162 lines
10 KiB
HTML
162 lines
10 KiB
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<META NAME="CREATED" CONTENT="20041114;15091400">
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<BODY LANG="de-DE" DIR="LTR">
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<H1 ALIGN=CENTER>Whitepaper: wxWidgets on the GNOME desktop</H1>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Introduction</FONT></FONT></P>
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<P>wxWidgets<A HREF="http://www.wxwidgets.org/"><SUP>[1]</SUP></A>
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(formely known as wxWindows) is a C++ cross-platform GUI library,
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whose distintive feature is the use of native calls and native
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widgets on the respective platform, i.e. an application compiled for
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the Linux platform will use the GTK+<A HREF="http://www.gtk.org/"><SUP>[2]</SUP></A>
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library for displaying the various widgets. There is also a version
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(„port“) of wxWidgets which uses the Motif toolkit for
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displaying its widgets (this port is commonly referred to as wxMotif)
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and another one, which only uses X11 calls and which draws its
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widgets entirely itself, without using any outside library. This port
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is called wxX11 or sometimes more generally wxUniv (short for
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wxUniversal), since this widget set (implemented entirely within
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wxWidgets) is available wherever wxWidgets is available. Since this
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short overview is mainly about how to write wxWidgets applications
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for the GNOME<A HREF="http://www.gnome.org/"><SUP>[3]</SUP></A>
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desktop, I will focus on the GTK+ port, which is generally referred
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to as wxGTK.
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</P>
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<P>wxGTK still supports the old version GTK+ 1.2, but it now defaults
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to the uptodate version GTK+ 2.X, which is the basis for the current
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GNOME desktop. By way of using GTK+ 2.X and its underlying text
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rendering library Pango<A HREF="http://www.pango.org/"><SUP>[4]</SUP></A>,
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wxGTK fully supports the Unicode character set and it can render text
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in any language and script, that is supported by Pango.</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>wxWidgets'
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design principles sofar</FONT></FONT></P>
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<P>The three main design goals of the wxWidgets library are
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portability across the supported platforms, complete integration with
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the supported platforms and a broad range of functionality covering
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most aspects of GUI and non-GUI application programming. Sometimes,
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various aspects of these design goals contradict each other and this
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holds true especially for the Linux platform which – from the
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point of view of the desktop environment integration – is
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lagging behind the other two major desktops (Windows and OS X)
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mostly because of the schism between the GTK+ based GNOME desktop and
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the Qt<A HREF="http://www.trolltech.com/"><SUP>[5]</SUP></A> based
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KDE<A HREF="http://www.kde.org/"><SUP>[6]</SUP></A> desktop. So far,
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the typical wxWidgets user targeted Windows, maybe OS X and Linux
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<I>in general</I>, so the aim was to make wxGTK applications run as
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well as possible on as many versions of Linux as possible, including
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those using the KDE environment. Luckily, most of these distributions
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included the GTK+ library (for running applications like the GIMP,
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GAIM, Evolution or Mozilla) whereas the GNOME libraries were not
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always installed by default. Also, the GNOME libraries didn't really
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offer substantial value so that the hassle of installing them was
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hardly justified. Therefore, much effort was spent on making wxGTK
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fully functional without relying on the GNOME libraries, mostly by
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reimplementing as much as sensible of the missing functionality. This
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included a usable file selection dialog, a printing system for
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PostScript output, code for querying MIME-types and file-icon
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associations, classes for storing application preferences and
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configurations, the possibility to display mini-apps in the taskbar,
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a full-featured HTML based help system etc. With all that in place
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you can write a pretty fully featured wxWidgets application on an
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old Linux system with little more installed than X11 and GTK+.</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Recent
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developments</FONT></FONT></P>
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<P>Recently, several key issues have been addressed by the GNOME
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project. Sometimes integrated into the newest GTK+ releases (such as
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the file selecter), sometimes as part of the GNOME libraries (such as
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the new printing system with Pango integration or the mime-types
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handling in gnome-vfs), sometimes as outside projects (such as the
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media/video backend based on the Gstreamer<A HREF="http://gstreamer.freedesktop.org/"><SUP>[7]</SUP></A>
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project). Also, care has been taken to unify the look and feel of
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GNOME applications by writing down a number of rules (modestly called
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„Human Interface Guidelines“<A HREF="http://developer.gnome.org/projects/gup/hig"><SUP>[8]</SUP></A>)
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and more and more decisions are taken in a desktop neutral way (for
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both GNOME and KDE), mostly as part of the FreeDesktop<A HREF="http://www.freedesktop.org/"><SUP>[9]</SUP></A>
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initiative. This development together with the rising number of
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OpenSource projects using wxWidgets mainly for the Linux and more
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specifically GNOME desktop has led to a change of direction within
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the wxWidgets project, now working on making more use of GNOME
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features when present. The general idea is to call the various GNOME
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libraries if they are present and to offer a reasonable fallback if
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not. I'll detail on the various methods chosen below:</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Printing
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system</FONT></FONT></P>
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<P>The old printing system ....</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>MIME-type
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handling</FONT></FONT></P>
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<P>The old mime-type system used to simply query some files stored in
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„typical“ locations for the respective desktop
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environment. Since both the format and the location of these files
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changed rather frequently, this system was never fully working as
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desired for reading the MIME-types and it never worked at all for
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writing MIME-types or icon/file associations. ...</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>The
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new file dialog</FONT></FONT></P>
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<P>Previously, wxGTK application made use of a file dialog written in
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wxWidgets itself, since the default GTK+ file dialog was simplistic
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to say the least. This has changed with version GTK+ 2.4, where a
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nice and powerful dialog has been added. wxGTK is using it now.</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>File
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configuration and preferences</FONT></FONT></P>
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<P>The usual Unix way of saving file configuration and preferences is
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to write and read a so called „dot-file“, basically a
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text file in a user's home directory starting with a dot. This was
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deemed insufficient by the GNOME desktop project and therefore they
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introduced the so called GConf system, for storing and retrieving
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application and sessions information....</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Results
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and discussion</FONT></FONT></P>
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<P>One of wxWidgets' greatest merits is the ability to write an
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application that not only runs on different operating systems but
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especially under Linux even on rather old systems with only a minimal
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set of libraries installed – using a single application binary.
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This was possible since most of the relevant functionality was either
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located in the only required library (GTK+) or was implemented within
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wxWidgets. Recent development outside the actual GTK+ project has
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made it necessary to rethink this design and make use of other
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projects' features in order to stay uptodate with current
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techological trends. Therefore, a system was implemented within
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wxWidgets that queries the system at runtime about various libraries
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and makes use of their features whenever possible, but falls back to
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a reasonable solution if not. The result is that you can create and
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distribute application binaries that run on old Linux systems and
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integrate fully with modern desktops, if they are available. This is
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not currently possible with any other software.</P>
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<P>Copyright 2004 © Robert Roebling, MD. No reprint permitted
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without written prior authorisation.<BR>Last modified 14/11/04</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>About
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the author</FONT></FONT></P>
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<P>Robert Roebling works as a medical doctor in the Department of
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Neurology at the University clinic of Ulm in Germany. He has studied
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Computer Sciences for a few semesters and is involved in the
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wxWidgets projects since about 1996. He has started and written most
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of wxGTK port (beginning with GTK+ around 0.9) and has contributed to
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quite a number projects within wxWidgets, ranging from the image
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classes to Unicode support to making both the Windows and the GTK+
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ports work on embedded platform (mostly PDAs). He is happily married,
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has two children and never has time.</P>
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<P STYLE="margin-top: 0.42cm; page-break-after: avoid"><FONT FACE="Albany, sans-serif"><FONT SIZE=4>Links
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and citations</FONT></FONT></P>
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<P>[1] See the wxWidgets homepage at <A HREF="http://www.wxwidgets.org/">www.wxwidgets.org</A>.<BR>[2]
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See the GTK+ homepage at <A HREF="http://www.gtk.org/">www.gtk.org</A>.<BR>[3]
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See more about GNOME at <A HREF="http://www.gnome.org/">www.gnome.org</A>,
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<A HREF="http://www.gnomedesktop.org/">www.gnomedesktop.org</A>,
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<A HREF="http://www.gnomejournal.org/">www.gnomejournal.org</A>,
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<A HREF="http://www.gnomefiles.org/">www.gnomefiles.org</A>.<BR>[4]
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See the Pango homepage at <A HREF="http://www.pango.org/">www.pango.org</A>.<BR>[5]
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See the Qt homepage at <A HREF="http://www.trolltech.com/">www.trolltech.com</A>.<BR>[6]
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See the KDE homepage at <A HREF="http://www.kde.org/">www.kde.org</A>.<BR>[7]
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See Gstreamer homepage at <A HREF="http://gstreamer.freedesktop.org/">gstreamer.freedesktop.org</A>.<BR>[8]
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See GNOME's Human Interface Guidelines at
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<A HREF="http://developer.gnome.org/projects/gup/hig">developer.gnome.org/projects/gup/hig</A>.<BR>[9]
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See FreeDesktop's homepage at <A HREF="http://www.freedesktop.org/">www.freedesktop.org</A>.<BR><BR><BR>
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</P>
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