var defaultDiv = 'sky';

function setDefaultDiv(divID) {
	defaultDiv = divID;
}

window.onscroll = function () {
	y = getScrollXY()[1];
	if (document.body) {
		var larg = (document.body.clientWidth);
		var haut = (document.body.clientHeight);
	}
	else {
		var larg = (window.innerWidth);
		var haut = (window.innerHeight);
	}
	if (y < haut-600)
		moveDiv(defaultDiv,0,y);
};

function moveDiv(id,x,y) {
	var div_elem = document.getElementById(id);
	if (div_elem){
		div_elem.style.top = y+"px";
		div_elem.style.left = x+"px";
	}
}

function getScrollXY() {
  var scrOfX = 0, scrOfY = 0;
  if( typeof( window.pageYOffset ) == 'number' ) {
    //Netscape compliant
    scrOfY = window.pageYOffset;
    scrOfX = window.pageXOffset;
  } else if( document.body && ( document.body.scrollLeft || document.body.scrollTop ) ) {
    //DOM compliant
    scrOfY = document.body.scrollTop;
    scrOfX = document.body.scrollLeft;
  } else if( document.documentElement && ( document.documentElement.scrollLeft || document.documentElement.scrollTop ) ) {
    //IE6 standards compliant mode
    scrOfY = document.documentElement.scrollTop;
    scrOfX = document.documentElement.scrollLeft;
  }
  return [ scrOfX, scrOfY ];
}