var TimeToFade = 1000.0;
var pocet = document.getElementById("pocetheaders").value;
var randomnumber=Math.floor(Math.random()*pocet);
var predchoziHeader=randomnumber;
var elem = document.getElementById('ThreePhotos');
var IE = true;



function getInternetExplorerVersion()
// Returns the version of Internet Explorer or a -1
// (indicating the use of another browser).
{
  var rv = -1; // Return value assumes failure.
  if (navigator.appName == 'Microsoft Internet Explorer')
  {
    var ua = navigator.userAgent;
    var re  = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
    if (re.exec(ua) != null)
      rv = parseFloat( RegExp.$1 );
  }
  return rv;
}

var ver = getInternetExplorerVersion();
if ( ver > -1 )
  {
    if ( ver <= 8.0 ) IE = false;    
  }


elem.style.background = 'url(./public/design/headers/hd' + randomnumber +'.png)';

function fade(eid)
{
  var element = document.getElementById(eid);
  if(element == null)
    return;
   
  if(element.FadeState == null)
  {
    if(element.style.opacity == null 
        || element.style.opacity == '' 
        || element.style.opacity == '1')
    {
      element.FadeState = 2;
    }
    else
    {
      element.FadeState = -2;
    }
  }
    
  if(element.FadeState == 1 || element.FadeState == -1)
  {
    element.FadeState = element.FadeState == 1 ? -1 : 1;
    element.FadeTimeLeft = TimeToFade - element.FadeTimeLeft;
  }
  else
  {
    element.FadeState = element.FadeState == 2 ? -1 : 1;
    element.FadeTimeLeft = TimeToFade;
    setTimeout("animateFade(" + new Date().getTime() + ",'" + eid + "')", 33);
  }  
}

function animateFade(lastTick, eid)
{  
  var curTick = new Date().getTime();
  var elapsedTicks = curTick - lastTick;
  
  var element = document.getElementById(eid);
 
  if(element.FadeTimeLeft <= elapsedTicks)
  {
    element.style.opacity = element.FadeState == 1 ? '1' : '0';
    element.style.filter = 'alpha(opacity = ' 
        + (element.FadeState == 1 ? '100' : '0') + ')';
    element.FadeState = element.FadeState == 1 ? 2 : -2;
    return;
  }
 
  element.FadeTimeLeft -= elapsedTicks;
  var newOpVal = element.FadeTimeLeft/TimeToFade;
  if(element.FadeState == 1)
    newOpVal = 1 - newOpVal;

  element.style.opacity = newOpVal;
  element.style.filter = 'alpha(opacity = ' + (newOpVal*100) + ')';
  
  setTimeout("animateFade(" + curTick + ",'" + eid + "')", 33);
}


function ChangeThreePhotos() {
if(IE) {            
fade('ThreePhotos');
}
randomnumber=Math.floor(Math.random()*pocet);

while (predchoziHeader == randomnumber) {
randomnumber=Math.floor(Math.random()*pocet);
}

predchoziheader=randomnumber;
setTimeout("elem.style.background = 'url(./public/design/headers/hd' + randomnumber +'.png)'",1250);
if(IE) {  
setTimeout("fade('ThreePhotos')",2500);
}
}   

window.setInterval("ChangeThreePhotos()",10000);