Running Linux, 5th Edition - Matthias Kalle Dalheimer [406]
Qt , a C++ GUI toolkit written by the Norwegian company Trolltech, is an excellent package for GUI development in C++. It sports an ingenious mechanism for connecting user interaction with program code, a very fast drawing engine, and a comprehensive but easy-to-use API. Qt is considered by many as the de facto GUI programming standard because it is the foundation of the KDE desktop (see "The K Desktop Environment" in Chapter 3), which is the most prominent desktop on today's Linux systems.
Qt is a commercial product, but it is also released under the GPL, meaning that you can use it for free if you write software for Unix (and hence Linux) that is licensed under the GPL as well. In addition, (commercial) Windows and Mac OS X versions of Qt are available, which makes it possible to develop for Linux, Windows, and Mac OS X at the same time and create an application for another platform by simply recompiling. Imagine being able to develop on your favorite Linux operating system and still being able to target the larger Windows market! One of the authors, Kalle, uses Qt to write both free software (the KDE just mentioned) and commercial software (often cross-platform products that are developed for Linux, Windows, and Mac OS X). Qt is being very actively developed; for more information, see Programming with Qt (O'Reilly).
Another exciting recent addition to Qt is that it can run on embedded systems, without the need for an X server. And which operating system would it support on embedded systems if not Embedded Linux? Many embedded devices with graphical screens already run Embedded Linux and Qt/Embedded — for example, some cellular telephones, car computers, medical devices, and many more. It won't say "Linux" in large letters on the box, but that's what is inside!
Qt also comes with a GUI builder called Qt Designer that greatly facilitates the creation of GUI applications. It is included in the GPL version of Qt as well, so if you download Qt (or simply install it from your distribution CDs), you have the Designer right away. Finally, Python bindings for Qt let you employ its attractive and flexible interface without having to learn a low-level language.
For those who do not like to program in C++, GTK might be a good choice. GTK was originally written for the image manipulation program GIMP. GTK programs usually offer response times that are just as good as those of Qt programs, but the toolkit is not as complete. Documentation is especially lacking. For C-based projects, though, GTK is a good alternative if you do not need to be able to recompile your code on Windows. A Windows port has been developed as well. Good C++ bindings have also been created, so more and more GTK developers are choosing to develop their software in C++ instead of in C.
Many programmers are finding that building a user interface, even with a complete set of widgets and routines in C, requires much overhead and can be quite difficult. This is a question of flexibility versus ease of programming: the easier the interface is to build, the less control the programmer has over it. Many programmers are finding that prebuilt widgets are adequate for their needs, so the loss in flexibility is not a problem.
One of the most popular toolkits in the 1980s and 1990s was the commercial Motif library and widget set, available from several vendors for an inexpensive single-user license fee. Many applications are available that utilize Motif. Binaries statically linked with Motif may be distributed freely and used by people who don't own Motif.
Motif seems to be in use mostly for legacy projects; most programmers have moved on to the newer Qt or GTK toolkits. However, Motif is still being actively developed (albeit rather slowly). It also has some problems. First, programming with Motif can be frustrating. It is difficult, error-prone,