I'm having a problem with fl_message when it appears in an Fl_Gl_Window. When it returns, it (usually, but not always) leaves part of its window visible in the Fl_Gl_Window, but ONLY there. This suggests that, for some reason, I'm not responding to some system request for repainting the Fl_Gl_Window ... doesn't it? Yet, if I invalidate and redraw the Fl_Gl_Window immediately upon return from fl_message, it may or may not clear the
fl_message window - usually not. Any ideas?

DBG

When the OS closes your dialog box and the previously obscured area touches your GL window, the draw() function of your window will be called. Make sure that it is actually called (add a printf()), and if that is the case, make sure that you actually draw something.

Oh, if you do heavy calculations after closing the dialog box, you windows will now be redrawn until your process returns to Fl::run().