code: private JFrame initMainFrame()
      {
          final String title = getTitle();
          final JFrame jframe = new JFrame(title, conf);
          jframe.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
          jframe.addWindowListener(new WindowAdapter()
          {
              @Override
              public void windowClosing(WindowEvent event)
              {
                  listeners.forEach(ScreenListener::notifyClosed);
              }
          });
          jframe.setResizable(false);
          jframe.setUndecorated(false);
          jframe.setIgnoreRepaint(true);
  
          return jframe;
      }
docs: Initialize the main frame.
  
  @return The created main frame.
  @throws LionEngineException If the engine has not been started.