The Qt designer used for GUI designing
|Original author(s)||Haavard Nord and Eirik Chambe-Eng|
|Developer(s)||Qt Project, Digia|
|Initial release||May 1995|
|Stable release||5.0.2 / 10 April 2013|
|Preview release||5.1 Beta / 14 May 2013|
|Operating system||Linux (Embedded, Wayland, X11), OS X, Windows, …|
|License||GNU Lesser General Public License v2.1 (Qt open-source version)
Qt Commercial License (Qt Commercial version)
Qt (// "cute", or unofficially as Q-T cue-tee) is a cross-platform application framework that is widely used for developing application software with a graphical user interface (GUI) (in which cases Qt is classified as a widget toolkit), and also used for developing non-GUI programs such as command-line tools and consoles for servers.
Qt uses standard C++ but makes extensive use of a special code generator (called the Meta Object Compiler, or moc) together with several macros to enrich the language. Qt can also be used in several other programming languages via language bindings. It runs on the major desktop platforms and some of the mobile platforms. It has extensive internationalization support. Non-GUI features include SQL database access, XML parsing, thread management, network support, and a unified cross-platform application programming interface (API) for file handling.
Qt is developed by Digia, who owns the Qt technology and trademark, and the Qt Project under open governance, involving individual developers and firms working to advance Qt. Before the launch of the Qt Project, it was produced by Nokia's Qt Development Frameworks division, which came into existence after Nokia's acquisition of the Norwegian company Trolltech, the original producer of Qt. In February 2011 Nokia announced its decision to drop Symbian technologies and base their future smartphones on Microsoft platform instead. One month later Nokia announced the sale of Qt's commercial licensing and professional services to Digia, with the immediate goal of bringing Qt support to Android, iOS and Windows 8 platforms, and to continue focusing on desktop and embedded development, although Nokia was to remain the main development force behind the framework at that time. On 9 May, it was announced on the Qt Labs website that the groundwork was being laid for the next major version of Qt, with the expectation that Qt 5 would be released in August 2012.
Qt works on the following platforms:
Since Nokia opened the Qt source code to the community on Gitorious various ports have been appearing. Here are some of them:
There are three editions of Qt available on each of these platforms, namely:
Qt is available under the following copyright licenses:
Trolltech released Qt 4.0 on 28 June 2005 and introduced five new technologies in the framework:
|Version||Release date||New features|
|4.1||20 December 2005||Introduced integrated SVG Tiny support, a PDF backend to Qt's printing system, and a few other features.|
|4.2||4 October 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.|
|4.3||30 May 2007||Improved Windows Vista support, improved OpenGL engine, SVG file generation, added QtScript (ECMAScript scripting engine based on QSA).|
|4.4||6 May 2008||Features included are improved multimedia support using Phonon, enhanced XML support, a concurrency framework to ease developing multi-threaded applications, an IPC framework with a focus on shared memory, and WebKit integration.|
|4.5||3 March 2009||Major included features are QtCreator, improved graphical engine, improved integration with WebKit, OpenDocument Format write support and new licensing options, as well as OS X Cocoa framework support.|
|4.6||1 December 2009||New APIs are Framework Animation, Gestures, Multi-touch. Now supports (as Tier 1) Symbian and (as Tier 2) Windows 7 and Mac OS X 10.6, support extended for some Unix systems. Improvements have also been made to overall performance.|
|4.7||21 September 2010||QML and Qt Quick.|
|4.8||15 December 2011||Qt Platform Abstraction, Threaded OpenGL support, Multithreaded HTTP, and optimized file system access.|
Framework development of Qt 5 moved to open governance, taking place at qt-project.org. It is now possible for developers outside Nokia/Digia to submit patches and have them reviewed.
|Version||Release date||New features|
|5.0||19 December 2012||Major overhaul of the Qt 4.x series.
Complete Wayland support, including the client-side decorations.
|5.1||June 2013 (ETA)||New modules and experimental Android and iOS support.|
The innovation of Qt when it was first released relied on a few key concepts.
Qt used to emulate the native look of its intended platforms, which occasionally led to slight discrepancies where that emulation was imperfect. Recent versions of Qt use the native style APIs of the different platforms to query metrics and draw most controls, and so do not suffer from such issues as much.
On some platforms (such as MeeGo and KDE) Qt is the native API.
The metaobject compiler, termed moc, is a tool that is run on the sources of a Qt program. It interprets certain macros from the C++ code as annotations, and uses them to generate added C++ code with Meta Information about the classes used in the program. This meta information is used by Qt to provide programming features not available natively in C++: the signal/slot system, introspection and asynchronous function calls.
Haavard Nord and Eirik Chambe-Eng (the original developers of Qt and the CEO and President, respectively, of Trolltech) 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 first two versions of Qt had only two flavors: Qt/X11 for Unix and Qt/Windows for Windows. The Windows platform was only available under a proprietary license, which meant free/open source applications written in Qt for X11 could not be ported to Windows without purchasing the proprietary edition.
At the end of 2001, Trolltech released Qt 3.0, which added support for Mac OS X. The Mac OS X support was available only in the proprietary license until June 2003, when Trolltech released Qt 3.2 with Mac OS X support available under the GPL.
In June 2005, Trolltech released Qt 4.0.
Nokia acquired Trolltech ASA on 17 June 2008 and changed the name first to Qt Software, then to Qt Development Frameworks. Since then it focused on Qt development to turn it into the main development platform for its devices, including a port to the Symbian S60 platform. Version 1.0 of the Nokia Qt SDK was released on 23 June 2010. The source code was made available over Gitorious, a community oriented git source code repository, to gather an even broader community that is not only using Qt but also helping to improve it.
At all times, Qt was available under a commercial license that allows developing proprietary applications with no restrictions on licensing. In addition, Qt has been gradually made available under several increasingly free licenses.
Until version 1.45, source code for Qt was released under the FreeQt license. This was viewed as not compliant with the open source principle by the Open Source Initiative and the free software definition by Free Software Foundation because, while the source was available, it did not allow the redistribution of modified versions.
Controversy erupted around 1998 when it became clear that KDE's KDE Software Compilation was going to become one of the leading desktop environments for Linux. As it 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.
With the release of version 2.0 of the toolkit, the license was changed to the Q Public License (QPL), a free software license but one regarded by the Free Software Foundation as incompatible with the GPL. Compromises were sought between KDE and Trolltech whereby Qt would not be able to fall under a more restrictive license than the QPL, even if Trolltech was bought out or went bankrupt. This led to the creation of the KDE Free Qt foundation, which guarantees that Qt would fall under a BSD-style license should no free/open source version of Qt be released during 12 months.
In 2000, Qt 2.2 was released under the GPL v2, ending all controversy regarding GPL compatibility.
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/open source software platform. 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 GPL v3 with special exception was later added as an added licensing option. The GPL exception allows the final application to be licensed under various GPL-incompatible free software/open source licenses such as the Mozilla Public License 1.1.
In March 2011, Nokia sold the commercial licensing part of Qt to Digia creating Qt Commercial.
Qt is most notably used in Autodesk Maya, BlackBerry, Dassault DraftSight, Mathematica, European Space Agency, DreamWorks, Google, HP, KDE, Lucasfilm, The Foundry's Nuke,  Panasonic, Philips, Samsung, Siemens, Skype, Ubuntu, VirtualBox, VLC media player, Volvo, and Walt Disney Animation Studios.
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