var timer = null;
var animpanewidth = 0;
var animoffset = -1;
var curpos = 0;
var animspeed = 30;
var animrun = 1;

// the slider width is 2* the overhang
// overhang = image width - window width

onload = function()
{
	animpanewidth = document.getElementById("slider").offsetWidth;
	//alert(animpanewidth/2);
	timer = setInterval("anim()", animspeed);
}

onunload = function()
{
	if(timer) clearInterval(timer);
}

function
anim()
{
	var elem = document.getElementById("slider");
	
	if(curpos + animoffset <= -animpanewidth/2)
	{
    animoffset = -animoffset;
	}
	if(curpos + animoffset > 0 )
	{
    animoffset = -animoffset;
	}
		elem.style.display = "block";
		elem.style.left  = (curpos += animoffset) + "px";
}

function
toggle_anim()
{
 if(animrun > 0)
 {
  animrun = 0;
	if(timer) clearInterval(timer);
 }
  else
  {
  animrun = 1;
  animoffset = -animoffset;
  timer = setInterval("anim()", animspeed);
  }
}