if (window.screen) {
  altura = screen.height;
  anchura = screen.width;
}
else {
  altura = 600;
  anchura = 800;
}

function getAbsX(obj)
{
  var obj=document.getElementById(obj);
  var leftOffset = 0;
  if (obj.offsetParent)
  {
    while (obj.offsetParent)
    {
     leftOffset += obj.offsetLeft;
     obj = obj.offsetParent;
    }
  }
  else if (obj.x) //for NN4
  {
     leftOffset = obj.x;
  }
  return leftOffset;
}
          
function getAbsY(obj)
{
  var obj=document.getElementById(obj);
  var topOffset = 0;
  if (obj.offsetParent)
  {
    while (obj.offsetParent)
    {
      topOffset += obj.offsetTop;
      obj = obj.offsetParent;
    }
  }
  else if (obj.y) // for NN4
  {
      topOffset = obj.y;
  }
  return topOffset;
}