Re: ada & gui

["Martin Dowie" <martin.dowie@baesystems.com>]

This seems like a fairly common problem - GtkAda does have a certain 'look'
on windows that isn't as clean as Claw but Claw is Windows-only.

I have toyed with creating an abstract 'GUI' library (see below) so you
could choose between GUI-implementations at compile time. Seems to work at a
_very_ small scale - could it work with more sophisticated windowing?

From this I managed to get Claw and GtkAda both creating a window (wow!).

The new Ada2005 'interface' could clean the API up quite a bit.

Any thoughts pros/cons to this sort of framework? Could it form the basis of
a 'standard' Ada GUI library?

-- Martin


-- Top level
package GUI is
   pragma Pure (Gui);

end GUI;

-- Window aspects - could be others, e.g. for fonts, etc
package GUI.Windows_Interface is
   pragma Preelaborate (GUI.Windows_Interface);

   type A_Window is abstract tagged null record;

   type A_Window_Ptr is access all A_Window'Class;

   procedure Create (Window   : out A_Window'Class;
                     Child_Of :     A_Window_Ptr := null;
                     Title    :     String       := "") is abstract;

   procedure Destroy (Window : in out A_Window'Class) is abstract;

   procedure Restore (Window : in out A_Window'Class) is abstract;

   procedure Maximise (Window : in out A_Window'Class) is abstract;

   procedure Minimise (Window : in out A_Window'Class) is abstract;

end GUI.Windows_Interface;

with GUI.Windows_Interface;


-- Applications required Windowing functions - different for each app
generic
   type Window_Type is new GUI.Windows_Interface.A_Window with private;
   type Window_Type_Ptr is access all Window_Type;
   with procedure Create (Window   : out Window_Type'Class;
                          Child_Of :     Window_Type_Ptr := null;
                          Title    :     String          := "") is <>;
   with procedure Destroy (Window : in out Window_Type'Class) is <>;
package GUI_Interface is
end GUI_Interface;