// Pro zmenu rychlosti prolinani staci upravit nasledujici dve hodnoty ---------
var defaultInterval = 50;
var longInterval = 1000;
//------------------------------------------------------------------------------

var Timer;
var pos = 0;
var opa = 0;
var up = true;

addEvent(window, "load", initWindow);

function addEvent(el, event, func) {
  if (el.addEventListener) {
    el.addEventListener (event, func, false);
  } else {
    el.attachEvent ("on" + event, func);
  }
}

function initWindow() {
  Timer = window.setTimeout("opacity()", defaultInterval);
}

function opacity() {
  var el = document.getElementById('changing');
  if(el) {
    if(up) {
      opa += 0.1;
    } else {
      opa -= 0.1;
    }
    el.style.opacity = opa;
    el.style.filter = "alpha(opacity=" + (100 * opa) + ")";
    if(opa >= 1) {
      up = false;
      opa = 1.0;
      window.setTimeout("opacity()", longInterval);
      return;
    } else if(opa <= 0) {
      up = true;
      opa = 0.0
      roll(el);
    }
  }
  window.setTimeout("opacity()", defaultInterval);
}

function roll(el) {
  pos -= 44;
  el.style.backgroundPosition = "0 " + pos + "px";
  if(pos == -176) {
    pos = 44;
  }
}