public function setViewport($width = null, $height = null)
{
if ($width == null) {
unset($this->viewport);
}
if (is_string($width) && in_array($width, $this->viewportMap)) {
$vp = $this->viewportMap[$width];
$width = $vp['width'];
$height = $vp['height'];
}
$this->viewport = array('width' => $width, 'height' => $height);
}