[Octave-bug-tracker] [bug #60509] First initialization of graphics subsystem switches graphics_toolkit when octave-cli used

[Rik]

Follow-up Comment #10, bug #60509 (project octave):

In graphics.cc, the constructor for gh_manager is


gh_manager::gh_manager (octave::interpreter& interp)
  : m_interpreter (interp), m_handle_map (), m_handle_free_list (),
    m_next_handle (-1.0 - (rand () + 1.0) / (RAND_MAX + 2.0)),
    m_figure_list (), m_graphics_lock (),  m_event_queue (),
    m_callback_objects (), m_event_processing (0)
{
  m_handle_map[0] = graphics_object (new root_figure ());

  octave::gtk_manager& gtk_mgr = octave::__get_gtk_manager__ ("gh_manager");

  // Make sure the default graphics toolkit is registered.
  gtk_mgr.default_toolkit ();
}


Problem #1 is that default_toolkit is a read-only function defined in
gtk-manager.h


    std::string default_toolkit (void) const { return dtk; }


It just returns a string which is discarded in the function above.

Is it a requirement that gh_manager exist before figures can be plotted?  If
so then this would make a natural point to force at least one toolkit to be
loaded, or error out.  But maybe we shouldn't even do this.  If a user is
going to use gnuplot all of the time then there is no point loading the 'qt'
or 'fltk' toolkits.

The toolkit needs to be stored on a per-figure basis, since it is switchable. 
But the initialization needs to happen just once per toolkit.  Maybe we need
to store 1 bit of state information in gtk_manager that says whether any
toolkit has been initialized?  It might make even more sense to map this
functionality on to a test for whether loaded_graphics_toolkits is empty or
not.  If toolkits were unregistered this would naturally track the current
status.

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