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