add a couple new virtual methods

panda/src/display/graphicsWindow.cxx

@@ -600,3 +600,7 @@ void GraphicsWindow::read_priorities(void) {
     }
   }
 }
+
+void GraphicsWindow::deactivate_window(void) { return; }
+void GraphicsWindow::reactivate_window(void) { return; }
+

panda/src/display/graphicsWindow.h

@@ -168,6 +168,8 @@ PUBLISHED:
 public:
   virtual void begin_frame();
   virtual void end_frame();
+  virtual void deactivate_window(void);
+  virtual void reactivate_window(void);
 
   // Statistics
   static PStatCollector _app_pcollector;