From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!newsfeed0.kamp.net!newsfeed.kamp.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Where do I get my Cairo context from (in GTK3)?
Date: Sun, 24 Apr 2016 22:44:23 +0200
Message-ID: <do4ph6Fa6ghU1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: individual.net W5w9Tr32O73HU7Zlm21OfwBmMB5bflbY9+W+JUOi2AqqaTtKza
Cancel-Lock: sha1:emKYtDoXZiwK/iicc1u1zDfk1cE=
X-Mozilla-News-Host: news://News.Individual.DE:119
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.6.0
Xref: news.eternal-september.org comp.lang.ada:30269
Date: 2016-04-24T22:44:23+02:00
List-Id: <comp.lang.ada>

In GTk2 you got it from a call of Gdk.Cairo.Create.

In GTK3 it is passed as a parameter of the callback function for the 
"draw" signal with the C prototype:

    gboolean
    user_function (GtkWidget    *widget,
                   CairoContext *cr,
                   gpointer      user_data)

So I wrote in my Ada program (GNAT, gtkada):

    package DA_Ret_Callback is new Gtk.Handlers.User_Return_Callback
      (Gtk.Widget.Gtk_Widget_Record, Boolean, Handler_DataD);


    function Draw_Handler
      (da: access Gtk.Widget.Gtk_Widget_Record'Class;
       cc: Cairo.Cairo_Context;
       hd: Handler_DataD) return Boolean is
    begin
       ...
    end Draw_Handler;


    procedure Connect_Handlers
      (obj: Glib.Object.GObject; hd: Handler_DataD;
       sn_realize, sn_config, sn_draw: Glib.Signal_Name) is
    begin
       ...
       DA_Ret_Callback.Connect
	(Gtk.Widget.Gtk_Widget(obj), sn_draw,
	 DA_Ret_Callback.To_Marshaller(Draw_Handler'Access),
	 hd);
    end Connect_Handlers;


The compiler then tells me

    gui-canvas.adb:79:25: no candidate interpretations match the actuals:
    gui-canvas.adb:79:52: expected type "Handler" defined at
    gtk-marshallers.ads:309, instance at gtk-handlers.ads:468,
    instance at line 20

That means that he expects a handler

          type Handler is access function
	           (Widget    : access Widget_Type'Class;
	            User_Data : User_Type) return Return_Type;
	
So where do I get the cairo context from?
-- 
Frank Hrebabetzky		+49 / 6355 / 989 5070