//We wrap all the code in an object so that it doesn't interfere with any other code
var scroller = {
  init:   function() {

	//collect the variables
	scroller.docH = document.getElementById("scrollcontent").offsetHeight;
	scroller.contH = document.getElementById("scrollport").offsetHeight;
	scroller.scrollAreaH = document.getElementById("scrollarea").offsetHeight;
	  
	//calculate height of scroller and resize the scroller div
	//(however, we make sure that it isn't to small for long pages)
	scroller.scrollH = (scroller.contH * scroller.scrollAreaH) / scroller.docH;
	if(scroller.scrollH < 15) scroller.scrollH = 15;
	document.getElementById("scroller").style.height = Math.round(scroller.scrollH) + "px";
	
	//what is the effective scroll distance once the scoller's height has been taken into account
	scroller.scrollDist = Math.round(scroller.scrollAreaH-scroller.scrollH);
	
	//make the scroller div draggable
	Drag.init(document.getElementById("scroller"),null,0,0,-1,scroller.scrollDist);
	
	//add ondrag function
	document.getElementById("scroller").onDrag = function (x,y) {
	  var scrollY = parseInt(document.getElementById("scroller").style.top);
	  var docY = 0 - (scrollY * (scroller.docH - scroller.contH) / scroller.scrollDist);
	  document.getElementById("scrollcontent").style.top = docY + "px";
	}
  }
}

onload = scroller.init;