[gtkada] paint

[yoann toussaint]

  hello, I'm a beginner in gtkada and I would to make a software like 
paint with gtkada
I seek for that on the internet and it's seems to does not exist.

the first step is to draw points, line, arc on a drawing area, so I 
tried the code in gdk.drawable:

Gdkw : Gdk.Window.Gdk_Window;
    GC   : Gdk.GC.Gdk_GC;
    Font : Gdk.Font.Gdk_Font;

(first I have created a window, add a drawing area on this window)

 *procedure* Draw (Drawing : *in* *out* Gtk.Drawing_Area.Gtk_Drawing_Area) *is*
    Gdkw : Gdk.Window.Gdk_Window;
    GC   : Gdk.GC.Gdk_GC;
    Font : Gdk.Font.Gdk_Font;
    *use* *type* Glib.Gint;
 
 *begin*
    --/ Get the Gdk window/
 
    Gdkw := Gtk.Drawing_Area.Get_Window (Drawing) ;
 
    --/ Clear the window/
 
    GDK.Window.Clear (Gdkw) ;
 
    --/ Create a graphic context associated with this window/
 
    Gdk.GC.Gdk_New (GC, Gdkw);
 
    --/ Draw a line in this window/
 
    Gdk.Drawable.Draw_Line
      (Drawable => Gdkw,
       GC => GC,
       X1 =>   0, Y1 =>   0,
       X2 => 100, Y2 => 100);
 
    --/ Draw an arc/
 
    Gdk.Drawable.Draw_Arc
      (Drawable => Gdkw,
       Gc       => gc,
       Filled   => True,
       X        => 100,
       Y        => 100,
       Width    => 200,
       Height   => 100,
       Angle1   => 0 * 64,
       Angle2   => 270 * 64);
 
    --/ Ask for a given font/
 
    Gdk.Font.Load (Font,
                   "-adobe-courier-medium-i-*-*-15-*-*-*-*-*-*-*");
    Gdk.Drawable.Draw_Text
      (Drawable    => Gdkw,
       Font        => Font,
       Gc          => gc,
       X           => 50,
       Y           => 50,
       Text        => "Hello World");
    Gdk.GC.Destroy (GC);
 *end* Draw;

 so gnatmake compile the code without errors, but when I run the executable, it appears :
Gdk-CRITICAL **: file gdkwindow.c: line 929 (gdk_window_clear): assertion `window != NULL' failed.
Gdk-CRITICAL **: file gdkdraw.c: line 65 (gdk_draw_line): assertion `drawable != NULL' failed.

what 's the mistake ?

yoann toussaint