Where do I get my Cairo context from (in GTK3)?

[hreba <f_hreba@yahoo.com.br>]

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