window.onscroll = function(){
	move_btn("floatmenu");
};


var timerID;
var ease_scrolling=0;

function move_btn(id){
	if(ease_scrolling==0){
		btn=document.getElementById(id);
		if(btn!=null){
			set_btn(btn);
			clearInterval(timerID);
			timerID=setInterval("set_btn(btn)", 5);
		}
	}
}



function set_btn(btn){
	y = document.body.scrollTop || document.documentElement.scrollTop;
	dheight=window.innerHeight||document.documentElement.clientHeight;
	//400ってのはボタンのある位置、100ってのはフッタの高さ。
	if(dheight<100){
		y=y+dheight-100;
	}
	y=Math.max(y-100,0);
	btnorg=btn.style.top;
	btn.style.top=(y-parseInt(btn.style.top))/15+parseInt(btn.style.top)+"px";
	if(btnorg==btn.style.top){
			clearInterval(timerID);
	}
}