gtk-tut.sgml

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<book id="gtk-tut">

<bookinfo>
    <date>January 24th, 2003</date>
    <title>GTK+ 2.0 Tutorial</title>
    <authorgroup>
      <author>
        <firstname>Tony</firstname>
        <surname>Gale</surname>
      </author>
      <author>
        <firstname>Ian</firstname>
        <surname>Main</surname>
      </author>
      <author>
	<firstname>&amp; the GTK team</firstname>
      </author>
    </authorgroup>
    <abstract>
      <para>This is a tutorial on how to use GTK (the GIMP Toolkit) through its C
            interface.</para>
    </abstract>
  </bookinfo>

<toc></toc>

<!-- ***************************************************************** -->
<chapter id="ch-TutorialDownload">
<title>Tutorial Availability</title>

<para>A copy of this tutorial in SGML and HTML is distributed with each
source code release of GTK+. For binary distributions, please check with
your vendor.</para>

<para>A copy is available online for reference at <ulink 
url="http://www.gtk.org/tutorial/">http://www.gtk.org/tutorial</ulink>.</para>

<para>A packaged verion of this tutorial is available from
<ulink url="ftp://ftp.gtk.org/pub/gtk/tutorial/">
ftp://ftp.gtk.org/pub/gtk/tutorial</ulink> which contains the tutorial in
various different formats. This
package is primary for those people wanting to have the tutorial
available for offline reference and for printing.</para>

</chapter>

<!-- ***************************************************************** -->
<chapter id="ch-Introduction">
<title>Introduction</title>

<para>GTK (GIMP Toolkit) is a library for creating graphical user
interfaces. It is licensed using the LGPL license, so you can develop
open software, free software, or even commercial non-free software
using GTK without having to spend anything for licenses or royalties.</para>

<para>It's called the GIMP toolkit because it was originally written for
developing the GNU Image Manipulation Program (GIMP), but GTK has
now been used in a large number of software projects, including the
GNU Network Object Model Environment (GNOME) project. GTK is built on
top of GDK (GIMP Drawing Kit) which is basically a wrapper around the
low-level functions for accessing the underlying windowing functions
(Xlib in the case of the X windows system), and gdk-pixbuf, a library for
client-side image manipulation.
</para>
<para>The primary authors of GTK are:</para>

<itemizedlist>
<listitem><simpara> Peter Mattis <ulink url="mailto:[e-mail]">
[e-mail]</ulink></simpara>
</listitem>
<listitem><simpara> Spencer Kimball <ulink url="mailto:[e-mail]">
[e-mail]</ulink></simpara>
</listitem>
<listitem><simpara> Josh MacDonald <ulink url="mailto:[e-mail]">
[e-mail]</ulink></simpara>
</listitem>
</itemizedlist>

<para>GTK is currently maintained by:</para>

<itemizedlist>
<listitem><simpara> Owen Taylor <ulink url="mailto:[e-mail]">
[e-mail]</ulink></simpara>
</listitem>
<listitem><simpara> Tim Janik <ulink url="mailto:[e-mail]">
[e-mail]</ulink></simpara>
</listitem>
</itemizedlist>

<para>GTK is essentially an object oriented application programmers
interface (API). Although written completely in C, it is implemented
using the idea of classes and callback functions (pointers to
functions).</para>

<para>There is also a third component called GLib which contains a few
replacements for some standard calls, as well as some additional
functions for handling linked lists, etc. The replacement functions
are used to increase GTK's portability, as some of the functions
implemented here are not available or are nonstandard on other Unixes
such as g_strerror(). Some also contain enhancements to the libc
versions, such as g_malloc() that has enhanced debugging utilities.</para>

<para>In version 2.0, GLib has picked up the type system which forms the
foundation for GTK's class hierarchy, the signal system which is used
throughout GTK, a thread API which abstracts the different native thread APIs 
of the various platforms and a facility for loading modules.
</para>

<para>As the last component, GTK uses the Pango library for internationalized
text output.
</para>

<para>This tutorial describes the C interface to GTK. There are GTK
bindings for many other languages including C++, Guile, Perl, Python,
TOM, Ada95, Objective C, Free Pascal, Eiffel, Java and C#. If you intend to
use another language's bindings to GTK, look at that binding's
documentation first. In some cases that documentation may describe
some important conventions (which you should know first) and then
refer you back to this tutorial. There are also some cross-platform
APIs (such as wxWindows and V) which use GTK as one of their target
platforms; again, consult their documentation first.</para>

<para>If you're developing your GTK application in C++, a few extra notes
are in order. There's a C++ binding to GTK called GTK--, which
provides a more C++-like interface to GTK; you should probably look
into this instead. If you don't like that approach for whatever
reason, there are two alternatives for using GTK. First, you can use
only the C subset of C++ when interfacing with GTK and then use the C
interface as described in this tutorial. Second, you can use GTK and
C++ together by declaring all callbacks as static functions in C++
classes, and again calling GTK using its C interface. If you choose
this last approach, you can include as the callback's data value a
pointer to the object to be manipulated (the so-called "this" value).
Selecting between these options is simply a matter of preference,
since in all three approaches you get C++ and GTK. None of these
approaches requires the use of a specialized preprocessor, so no
matter what you choose you can use standard C++ with GTK.</para>

<para>This tutorial is an attempt to document as much as possible of GTK,
but it is by no means complete. This tutorial assumes a good
understanding of C, and how to create C programs. It would be a great
benefit for the reader to have previous X programming experience, but
it shouldn't be necessary. If you are learning GTK as your first
widget set, please comment on how you found this tutorial, and what
you had trouble with. There are also C++, Objective C, ADA, Guile and
other language bindings available, but I don't follow these.</para>

<para>This document is a "work in progress". Please look for updates on
<ulink url="http://www.gtk.org/">http://www.gtk.org/</ulink>.</para>

<para>I would very much like to hear of any problems you have learning GTK
from this document, and would appreciate input as to how it may be
improved. Please see the section on <link linkend="ch-Contributing">Contributing
</link> for further information.</para>

</chapter>

<!-- ***************************************************************** -->
<chapter id="ch-GettingStarted">
<title>Getting Started</title>

<para>The first thing to do, of course, is download the GTK source and
install it. You can always get the latest version from <ulink 
url="ftp://ftp.gtk.org/pub/gtk">ftp.gtk.org</ulink>. You can also view 
other sources of GTK information on
<ulink url="http://www.gtk.org/">http://www.gtk.org/</ulink>. GTK
uses GNU autoconf for configuration. Once untar'd, type 
<literal>./configure --help</literal> to see a list of options.</para>

<para>The GTK source distribution also contains the complete source to all
of the examples used in this tutorial, along with Makefiles to aid
compilation.</para>

<para>To begin our introduction to GTK, we'll start with the simplest
program possible. This program will create a 200x200 pixel window and
has no way of exiting except to be killed by using the shell.</para>

<para>
<inlinemediaobject>
<imageobject>
<imagedata fileref="images/base.png" format="png">
</imageobject>
</inlinemediaobject>
</para>

<programlisting role="C">
<!-- example-start base base.c -->

#include &lt;gtk/gtk.h&gt;

int main( int   argc,
          char *argv[] )
{
    GtkWidget *window;
    
    gtk_init (&amp;argc, &amp;argv);
    
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_widget_show  (window);
    
    gtk_main ();
    
    return 0;
}
<!-- example-end -->
</programlisting>

<para>You can compile the above program with gcc using:</para>
<para><literallayout>
<literal>gcc base.c -o base `pkg-config --cflags --libs gtk+-2.0`</literal>
</literallayout></para>

<para>The meaning of the unusual compilation options is explained below in
<link linkend="sec-Compiling">Compiling Hello World</link>.</para>

<para>All programs will of course include <filename>gtk/gtk.h</filename> which 
declares the variables, functions, structures, etc. that will be used in your GTK
application.</para>

<para>The next line:</para>

<programlisting role="C">
gtk_init (&amp;argc, &amp;argv);
</programlisting>

<para>calls the function gtk_init(gint *argc, gchar ***argv) which will be called 
in all GTK applications. This sets up a few things for us such as the default visual 
and color map and then proceeds to call gdk_init(gint *argc, gchar ***argv). 
This function initializes the library for use, sets up default signal handlers, and 
checks the arguments passed to your application on the command line, looking for
one of the following:</para>

<itemizedlist spacing=Compact>
<listitem><simpara> <literal>--gtk-module</literal></simpara>
</listitem>
<listitem><simpara> <literal>--g-fatal-warnings</literal></simpara>
</listitem>
<listitem><simpara> <literal>--gtk-debug</literal></simpara>
</listitem>
<listitem><simpara> <literal>--gtk-no-debug</literal></simpara>
</listitem>
<listitem><simpara> <literal>--gdk-debug</literal></simpara>
</listitem>
<listitem><simpara> <literal>--gdk-no-debug</literal></simpara>
</listitem>
<listitem><simpara> <literal>--display</literal></simpara>
</listitem>
<listitem><simpara> <literal>--sync</literal></simpara>
</listitem>
<listitem><simpara> <literal>--name</literal></simpara>
</listitem>
<listitem><simpara> <literal>--class</literal></simpara>
</listitem>
</itemizedlist>

<para>It removes these from the argument list, leaving anything it does not
recognize for your application to parse or ignore. This creates a set
of standard arguments accepted by all GTK applications.</para>

<para>The next two lines of code create and display a window.</para>

<programlisting role="C">
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_widget_show (window);
</programlisting>

<para>The <literal>GTK_WINDOW_TOPLEVEL</literal> argument specifies that we want the
window to undergo window manager decoration and placement. Rather than
create a window of 0x0 size, a window without children is set to
200x200 by default so you can still manipulate it.</para>

<para>The gtk_widget_show() function lets GTK know that we are done setting
the attributes of this widget, and that it can display it.</para>

<para>The last line enters the GTK main processing loop.</para>

<programlisting role="C">
  gtk_main ();
</programlisting>

<para>gtk_main() is another call you will see in every GTK application.
When control reaches this point, GTK will sleep waiting for X events
(such as button or key presses), timeouts, or file IO notifications to
occur. In our simple example, however, events are ignored.</para>

<!-- ----------------------------------------------------------------- -->
<sect1 id="sec-HelloWorld">
<title>Hello World in GTK</title>

<para>Now for a program with a widget (a button). It's the classic
hello world a la GTK.</para>

<para>
<inlinemediaobject>
<imageobject>
<imagedata fileref="images/helloworld.png" format="png">
</imageobject>
</inlinemediaobject>
</para>

<programlisting role="C">
<!-- example-start helloworld helloworld.c -->

#include &lt;gtk/gtk.h&gt;

/* This is a callback function. The data arguments are ignored
 * in this example. More on callbacks below. */
static void hello( GtkWidget *widget,
                   gpointer   data )
{
    g_print ("Hello World\n");
}

static gboolean delete_event( GtkWidget *widget,
                              GdkEvent  *event,
                              gpointer   data )
{
    /* If you return FALSE in the "delete_event" signal handler,
     * GTK will emit the "destroy" signal. Returning TRUE means
     * you don't want the window to be destroyed.
     * This is useful for popping up 'are you sure you want to quit?'
     * type dialogs. */

    g_print ("delete event occurred\n");

    /* Change TRUE to FALSE and the main window will be destroyed with
     * a "delete_event". */

    return TRUE;
}

/* Another callback */
static void destroy( GtkWidget *widget,
                     gpointer   data )
{
    gtk_main_quit ();
}

int main( int   argc,
          char *argv[] )
{
    /* GtkWidget is the storage type for widgets */
    GtkWidget *window;
    GtkWidget *button;