public void initApp(){
// (...)
            XCgui.initGUI_menu_elements();

            // la loop principale
            while (XCgame.device.Run() && !XCgame.appEnd)
            {
                if (XCgame.inMenu)
                {
                    // affichage menu
                    XCgame.videoDriver.BeginScene(true, false, XCgui.GUIBackColor);  // Zbuffer false car gui == 2D
                    XCgui.guienv.DrawAll();
                    XCgame.videoDriver.EndScene();
                }
                else if (XCgame.inGame)
                {
                    // affichage jeu
                    XCgame.videoDriver.BeginScene(true, true, XCgame.GameBackColor);
                    XCgame.ingameText.Draw();
                    XCgame.device.SceneManager.DrawAll();
                    XCgame.videoDriver.EndScene();
                }
                else if (XCgame.inOptions)
                {
                    // affichage des options
                    XCgame.videoDriver.BeginScene(true, false, XCgui.GUIBackColor);
                    XCgui.guienv.DrawAll();
                    XCgame.videoDriver.EndScene();
                }
                else
                {
                    // juste au cas où l'on oubli de renverser les flags inMenu/inOptions  qqpart ^^
                    Console.WriteLine("la loop principale ne sait pas où se brancher. XCgame.inMenu = true;");
                    XCgame.inMenu = true;
                }
            }
}
static public bool OnEvent(Event ev){
           {...}
                    else if (ev.Caller.ID == (int)XCgui.GUIItems.PlaySingleXC)
                        {
                            Console.WriteLine("Vous voulez jouer.");
                            // enleve les boutons et met les flags d'aff au jeu
                            //XCgui.guienv.Dispose();  // on pourra le réinitialiser lorsque necessaire...
                            XCgui.disposeGUI_menu_elements();
                            XCgame.ingameText.Visible = true;
                            XCgame.inMenu = false;
                            XCgame.inOptions = false;
                            XCgame.inGame = true;
                            return false;
                        }
                    else if (ev.Caller.ID == (int)XCgui.GUIItems.Options)
                        {
                            Console.WriteLine("Vous allez dans les options.");
                            XCgui.XCLogo.Enabled = true;
                            XCgui.XCLogo.Visible = true;
                            XCgui.playSingleButton.Enabled = false;
                            XCgui.playSingleButton.Visible = false;
                            XCgui.playMultiButton.Enabled = false;
                            XCgui.playMultiButton.Visible = false;
                            XCgui.optionsButton.Enabled = false;
                            XCgui.optionsButton.Visible = false;
                            XCgui.exitButton.Enabled = false;
                            XCgui.exitButton.Visible = false;
                            XCgui.optionsDoneButton.Enabled = true;
                            XCgui.optionsDoneButton.Visible = true;
                            
                            XCgame.ingameText.Visible = false;
                            XCgame.inMenu = false;
                            XCgame.inGame = false;
                            XCgame.inOptions = true;
                            return false;
                        } // fin ev.Type == EventType.GUIEvent
            else if (ev.Type == EventType.KeyInputEvent && XCgame.inGame)
            {
                switch (ev.KeyCode)
                {
                    case KeyCode.Escape:
                        // enable the useful buttons...
                        XCgui.initGUI_menu_elements();
                        XCgame.ingameText.Visible = false;
                        XCgame.inGame = false;
                        XCgame.inOptions = false;
                        XCgame.inMenu = true;
                        return false;
                    default:
                        return false;
                }
            }
            return false;
        }  // fin device_OnEvent() */

            public static void disposeGUI_menu_elements(){
                Console.WriteLine("disposeGUI_menu_elements()");
                exitButton.Remove();
                optionsDoneButton.Remove();
                optionsButton.Remove();
                playMultiButton.Remove();
                playSingleButton.Remove();
                XCLogo.Remove();
                guienv = null;
            }