class OffCanvasRenderer

class OffCanvasRenderer extends DialogRenderer {
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * The position to render the off-canvas dialog.
     *
     * @var string
     */
    protected $position;
    
    /**
     * Constructs a new OffCanvasRenderer.
     *
     * @param \Drupal\Core\Controller\TitleResolverInterface $title_resolver
     *   The title resolver.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     * @param string $position
     *   (optional) The position to render the off-canvas dialog.
     */
    public function __construct(TitleResolverInterface $title_resolver, RendererInterface $renderer, $position = 'side') {
        parent::__construct($title_resolver, $renderer);
        $this->renderer = $renderer;
        $this->position = $position;
    }
    
    /**
     * {@inheritdoc}
     */
    public function renderResponse(array $main_content, Request $request, RouteMatchInterface $route_match) {
        $response = new AjaxResponse();
        // First render the main content, because it might provide a title.
        $content = $this->renderer
            ->renderRoot($main_content);
        // Attach the library necessary for using the OpenOffCanvasDialogCommand and
        // set the attachments for this Ajax response.
        $main_content['#attached']['library'][] = 'core/drupal.dialog.off_canvas';
        $response->setAttachments($main_content['#attached']);
        // If the main content doesn't provide a title, use the title resolver.
        $title = isset($main_content['#title']) ? $main_content['#title'] : $this->titleResolver
            ->getTitle($request, $route_match->getRouteObject());
        // Determine the title: use the title provided by the main content if any,
        // otherwise get it from the routing information.
        $options = $request->request
            ->get('dialogOptions', []);
        $response->addCommand(new OpenOffCanvasDialogCommand($title, $content, $options, NULL, $this->position));
        return $response;
    }

}