListener("load",move_gotop,false);
	window.addEventListener("resize",init_left,false);
	window.addEventListener("scroll",set_gotop,false);
}