function screenSize() {
   
   if (!isset($_SESSION['screen_width']) and !isset($_SESSION['screen_height'])) {
      session_start();
   }    

   if(isset($_SESSION['screen_width']) AND isset($_SESSION['screen_height'])){
      $arrayScreenSize = array('width' => $_SESSION['screen_width'], 'height' => $_SESSION['screen_height']);
   } else if(isset($_REQUEST['width']) AND isset($_REQUEST['height'])) {
       $_SESSION['screen_width'] = $_REQUEST['width'];
       $_SESSION['screen_height'] = $_REQUEST['height'];
       header('Location: ' . $_SERVER['PHP_SELF']);
      $arrayScreenSize = array('width' => $_SESSION['screen_width'], 'height' => $_SESSION['screen_height']);
   } else {
       echo '<script type="text/javascript">window.location = "' . $_SERVER['PHP_SELF'] . '?width="+screen.width+"&height="+screen.height;</script>';
       $arrayScreenSize = array('width' => "", 'height' => "");
   }

   return $arrayScreenSize;
}