Qt toolkit
In computer programming, the Qt toolkit is a cross-platform graphical widget toolkit for the development of GUI programs. Qt is most notably used in the KDE desktop environment. It is produced by the Norwegian company Trolltech, formerly Quasar Technologies.
Qt uses an extended version of the C++ programming language, but bindings exist for Python, C and Perl. It runs on all major platforms, and has extensive internationalization support. Non-GUI features include SQL database access, XML parsing, and a unified cross-platform API for file handling.
Varieties
Four varieties of Qt now exist, supporting various platforms, but with varying licenses:
- Qt/X11 — Qt for X Window System (GPL or proprietary)
- Qt/Mac — Qt for Apple Mac OS X (formerly proprietary only, now also under GPL)
- Qt/Windows — Qt for Microsoft Windows (proprietary, though an obsolete version is available under a free license)
- Qt/Embedded — designed for PDAs and Embedded Linux (GPL)
The KDE on Cygwin project is also working on a new native Windows version of Qt, based entirely on the Qt/X11 source code, licensed under the GPL.
Current
Trolltech is currently developing QSA — Qt Script for Applications. QSA will let Qt developers make their applications scriptable. QSA is based on ECMAScript (a.k.a. JavaScript).
History
Quasar Technologies began development of the "Quasar Toolkit" in 1992, two years before Quasar changed its name to Trolltech and the name of the toolkit to "Qt".
Controversy erupted around 1997 when it became clear that KDE was going to become one of the leading desktop environments for GNU/Linux. As KDE was based on Qt, many people in the open source and free software movements were worried that an essential piece of one of their major operating systems would be under commercial control.
This gave rise to two efforts: the Harmony toolkit which sought to duplicate the Qt Toolkit under a free software license and the GNOME desktop that was meant to supplant KDE entirely. The GNOME Desktop uses the Gtk+ toolkit which was written for the GIMP, and mainly uses the C programming language. Gtk+ endeavors to have the same cross-platform capabilities as Qt.
Trolltech licensed Qt under the Q Public License (QPL), a free software license, but one regarded by the FSF as incompatible with the GPL. Compromises were sought between KDE and Trolltech wherein Qt would not be able to fall under a more restrictive license than the QPL, even if Trolltech was bought out or went bankrupt. On September 4, 2000, Trolltech announced that the upcoming Qt 2.2 release would be licensed under the GPL. Qt 2.2 was released on September 6, 2000, with KDE 2.0 following on October 23, 2000. Subsequent releases of Qt/X11 have also been released under the GPL. The current version is 3.3. A technology preview of Qt 4 has recently been released
