public function get_renderer(moodle_page $page, $component, $subtype = null, $target = null) {
        if (is_null($this->rf)) {
            $classname = $this->rendererfactory;
            $this->rf = new $classname($this);
        }

        return $this->rf->get_renderer($page, $component, $subtype, $target);
    }