Re: Mouse Clicks in a Drawing Area

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 4 Feb 2014 11:08:30 +0100, ldries46 wrote:

> I now het changed the Add_Events into Set_Events (within the first code 
> listing but the result is the same, nothing happens.
> I had done it that way before but
> 
> http://askubuntu.com/questions/157290/how-to-draw-on-mouse-click-in-gtk-drawingarea-using-pygi
> 
> suggested the add_events routine. That code is now
> 
> Set_Events(Sudoku_Area, BUTTON_PRESS_MASK);
> CR := Create(Get_Window (Sudoku_Area));
> Event_Cb.Connect (Sudoku_Area, "draw",
>                   Event_Cb.To_Marshaller 
> (On_Area_Draw'Unrestricted_Access));
> Event_Cb.Connect (Sudoku_Area, "button_press_event",
>                   Event_Cb.To_Marshaller 
> (On_Button_Press'Unrestricted_Access));
> 
> The problem stays the same as.
> 
Typically for mouse tracking you would do:

Sudoku_Area.Set_Can_Focus (True);
Sudoku_Area.Set_Events
(  Exposure_Mask
or Leave_Notify_Mask
or Button_Press_Mask
or Button_Release_Mask
or Pointer_Motion_Mask
or Pointer_Motion_Hint_Mask
);

> Just for extra information the code od On_Button_Press:
> 
> function On_Button_Press (Object : access Gtk_Drawing_Area_Record'Class; 
> event : Gdk_Event) return boolean is
>    pragma Unreferenced (Object);
> begin
>    ev := event.Button;  -- line where the breakpoint is invoked
>    nb := ev.Button;
>    if nb = 1 then
>       x := ev.X;
>       y := ev.Y;
>    end if;
>    return nb = 1;
> end On_Button_Press;

You would use Get_Button to determine which mouse button was pressed.

P.S. It is not a good idea to use global variables as you do. For this
reason Connect operations to attach callbacks have very limited use. In
most cases you should instantiate User_Callback or User_Return_Callback to
be able to pass an additional parameter to the handler.

P.P.S. You should not use debugger with GTK. It works very rarely if at
all. Do tracing instead. And you must always handle all exceptions within
signal handlers. Propagation out of a handler will certainly corrupt stack
and crush the program. Use Glib.Messages it is a great help.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de