// the <div> containers

// - "mainnav" (nav itself)

// - "DivBottom" (bottom of the "mainnav", to calculate nav height)

// - "footer"

// must be declared as position:relative/absolute, so that findPos() can calculate

// their absolute position.

// The minimum pos is declared hard-coded (feel free to change that).



function findPos(objId) {

    var obj     = findObj(objId);

	var curleft = curtop = 0;

	if (!obj) {

	   throw "object with id " + objId + " does not exist in this document";

	}

	if (obj.offsetParent) {

		do {

			curleft += obj.offsetLeft;

			curtop  += obj.offsetTop;

		} while (obj = obj.offsetParent);

	}

	return [curleft, curtop];

}



function findObj(objId) {

    return document.getElementById(objId);

}



function findScrollY() {

    var sp = document.body.parentNode.scrollTop;

    if (sp == 0) sp = document.body.scrollTop;

    return sp;

}



function autoscroll() {

    var mainnav     = findPos("mainnav");

    var divbottom   = findPos("DivBottom");

    var footer      = findPos("footer");

    var navHeight   = divbottom[1] - mainnav[1];

    //alert(navHeight);

    var minPosY     = 156; // top banner height

    var maxPosY     = footer[1] - navHeight;

    var scrollY     = findScrollY();

    //alert(scrollY + "\n" + contentwrap);

    var navObj      = findObj("mainnav");

    if (scrollY > minPosY) {

	    var newPosY     = Math.min(maxPosY, scrollY - minPosY) + "px";

	    //alert(navObj + "\n" + newPosY);

	    navObj.style.top = newPosY;

    } else {

        findObj("mainnav").style.top = 0 + "px";

    }

}



function autoscrollInit() {

    window.onscroll = autoscroll;

}