function getViewportSize()
{
  var size = [0, 0];

  if (typeof window.innerWidth != 'undefined')
  {
    size = [
        window.innerWidth,
        window.innerHeight
    ];
  }
  else if (typeof document.documentElement != 'undefined'
      && typeof document.documentElement.clientWidth !=
      'undefined' && document.documentElement.clientWidth != 0)
  {
    size = [
        document.documentElement.clientWidth,
        document.documentElement.clientHeight
    ];
  }
  else
  {
    size = [
        document.getElementsByTagName('body')[0].clientWidth,
        document.getElementsByTagName('body')[0].clientHeight
    ];
  }

  return size;
}