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Robert Roebling 66266922ca The wxGNOME whitepaper-to-be. 
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30523 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
2004-11-14 21:52:55 +00:00

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<H1 ALIGN=CENTER>Whitepaper: wxWidgets on the GNOME desktop</H1>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Introduction</FONT></FONT></P>
<P>wxWidgets<A HREF="http://www.wxwidgets.org/"><SUP>[1]</SUP></A>
(formely known as wxWindows) is a C++ cross-platform GUI library,
whose distintive feature is the use of native calls and native
widgets on the respective platform, i.e. an application compiled for
the Linux platform will use the GTK+<A HREF="http://www.gtk.org/"><SUP>[2]</SUP></A>
library for displaying the various widgets. There is also a version
(&bdquo;port&ldquo;) of wxWidgets which uses the Motif toolkit for
displaying its widgets (this port is commonly referred to as wxMotif)
and another one, which only uses X11 calls and which draws its
widgets entirely itself, without using any outside library. This port
is called wxX11 or sometimes more generally wxUniv (short for
wxUniversal), since this widget set (implemented entirely within
wxWidgets) is available whereever wxWidgets is available. Since this
short overview is mainly about how to write wxWidgets applications
for the GNOME<A HREF="http://www.gnome.org/"><SUP>[3]</SUP></A>
desktop, I will focus on the GTK+ port, which is generally referred
to as wxGTK.
</P>
<P>wxGTK still supports the old version GTK+ 1.2, but it now defaults
to the uptodate version GTK+ 2.X, which is the basis for the current
GNOME desktop. By way of using GTK+ 2.X and its underlying text
rendering library Pango<A HREF="http://www.pango.org/"><SUP>[4]</SUP></A>,
wxGTK fully supports the Unicode character set and it can render text
in any language and script, that is supported by Pango.</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>wxWidgets'
design principles sofar</FONT></FONT></P>
<P>The three main design goals of the wxWidgets library are
portability across the supported platforms, complete integration with
the supported platforms and a broad range of functionality covering
most aspects of GUI and non-GUI application programming. Sometimes,
various aspects of these design goals contradict each other and this
holds true especially for the Linux platform which &ndash; from the
point of view of the desktop environment integration &ndash; is
lagging behind the other two major desktops (Windows and MacOS X)
mostly because of the schism between the GTK+ based GNOME desktop and
the Qt<A HREF="http://www.trolltech.com/"><SUP>[5]</SUP></A> based
KDE<A HREF="http://www.kde.org/"><SUP>[6]</SUP></A> desktop. So far,
the typical wxWidgets user targeted Windows, maybe MacOS X and Linux
<I>in general</I>, so the aim was to make wxGTK applications run as
well as possible on as many versions of Linux as possible, including
those using the KDE environment. Luckily, most of these distributions
included the GTK+ library (for running applications like the GIMP,
GAIM, Evolution or Mozilla) whereas the GNOME libraries were not
always installed by default. Also, the GNOME libraries didn't really
offer substantial value so that the hassle of installing them was
hardly justified. Therefore, much effort was spent on making wxGTK
fully functional without relying on the GNOME libraries, mostly by
reimplementing as much as sensible of the missing functionality. This
included a usable file selection dialog, a printing system for
PostScript output, code for querying MIME-types and file-icon
associations, classes for storing application preferences and
configurations, the possibility to display mini-apps in the taskbar,
a full-featured HTML based help system etc. With all that in place
you can write a pretty fully featured wxWidgets application on an
old Linux system with little more installed than X11 and GTK+.</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Recent
developments</FONT></FONT></P>
<P>Recently, several key issues have been addressed by the GNOME
project. Sometimes integrated into the newest GTK+ releases (such as
the file selecter), sometimes as part of the GNOME libraries (such as
the new printing system with Pango integration or the mime-types
handling in gnome-vfs), sometimes as outside projects (such as the
media/video backend based on the Gstreamer<A HREF="http://gstreamer.freedesktop.org/"><SUP>[7]</SUP></A>
project). Also, care has been taken to unify the look and feel of
GNOME applications by writing down a number of rules (modestly called
&bdquo;Human Interface Guidelines&ldquo;<A HREF="http://developer.gnome.org/projects/gup/hig"><SUP>[8]</SUP></A>)
and more and more decisions are taken in a desktop neutral way (for
both GNOME and KDE), mostly as part of the FreeDesktop<A HREF="http://www.freedesktop.org/"><SUP>[9]</SUP></A>
initiative. This development together with the rising number of
OpenSource projects using wxWidgets mainly for the Linux and more
specifically GNOME desktop has led to a change of direction within
the wxWidgets project, now working on making more use of GNOME
features when present. The general idea is to call the various GNOME
libraries if they are present and to offer a reasonable fallback if
not. I'll detail on the various methods chosen below:</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Printing
system</FONT></FONT></P>
<P>The old printing system ....</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>MIME-type
handling</FONT></FONT></P>
<P>The old mime-type system used to simply query some files stored in
&bdquo;typical&ldquo; locations for the respective desktop
environment. Since both the format and the location of these files
changed rather frequently, this system was never fully working as
desired for reading the MIME-types and it never worked at all for
writing MIME-types or icon/file associations. ...</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>The
new file dialog</FONT></FONT></P>
<P>Previously, wxGTK application made use of a file dialog written in
wxWidgets itself, since the default GTK+ file dialog was simplistic
to say the least. This has changed with version GTK+ 2.4, where a
nice and powerful dialog has been added. We now query the GTK+
library, if the new file dialog functions are available and wxGTK
applications will show and use them if that is the case, otherwise,
they will fall back to the old generic one.</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>File
configuration and preferences</FONT></FONT></P>
<P>The usual Unix way of saving file configuration and preferences is
to write and read a so called &bdquo;dot-file&ldquo;, basically a
text file in a user's home directory starting with a dot. This was
deemed insufficient by the GNOME desktop project and therefore they
introduced the so called GConf system, for storing and retrieving
application and sessions information....</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Results
and discussion</FONT></FONT></P>
<P>One of wxWidgets' greatest merits is the ability to write an
application that not only runs on different operating systems but
especially under Linux even on rather old systems with only a minimal
set of libraries installed &ndash; using a single application binary.
This was possible since most of the relevant functionality was either
located in the only required library (GTK+) or was implemented within
wxWidgets. Recent development outside the actual GTK+ project has
made it necessary to rethink this design and make use of other
projects' features in order to stay uptodate with current
techological trends. Therefore, a system was implemented within
wxWidgets that queries the system at runtime about various libraries
and makes use of their features whenever possible, but falls back to
a reasonable solution if not. The result is that you can create and
distribute application binaries that run on old Linux systems and
integrate fully with modern desktops, if they are available. This is
not currently possible with any other software.</P>
<P>Copyright 2004 &copy; Robert Roebling, MD. No reprint permitted
without written prior authorisation.<BR>Last modified 14/11/04</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>About
the author</FONT></FONT></P>
<P>Robert Roebling works as a medical doctor in the Department of
Neurology at the University clinic of Ulm in Germany. He has studied
Computer Sciences for a few semesters and is involved in the
wxWidgets projects since about 1996. He has started and written most
of wxGTK port (beginning with GTK+ around 0.9) and has contributed to
quite a number projects within wxWidgets, ranging from the image
classes to Unicode support to making both the Windows and the GTK+
ports work on embedded platform (mostly PDAs). He is happily married,
has two children and never has time.</P>
<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Links
and citations</FONT></FONT></P>
<P>[1] See the wxWidgets homepage at <A HREF="http://www.wxwidgets.org/">www.wxwidgets.org</A>.<BR>[2]
See the GTK+ homepage at <A HREF="http://www.gtk.org/">www.gtk.org</A>.<BR>[3]
See more about GNOME at <A HREF="http://www.gnome.org/">www.gnome.org</A>,
<A HREF="http://www.gnomedesktop.org/">www.gnomedesktop.org</A>,
<A HREF="http://www.gnomejournal.org/">www.gnomejournal.org</A>,
<A HREF="http://www.gnomefiles.org/">www.gnomefiles.org</A>.<BR>[4]
See the Pango homepage at <A HREF="http://www.pango.org/">www.pango.org</A>.<BR>[5]
See the Qt homepage at <A HREF="http://www.trolltech.com/">www.trolltech.com</A>.<BR>[6]
See the KDE homepage at <A HREF="http://www.kde.org/">www.kde.org</A>.<BR>[7]
See Gstreamer homepage at <A HREF="http://gstreamer.freedesktop.org/">gstreamer.freedesktop.org</A>.<BR>[8]
See GNOME's Human Interface Guidelines at
<A HREF="http://developer.gnome.org/projects/gup/hig">developer.gnome.org/projects/gup/hig</A>.<BR>[9]
See FreeDesktop's homepage at <A HREF="http://www.freedesktop.org/">www.freedesktop.org</A>.<BR><BR><BR>
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