// Browser Checker

function browserCheck(){ 

	this.ver=navigator.appVersion

	this.agent=navigator.userAgent

	this.dom=document.getElementById?1:0

	this.opera6=((this.agent.indexOf("Opera 6")>-1) && this.dom)?1:0;

	this.ie5=((this.ver.indexOf("MSIE 5")>-1) && this.dom && !this.opera6)?1:0; 

	this.ie6r=((this.ver.indexOf("MSIE 6")>-1) && this.dom && (document.compatMode == "BackCompat"))?1:0;

	this.ie6s=((this.ver.indexOf("MSIE 6")>-1) && this.dom && (document.compatMode == "CSS1Compat"))?1:0;

	this.ie4=(document.all && !this.dom)?1:0;

	this.ie=(this.ie4||this.ie5||this.ie6r||this.ie6s)?1:0;

	this.mac=(this.agent.indexOf("Mac")>-1)?1:0;

	this.ns6=(this.dom && (parseInt(this.ver) >= 5)) ?1:0; 

	this.ns4=(document.layers && !this.dom)?1:0;

	this.ns=(this.ns4||this.ns6)?1:0;

	this.bw5=(this.ie5||this.ie6r)?1:0;

	this.bw6=(this.ie6s||this.ns6||this.opera6)?1:0;

	this.bw=(this.ie6r||this.ie6s||this.ie5||this.ns6||this.opera6)?1:0;

	return this;

}



// Global Variables

var ENMarginTop, ENMarginBottom, ENTop;

var ENDivName, ENObject, ENCurrentY;

var InitY = 0;

function ENInit(id, mt, mb, tp) // DIVid, margin-top, margin-bottom, position-top,

{

	bw=new browserCheck;

	if (bw.bw) {

		ENDivName = bw.bw5 ? document.all(id) : bw.bw6 ? document.getElementById(id) : 0;

		ENObject = ENDivName.style;

		ENObject.position = 'absolute';

		ENMarginTop = mt ? mt : 0; // 引数mt省略時は0

		ENMarginBottom = mb ? mb : 0; // 引数mb省略時は0

		ENCurrentY = ENTop = tp ? tp : ENDivName.offsetTop; //引数tp省略時は自動取得

		InitY = ENCurrentY;

		ENSmoothMove();

	} 

}



function ENSmoothMove()

{

	var winh = bw.ie6s ? document.documentElement.clientHeight : (bw.ns6||bw.opera6) ? innerHeight : bw.bw5 ? document.body.clientHeight : 0 ;

	var yt = bw.ie6s ? document.documentElement.scrollTop : bw.bw5 ? document.body.scrollTop : (bw.ns6||bw.opera6) ? window.pageYOffset : 0;

	var divh = ENDivName.offsetHeight;



	if (winh >= ENMarginTop + divh + ENMarginBottom) {

		yt = Math.max(yt + ENMarginTop, ENTop);

	} else {

		// 下へ向かう力

		var yt1 = Math.max(yt + ENMarginTop, ENTop);

		var f1 = (yt1 > ENCurrentY) ? 1 : 0;

		// 上へ向かう力

		var yt2 = yt - (divh + ENMarginBottom - winh);

		yt2 = Math.max(yt2, ENTop);

		var f2 = (yt2 < ENCurrentY) ? 1 : 0;

		// 両方の力が働いている場合は相殺

		if (f1 && f2) yt = ENCurrentY;

		else yt = f2 ? Math.max(yt1, yt2) : Math.min(yt1, yt2);

	}



	if (yt != ENCurrentY) {

		// 目標値に徐々に近づける

		var vy = (yt - ENCurrentY) * 0.25;

		if (Math.abs(vy) < 1) vy = (vy > 0) ? 1 : (vy < 0) ? -1 : 0;

		ENCurrentY += Math.round(vy);

		if( ENCurrentY > 200 )

		ENCurrentY += 10;

		ENObject.top = ENCurrentY + 'px';

	}

	setTimeout('ENSmoothMove()', 20);

}