Date: Sat, 10 Sep 2005 14:48:38 -0300
From: romildo at uber.com.br
To: lablgtk at math.nagoya-u.ac.jp
Subject: Wrapping a new widget
Message-ID: <20050910174838.GA16269 at malaquias>
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Hi.

I want to learn how to wrap a new widget from a C
library. For that I am working with the gtk+extra
library (http://gtkextra.sourceforge.net/).

To start with, I am wrapping just the constructor
of the widget GtkPlotCanvas. The programs
needed are attached.

When compiling the test program with compiler
option -i, we can see the infered types of the
values:

$ ocamlc -i lablgtk.cma gtkInit.cmo gExtra.cmo lablgtkextra.cma test-extra.ml -o test-extra
File "test-extra.ml", line 10, characters 2-50:
Warning: this expression should have type unit.
val window : GWindow.window
val canvas : GObj.widget
val main : unit -> unit

I was expecting the type of canvas to be GExtra.plot_canvas
instead of GObj.widget. Please, help me to change
this program so that this is the case.

Romildo

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/* ml_gtkextra.c */

#include <gtkextra/gtkextra.h>

#include <caml/mlvalues.h>
#include <caml/alloc.h>
#include <caml/memory.h>
#include <caml/callback.h>
#include <caml/fail.h>

#include "wrappers.h"
#include "ml_glib.h"
#include "ml_gobject.h"
#include "ml_gdk.h"
#include "ml_gtk.h"

#include "gtk_tags.h"

CAMLprim value ml_gtkextra_init(value unit)
{
    GType t =
       gtk_plot_canvas_get_type ();
    return Val_GType(t);
}

#define GtkPlotCanvas_val(val) check_cast(GTK_PLOT_CANVAS,val)

ML_3 (gtk_plot_canvas_new, Int_val, Int_val, Double_val, Val_GtkWidget_sink)

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(* gtkExtra.ml *)

open Gaux
open Gobject
open Gtk
open Tags
open GtkBase

external _gtkextra_init : unit -> unit = "ml_gtkextra_init"
let () = _gtkextra_init ()

type plot_canvas = [Gtk.widget|`plot_canvas]

module PlotCanvas = struct
  external new_plot_canvas : int -> int -> float -> plot_canvas Gobject.obj = "ml_gtk_plot_canvas_new"
end

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(* gExtra.ml *)

open StdLabels
open Gaux
open Gobject
open Gtk
open GtkBase
open GtkExtra
open GObj

class plot_canvas obj = object
  inherit GObj.widget (obj : GtkExtra.plot_canvas Gtk.obj)
end

let plot_canvas width heigth magnification ?packing ?show () =
  let w = PlotCanvas.new_plot_canvas width heigth magnification in
    GObj.pack_return (new plot_canvas w) ~packing ~show

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