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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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The Gnome Development Framework
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<font color="#000000" size="2">GTK+ / Gnome Application
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<div class="SECT1">
<h1 class="SECT1">
<a name="Z4">The Gnome Development Framework</a>
</h1>
<p>
Gnome's application development framework centers around a
suite of libraries, all written in portable ANSI C and
intended to be used on UNIX-like systems. Libraries which
involve graphics realy on the X Window System. Wrappers are
available which export the Gnome API to nearly any language
you can think of, including Ada, Scheme, Python, Perl, Tom,
Eiffel, Dylan, and Objective C. There are at least three
different C++ wrappers as well.
</p>
<p>
This book will cover the C interface to the libraries;
however, it should be useful for users of any language
binding, since the mapping from C to your preferred
language is typically straightforward. The book covers
version 1.0 of the Gnome libraries (including the
compatible bug fix releases, such as 1.0.9---all 1.0.x
versions are compatible).
</p>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z5">Non-Gnome Libraries</a>
</h2>
<p>
Taking full advantage of the free software tradition,
Gnome didn't start from scratch. It uses several
libraries which are maintained separately from the Gnome
project. These are a part of the Gnome application
development framework, and you can count on their
presence in a Gnome environment.
</p>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z6">glib</a>
</h3>
<p>
glib is the base of the Gnome infrastructure. It's a C
utility library, providing routines to create and
manipulate common data structures. It also addresses
portability issues; for example, many systems lack the
<tt class="FUNCTION">snprintf()</tt> function, but glib
contains an implementation called <tt class="FUNCTION">
g_snprintf()</tt> which is both guaranteed to exist on
all platforms and slightly safer than <tt class=
"FUNCTION">snprintf()</tt> (it always <span class=
"STRUCTNAME">NULL</span>-terminates the target buffer).
</p>
<p>
Gnome 1.0 uses glib version 1.2 and works with any glib
in the 1.2 series (1.2.1, 1.2.2, etc.). All glib
versions beginning with 1.2 are compatible bug-fix
releases.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z7">GTK+</a>
</h3>
<p>
GTK+, or the Gimp Tool Kit, is the GUI toolkit used in
Gnome applications. GTK+ was originally written for the
Gimp (GNU Image Manipulation Program --- <a href=
"http://www.gimp.org" target="_top">
http://www.gimp.org</a>), but has become a
general-purpose library. GTK+ depends on glib.
</p>
<p>
The GTK+ package includes GDK, the Gimp Drawing Kit,
which is a simplification and abstraction of the
low-level X Window System libraries. Since GTK+ uses
GDK rather than calling X directly, a port of GDK
permits GTK+ to run on windowing systems other than X
with relatively few modifications. GTK+ and the Gimp
have already been ported to the Win32 platform in this
way.
</p>
<p>
GTK+ provides several features for Gnome applications:
</p>
<ul>
<li>
<p>
A dynamic type system.
</p>
</li>
<li>
<p>
An object system written in C, complete with
inheritance, type checking, and a signal/callback
infrastructure. The type and object systems are not
GUI-specific.
</p>
</li>
<li>
<p>
A <tt class="CLASSNAME">GtkWidget</tt> object
written using the object system, which defines the
interface GTK+'s graphical components implement.
</p>
</li>
<li>
<p>
A large collection of useful <tt class="CLASSNAME">
GtkWidget</tt> subclasses (<i class=
"FIRSTTERM">widgets</i>); this collection forms the
bulk of GTK+'s code.
</p>
</li>
</ul>
<p>
Gnome adds a number of additional widgets to the basic
GTK+ collection.
</p>
<p>
Gnome 1.0 is based on GTK+ version 1.2. All GTK+
versions beginning with 1.2 are compatible bug-fix
releases; 1.2.1, for example.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z8">ORBit</a>
</h3>
<p>
ORBit is a CORBA 2.2 ORB written in C. It was designed
to be small and fast compared to other ORBs, and
supports the C language mapping. ORBit is implemented
as a suite of libraries.
</p>
<p>
<i class="FIRSTTERM">CORBA</i>, or Common Object
Request Broker Architecture, is a specification for
Object Request Brokers, or <i class="FIRSTTERM">
ORB</i>s. An ORB is much like a dynamic linker, but it
works with objects, rather than subroutines. At
runtime, a program can request the services of a
particular object; the ORB locates the object and
creates a connection between it and the program. For
example, an email program might request an
``addressbook'' object, and use it to look up a
person's name. Unlike dynamic linking, CORBA works fine
across a network, and even allows different programming
languages and operating systems to interact with one
another. If you're familiar with DCOM on the Windows
operating system, CORBA is analagous.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z9">Imlib</a>
</h3>
<p>
Imlib ("Image Library") provides routines for loading,
saving, displaying, and scaling images in a variety of
popular formats (including GIF, JPEG, PNG, and TIFF).
It comes in two versions; an Xlib-only version, and a
GDK-based version. Gnome uses the GDK version.
</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z10">Gnome Libraries</a>
</h2>
<p>
The libraries in this section are a part of the <tt
class="APPLICATION">gnome-libs</tt> package and were
developed specifically for the Gnome Project.
</p>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z11"><tt class="APPLICATION">libgnome</tt></a>
</h3>
<p>
<tt class="APPLICATION">libgnome</tt> is a collection
of non-GUI-related routines for use by Gnome
applications. It includes code to parse configuration
files, for example. It also includes interfaces to some
external facilities, such as internationalization (via
the GNU <tt class="APPLICATION">gettext</tt> package),
argument parsing (via the <tt class="APPLICATION">
popt</tt> package), and sound (via the Enlightenment
Sound Daemon, <tt class="APPLICATION">esound</tt>). The
<tt class="APPLICATION">gnome-libs</tt> package takes
care of interacting with these external libraries, so
the programmer does not need to concern herself with
their implementation or availability.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z12"><tt class="APPLICATION">
libgnomeui</tt></a>
</h3>
<p>
<tt class="APPLICATION">libgnomeui</tt> collects
GUI-related Gnome code. It consists primarily of
widgets designed to enhance and extend GTK+. Gnome
widgets generally impose user interface policy, which
permits a more convenient API (since there is less for
the programmer to specify). It also results in
applications with more consistent interfaces, of
course.
</p>
<p>
Highlights of <tt class="APPLICATION">libgnomeui</tt>
include:
</p>
<ul>
<li>
<p>
The <tt class="CLASSNAME">GnomeApp</tt> widget,
which makes it easy to create a nice main window
for your application. It uses another widget called
<tt class="CLASSNAME">GnomeDock</tt> which enables
users to rearrange and "undock" toolbars.
</p>
</li>
<li>
<p>
The <tt class="CLASSNAME">GnomeCanvas</tt> widget
which makes it easy to write intricate,
flicker-free custom displays.
</p>
</li>
<li>
<p>
The Gnome stock pixmaps (icons for open, close,
save, and other operations).
</p>
</li>
<li>
<p>
Convenient routines for creating and using dialogs.
</p>
</li>
<li>
<p>
The <tt class="CLASSNAME">GnomePixmap</tt> widget
which is more versatile than <tt class="CLASSNAME">
GtkPixmap</tt>.
</p>
</li>
</ul>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z13"><tt class="APPLICATION">
libgnorba</tt></a>
</h3>
<p>
<tt class="APPLICATION">libgnorba</tt> provides
CORBA-related facilities, including a security
mechanism and object activation. (Object activation is
the process of obtaining a reference to an object that
implements a given interface; it can involve executing
a server program, loading a shared library module, or
asking an existing program for a new object instance.)
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z14"><tt class="APPLICATION">libzvt</tt></a>
</h3>
<p>
This small library contains a terminal widget (<tt
class="CLASSNAME">ZvtTerm</tt>) you can use in your
Gnome programs.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z15"><tt class="APPLICATION">
libart_lgpl</tt></a>
</h3>
<p>
This library contains graphics rendering routines by
Raph Levien. The routines included here are released
under the GNU Library General Public License and used
in the <tt class="CLASSNAME">GnomeCanvas</tt> widget;
Raph Levien also sells an enhanced proprietary version.
<tt class="APPLICATION">libart_lgpl</tt> provides
antialiasing, microtile refresh regions, and other
magic. In essence it is a vector graphics rasterization
library, functionally analogous to the PostScript
language.
</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z16">Other Libraries</a>
</h2>
<p>
These libraries are commonly used in Gnome applications,
but are not a part of <tt class="APPLICATION">
gnome-libs</tt> proper.
</p>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z17"><tt class="APPLICATION">
gnome-print</tt></a>
</h3>
<p>
<tt class="APPLICATION">gnome-print</tt> is still
somewhat experimental, but very promising. It uses <tt
class="APPLICATION">libart_lgpl</tt> and works nicely
with <tt class="CLASSNAME">GnomeCanvas</tt>. It
provides virtual output devices (called "print
contexts"), so a single codebase can output to a print
preview widget, to PostScript, and eventually to other
printer formats. <tt class="APPLICATION">
gnome-print</tt> also includes printing-related GUI
elements, like a print setup dialog, and a virtual font
interface (to deal with the problem that X fonts are
not printable).
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z18"><tt class="APPLICATION">
gnome-xml</tt></a>
</h3>
<p>
<tt class="APPLICATION">gnome-xml</tt> is a
non-validating XML engine written by Daniel Veillard of
the World Wide Web Consortium. It can parse XML into a
tree structure, and output a tree structure as XML.
It's useful for any application that needs to load and
save structured data; many Gnome applications use it as
a file format. This library does not depend on any of
the others, not even glib --- so it is tied to Gnome in
name only. However, you can expect most Gnome users to
have it installed, so it should not inconvenience your
users if your application uses this library.
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z19">Guile</a>
</h3>
<p>
Guile is an implementation of the Scheme programming
language in a library, so that any application can have
an embedded Scheme interpreter. It is the official
extension language of the GNU Project, and is used by
several Gnome applications. Adding an extension
language to your application might sound complex, but
Guile makes it almost trivial. (Several Gnome
applications support Perl and Python as well; it is
usually easy to support several languages once you
implement the first. But Guile has a special place in
the Gnome developer's hearts.)
</p>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z20">Bonobo</a>
</h3>
<p>
At press time, the Gnome hackers were putting the
finishing touches on Bonobo. Bonobo is a compound
document architecture in the tradition of Microsoft's
OLE; it allows you to embed charts in spreadsheets, for
example. It will be used pervasively throughout Gnome;
any application will be able to display MIME-typed data
such as plain text, HTML, or images by asking the Gnome
libraries for an appropriate Bonobo component. Look for
Bonobo technology in the next major Gnome release.
</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z21">A Word About Header Files</a>
</h2>
<p>
Throughout the book, the exact header file which declares
each function is given alongside the function prototype.
This is to facilitate your exploration of the source
code. However, you probably don't want to manually
include the hundreds of headers found in GTK+ and Gnome.
You can include all GTK+ headers <i class="EMPHASIS">en
masse</i> by including the <tt class="FILENAME">
gtk/gtk.h</tt> header file. <tt class="FILENAME">
gtk/gtk.h</tt> also includes <tt class="FILENAME">
gdk/gdk.h</tt> for you. You can include all Gnome headers
by including <tt class="FILENAME">gnome.h</tt>; <tt
class="FILENAME">gnome.h</tt> includes <tt class=
"FILENAME">gtk/gtk.h</tt> for you. Most Gnome application
files simply include <tt class="FILENAME">gnome.h</tt>.
</p>
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