is a
Cross-platform application development framework, widely used for the development of
GUI programs and also used for developing non-GUI programs such as console tools and servers. Qt is most notably used in
KDE , the web browser
Opera ,
Google Earth ,
Skype ,
Qtopia and
OPIE . It is produced by the
Norwegian company
Trolltech , formerly Quasar Technologies. Trolltech insiders pronounce Qt as "cute"
Interview with Trolltech president Eirik Eng on dot.kde.org.
Qt uses non-standard support. Non-GUI features include
SQL database access,
XML parsing,
Thread management, and a unified cross-platform
API for file handling.
Qt is released by Trolltech on the following ''platforms'':
There are four ''editions'' of Qt available on each of these platforms, namely:
- — edition for ''non-GUI'' development.
- — entry level GUI edition, stripped of network and database support.
- — complete edition.
- — complete edition, with some exceptionsThe ActiveQt class for ActiveX on Windows, for example, is not available in the Open Source Edition, for Free Software / Open Source developers.
Since version 4, Qt has been available under a
Dual License , the
GPL and a proprietary commercial license on all supported platforms including Windows. The commercial license allows the final application to be licensed under various
Free Software /
Open Source licenses such as the
LGPL or the
Artistic License , or a
Proprietary Software License .
Proprietary commercial development requires the commercial license, and, unlike some
Open Source software libraries, Qt is not licensed under the
GNU Lesser General Public License and does not include a
GPL Linking Exception .
All editions support a wide range of compilers, including the
GCC C++ compiler. Official support for the
Visual Studio suite
is, however, restricted to the proprietary Qt/Windows edition. The [http://sourceforge.net/projects/qtwin/ Q../Free project has released several patches [http://sourceforge.net/project/showfiles.php?group_id=49109] which add support for Microsoft Visual Studio and Borland C++ Builder to the free software/open source version of Qt/Windows.
Trolltech released Qt 4 on
June 28 ,
2005 and introduced five new technologies in the framework:
- '' A set of template container classes.
- '' A model/view architecture for item views.
- '' A 2D painting framework.
- '' A Unicode text renderer with a public API for performing low-level text layout.
- '' A modern action-based main window, toolbar, menu, and docking architecture.
Qt 4.1, released on
December 19 ,
2005 , introduced integrated
SVG Tiny support, a
PDF backend to Qt's printing system, and
a few other features .
Qt 4.2, released on
October 4 ,
2006 , introduced
Windows Vista support, introduced native CSS support for widget styling, as well as the QGraphicsView framework for efficient rendering of thousands of 2D objects onscreen, to replace Qt 3.x's QCanvas class.
Qt 4.3, released on
May 30 ,
2007 , improved
Windows Vista support, improved
OpenGL engine,
SVG file generation
{Link without Title} .
Haavard Nord and
Eirik Chambe-Eng (the original developers of Qt and the CEO and President of Trolltech respectively) began development of "Qt" in
1991 , three years before the company was incorporated as Quasar Technologies, then changed the name to Troll Tech, and then to Trolltech.
The toolkit was called Qt because the letter
Q looked beautiful in Haavard's
Emacs font, and T was inspired by
Xt , the X toolkit.
Controversy erupted around
1998 when it became clear that KDE was going to become one of the leading
Desktop Environment s for
Linux . As KDE was based on Qt, many people in the
Free Software Movement worried that an essential piece of one of their major operating systems would be proprietary.
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, which intended to supplant KDE entirely. The GNOME Desktop uses the
GTK+ toolkit, which was originally written for the
GIMP , and primarily uses the
C Programming Language .
Until version 1.45, source code for Qt was released under the should no free software/open source version of Qt be released during 12 months.
The first two versions of Qt had only two flavours: Qt/X11 for Unix and Qt/Windows for the Windows platform. The Windows platform was only available under the proprietary license which meant free/open source applications written in Qt for X11 could not be ported to Windows without purchasing the QPL edition. In the end of 2001, Trolltech released Qt 3.0 which added support for the Mac OS X platform. The Mac OS X support was available only in the proprietary license, until June 2003, where Trolltech released Qt 3.2 with Mac OS X support available under the GPL.
In 2002 members of the
KDE On Cygwin project began porting the GPL licensed Qt/X11 code base to Windows
This was in response to Trolltech's refusal to license Qt/Windows under the GPL on the grounds that Windows was not a free software/open source platform [http://lists.kde.org/?l=kde-cygwin&m=104431728920022&w=2 [http://web.archive.org/web/20031005175911/http://www.trolltech.com/developer/faqs/noncomm.html]. The project achieved reasonable success although it never reached production quality.
This was resolved when Trolltech released Qt/Windows 4 under the GPL in June 2005. Qt 4 now supports the same set of platforms in the free software/open source editions as in the proprietary edition, so it is now possible to create GPL-licensed free/open source applications using Qt on all supported platforms.
The innovation of Qt when it was first released relied on a few key concepts.
Qt uses its own paint engine and controls. This makes the work of porting to other platforms easier because very few classes in Qt depended on the target platform. Qt used to emulate the native look of its intended platforms, which occasionally led to slight discrepancies where that emulation wasn't perfect. This, however, no longer applies because the latest versions of Qt use the native styles API of the different platforms to draw the Qt controls.
Qt Script for Applications is a cross-platform toolkit that allows developers to make their Qt/C++ applications scriptable using an interpreted scripting language: Qt Script (based on ECMAScript/JavaScript).
Known as the ''moc'', this is a tool that is run on the sources of a Qt program prior to compiling it. The tool will generate "Meta Information" about the classes used in the program. This meta information is used by Qt to provide programming features not available in C++: The
Signal/slot System ,
Introspection and asynchrone function calls.
The use of an additional tool has been criticized for making Qt programming different from pure C++ programming. In particular, the choice of an implementation based on macros has been criticized for its absence of type safety and pollution of the namespace. This is viewed by Trolltech as a necessary trade-off to provide introspection and the dynamically generated slot and signal mechanism.
There are many programs built using the Qt toolkit, here are a few popular examples:
- Adobe Photoshop Elements , an image editing software
- Doxygen , API document generator
- Google Earth , a 3D map program
- KDE , a popular desktop environment for Linux
- --- KDELibs , a Library base for thousands of KDE applications including Amarok , K3b , KDevelop
- Motorola A760, uses Qt/Embedded in its UI
- Opera , a web browser
- Scribus , a Desktop Publishing application
- Skype , a P2P VOIP application
- TOra , a database administration tool TOra TOra uses the Qt library
- VirtualBox , a PC virtualization application
- Xconfig , Linux Kernel configuration tool
