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Qt (software)

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For the company formerly known as Qt Software, see The Qt Company.

Qt
Original author(s)Haavard Nord and Eirik Chambe-Eng[1]
Developer(s)
Initial release20 May 1995; 29 years ago (1995-05-20)[1]
Stable release6.5 LTS[2] (3 April 2023; 21 months ago (2023-04-03)) [±]
Repository
Written inC++
Operating systemAndroid, iOS, Linux (Embedded, Wayland, X11), macOS, Windows, Windows Phone, …[3]
PlatformCross-platform
TypeApplication framework
LicenseQt Commercial License[4]
GPL 2.0, 3.0[5]
LGPL 3.0[6]
Websitewww.qt.io

Qt (/kjuːt/ "cute"[7][8][9]) is a cross-platform application framework that is used for developing application software that can be run on various software and hardware platforms with little or no change in the underlying codebase, while still being a native application with native capabilities and speed. Qt is currently being developed both by The Qt Company, a company listed on the Nasdaq Helsinki Stock Exchange, and the Qt Project under open-source governance, involving individual developers and firms working to advance Qt.[10][11][12] Qt is available with both commercial[4] and open source[13] GPL 2.0, GPL 3.0, and LGPL 3.0 licenses.[5][6]

Purposes and abilities

Qt is used for developing multi-platform applications and graphical user interfaces (GUIs); however, programs without a GUI can be developed, such as command-line tools and consoles for servers. An example of a non-GUI program using Qt is the Cutelyst web framework.[14] GUI programs created with Qt can have a native-looking interface, in which case Qt is classified as a widget toolkit.

Qt uses standard C++ with extensions including signals and slots that simplify handling of events, and this helps in development of both GUI and server applications which receive their own set of event information and should process them accordingly. Qt supports many compilers, including the GCC C++ compiler and the Visual Studio suite. Qt also provides Qt Quick, that includes a declarative scripting language called QML that allows using JavaScript to provide the logic. With Qt Quick, rapid application development for mobile devices became possible, although logic can be written with native code as well to achieve the best possible performance. Qt can 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, JSON parsing, thread management and network support.

Qt market

Organizations using Qt

See also: Category:Proprietary software that uses Qt

As a commercial open source product, there are several benefits for using Qt. Among them, performance due to being native, simplicity of API, and being cross platform has lead to a wide adoption of Qt by many well-known organization like European Space Agency,[15] DreamWorks,[16][17] Lucasfilm,[18][19] Panasonic,[20] Philips,[21] Samsung,[22] Siemens,[23] Volvo,[24] Walt Disney Animation Studios,[25] Blizzard Entertainment,[26] Electronic Arts,[27] AMD, Valve Corporation.[28] In 2012, it was estimated that "over 350,000 developers are using Qt globally for numerous applications used in some 70 industries".[29] In 2017, the Qt Company estimates community of approximately 1 million developers worldwide.[30]

Qt company and its products are certified with many standards including ISO 9001:2008 certificate.[31] Qt is provided with different levels of support, for various purposes including application development and device creation. The baseline is the community support for open source users, standard and premium support from the Qt company.[32]

GUI and desktop environments

Several GUIs and desktop environments utilize Qt as widget toolkit, and it is also widely used for device creation. There are cases which famous applications have ported their entire code from other GUI toolkits to Qt, to enjoy the benefits of cross-platform native GUI with Qt. Among them, Wireshark, LXQt, VLC and Rosegarden have switched successfully from Gtk+ to Qt.

These are some of the well-known applications that use Qt:

  • AsteroidOS, an open source operating system designed for smartwatches
  • Avionics, Panasonic's Inflight Entertainment System[33][34]
  • DDE (Deepin Desktop Environment) for Linux Deepin[35][36]
  • Hawaii, a Wayland and Qt Quick-based desktop environment
  • KDE Plasma, a desktop environment for various form factors like computers, tablets and smartphones[37]
  • LiriOS, a workspace built on Qt/QML[38]
  • Lumina, a desktop environment designed for PC-BSD[39]
  • LXQt (Lightweight X11 Desktop Environment), the successor to the GTK+-based LXDE, based on Qt
  • OPIE, a GUI for the Sharp Zaurus
  • Sailfish OS, a mobile operating system developed by Jolla
  • Sky Q, the home entertainment system of Sky plc[40]
  • Tesla Model S in-car UI[41]
  • Ubuntu Touch, a phone UI developed by Canonical
  • Ultrahaptics, Haptic Interface developer for a wide range of applications.
  • webOS, a multitask operating system for smart devices like TVs and smartwatches
  • Yunit, a community-based fork of the Unity8-Shell[42]

Applications using Qt

See also: Category:Software that uses Qt and Category:Software that uses QML

Notable applications using Qt or QML are:

Editions

There are four editions of Qt available, Community, Indie Mobile, Professional and Enterprise.[62] The Community version is under the open source licenses, while the Indie Mobile, Professional and Enterprise versions, which contain additional functionality and libraries, e.g. Charts and Data Visualization, Enterprise Controls, Virtual Keyboard etc.[62] are commercially sold by The Qt Company.

Licensing

Qt is available under the following free software licenses:[13] GPL 3.0, LGPL 3.0 and LGPL 2.1 (with Qt special exception).[5][63] Note that some modules are only available under a GPL license, which means that applications which statically link to these modules need to comply with that license.[64][65]

In addition, Qt has always been available under a commercial license, like the Qt Commercial License,[4] that allows developing proprietary applications with no restrictions on licensing.


Software architecture

Example of Qt usage in Linux-based systems

Qt, when it was first released, relied on a few key concepts:

Complete abstraction of the GUI
When first released, Qt used its own paint engine and controls, emulating the look of the different platforms it runs on when it drew its widgets. This made the porting work easier because very few classes in Qt depended really on the target platform; however, this occasionally led to slight discrepancies where that emulation was imperfect. Recent versions of Qt use the native style APIs of the different platforms, on platforms that have a native widget set, to query metrics and draw most controls, and do not suffer from such issues as much.[66] On some platforms (such as MeeGo and KDE) Qt is the native API. Some other portable graphical toolkits have made different design decisions; for example, wxWidgets uses the toolkits of the target platform for its implementations.
Signals and slots
A language construct introduced in Qt for communication between objects[67] which makes it easy to implement the observer pattern while avoiding boilerplate code. The concept is that GUI widgets can send signals containing event information which can be received by other controls using special functions known as slots.
Metaobject compiler
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++: signals and slots, introspection and asynchronous function calls.

Supported platforms

Main article: List of platforms supported by Qt

Qt works on many different platforms; the following are officially supported:

Platform Description
Linux/Unix
X11 Qt for X Window System (Linux, *BSD, HP-UX, Solaris, AIX, etc.)[68]
Wayland Qt for Wayland.[69] Qt applications can switch between graphical backends like X and Wayland at load time with the -platform command line option.[70][71] This allows a seamless transition of Qt applications from X11 to Wayland.
Embedded Linux Qt for embedded platforms: personal digital assistant, smartphone, etc.[72] Exists as multiple platforms depending on display technology. DirectFB, LinuxFB and EGLFS (EGL Full Screen).
Android Qt for Android,[73] formerly known as Necessitas.[74]
Apple Platforms
macOS Qt for Apple macOS; supports applications on Cocoa[75]
iOS Qt for iOS platforms (iPhone, iPad)[76]
Microsoft Platforms
Windows Qt for Microsoft Windows XP, Vista, 7,[77] 8 and 10[78]
Windows CE Qt for Windows CE 6 and Windows Embedded Compact 7.[79]
Windows RT Support for WinRT-based Windows 8 apps and Windows Phone 8[80] With 5.4 minimum supported version: Windows Phone 8.1[81]
Other Embedded Platforms
Integrity Qt for Integrity[82]
QNX Qt for QNX[83]
VxWorks Qt for VxWorks.[84]

After Nokia opened the Qt source code to the community on Gitorious various ports appeared. There are also some ports of Qt that may be available, but are not supported anymore. These platforms are listed in List of platforms supported by Qt.

Software modules

Starting with Qt 4.0 the framework was split into individual modules.[85][86] With Qt 5.0 the architecture was modularized even further.[87][88] Qt is now split into essential and add-on modules.[89]

Qt essentials

Module Description
Qt Core The only required Qt module, containing classes used by other modules, including the meta-object system, concurrency and threading, containers, event system, plugins and I/O facilities.
Qt GUI The central GUI module. In Qt 5 this module now depends on OpenGL, but no longer contains any widget classes.
Qt Widgets Contains classes for classic widget based GUI applications and the QSceneGraph classes. Was split off from QtGui in Qt 5.
Qt QML Module for QML and JavaScript languages.
Qt Quick The module for GUI application written using QML2.
Qt Quick Controls Widget like controls for Qt Quick intended mainly for desktop applications.
Qt Quick Layouts Layouts for arranging items in Qt Quick.
Qt Network Network abstraction layer. Complete with TCP, UDP, HTTP, SSL and since Qt 5.3 SPDY support.
Qt Multimedia Classes for audio, video, radio and camera functionality.
Qt Multimedia Widgets The widgets from Qt Multimedia.
Qt SQL Contains classes for database integration using SQL.
Qt WebEngine A new set of Qt Widget and QML webview APIs based on Chromium.
Qt Test Classes for unit testing Qt applications and libraries.

Qt add-ons

Module Description
Active Qt Classes for applications which use ActiveX.
Qt Bluetooth Classes accessing Bluetooth hardware.
Qt D-Bus Classes for IPC using the D-Bus protocol.
Qt NFC Classes accessing NFC hardware. Only officially supported on BlackBerry hardware so far (or N9 in the MeeGo port).
Qt OpenGL Legacy module containing the OpenGL classes from Qt 4. In Qt 5 the similar functionality in Qt GUI is recommended.
Qt Location Classes for accessing GPS and other location services and for mapping and navigation. Split off from the Qt 4 Mobility module of Qt Location. Supported on Android, BlackBerry, iOS, Linux (using GeoClue), Windows and Sailfish OS.
Qt Script Legacy module for scripting Qt application using ECMAScript/JavaScript. In Qt 5, using similar classes in Qt QML is recommended.
Qt Sensors Classes for accessing various mobile hardware sensors. Used to be part of Qt Mobile in Qt 4. Supported on Android, BlackBerry, iOS, WinRT, Mer and Linux.
Qt Serial Port Classes for access to hardware and virtual serial ports. Supported on Windows, Linux and macOS.
Qt WebChannel Provides access to Qt objects to HTML/Js over WebSockets.
Qt WebKit Qt's WebKit implementation and API.
Qt WebKit Widgets The widget API for Qt WebKit
Qt WebSockets Provides a WebSocket implementation.
Qt XML Legacy module containing classes for SAX and DOM style XML APIs. Replaced with QXmlStreamReader and QXmlStreamWriter classes in Qt Core.
Qt XML Patterns Support for XPath, XQuery, XSLT and XML Schema validation.

Qt tools

Qt comes with its own set of tools to ease cross-platform development, which can otherwise be cumbersome due to different set of development tools. Qt Creator is a cross-platform IDE for C++ and QML. Qt Designer's GUI layout/design functionality is integrated into the IDE, although Qt Designer can still be started as a standalone tool.

In addition to Qt Creator, Qt provides qmake, a cross-platform build script generation tool that automates the generation of Makefiles for development projects across different platforms. Without such a tool, one would have to write different Makefiles for each platform, so it is useful for abstracting away the differences of various platforms.

There are other tools available in Qt, including the Qt Designer interface builder and the Qt Assistant help browser (which are both embedded in Qt Creator), the Qt Linguist translation tool, uic (user interface compiler), and moc (Meta-Object Compiler).

Programming language bindings

Main articles: List of language bindings for Qt 4 and List of language bindings for Qt 5

Qt has a range of bindings for various languages,[90] which implement some or all of its feature set.

History of Qt

The latest version of Qt is 5.9 LTS which is released on 31 May 2017, and is supported for 3 years until 31 May 2020.[91] The next planned version of Qt will be Qt 5.10, which is planned to be released on 30 November 2017[92] with several new features including initial Vulkan support for Windows, Linux and Android.[93]

Early developments

In the summer of 1990, Haavard Nord and Eirik Chambe-Eng (the original developers of Qt and the CEO and President, respectively, of Trolltech) were working together on a database application for ultrasound images written in C++ and running on Mac OS, Unix, and Windows.[1][94] They 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.[1]

The toolkit was called Qt because the letter Q looked appealing in Haavard's Emacs typeface, and "t" was inspired by Xt, the X toolkit.[1]

The first two versions of Qt had only two flavors: Qt/X11 for Unix and Qt/Windows for Windows.

On 20 May 1995 Troll Tech publicly released Qt 0.90 for X11/Linux with the source code under the Qt Free Edition License.[95][96][97] This license 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. Trolltech used this license until version 1.45. Controversy erupted around 1998 when it became clear that the K Desktop Environment 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.

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.

Becoming Free Software-friendly

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,[98] which guarantees that Qt would fall under a BSD-style license should no free/open source version of Qt be released during 12 months.[99][100]

In 2000, Qt/X11 2.2 was released under the GPL v2,[101] ending all controversy regarding GPL compatibility.

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 2002, members of the KDE on Cygwin project began porting the GPL licensed Qt/X11 code base to Windows.[102] 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.[103][104] The project achieved reasonable success although it never reached production quality.

This was resolved when Trolltech released Qt 4.0 also for Windows under the GPL in June 2005.[105] Qt 4 supported the same set of platforms in the free software/open source editions as in the proprietary edition, so it is possible, with Qt 4.0 and later releases, to create GPL-licensed free/open source applications using Qt on all supported platforms. The GPL v3 with special exception[106] 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.

Acquisition by Nokia

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.[107] 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.

On 14 January 2009, Qt version 4.5 added another option, the LGPL,[108] which should make Qt even more attractive for non-GPL open source projects and for closed applications.[109]

In February 2011, Nokia announced its decision to drop Symbian technologies and base their future smartphones on the Windows Phone platform instead.[110] One month later, Nokia announced the sale of Qt's commercial licensing and professional services to Digia, with the immediate goal of taking 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.

Merging and demerging with Digia

In March 2011, Nokia sold the commercial licensing part of Qt to Digia creating Qt Commercial.[111] In August 2012, Digia announced that it would acquire Qt from Nokia.[112] The Qt team at Digia started their work in September 2012.[113] They released Qt 5.0 within a month and newer versions every 6 months with new features and additional supported platforms.

In September 2014, Digia transferred the Qt business and copyrights to their wholly owned subsidiary, The Qt Company, which owns 25 brands[114] related to Qt. In May 2016, Digia and Qt have demerged completely into two independent companies.[115]

The Qt Project and Open Governance

Qt 5 was officially released on 19 December 2012. This new version marked a major change in the platform, with hardware-accelerated graphics, QML and JavaScript playing a major role. The traditional C++-only QWidgets continued to be supported, but did not benefit from the performance improvements available through the new architecture.[116] Qt 5 brings significant improvements to the speed and ease of developing user interfaces.[117]

Framework development of Qt 5 moved to open governance, taking place at qt-project.org. There it is now possible for developers outside Digia to submit patches and have them reviewed.[118]

See also

References

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Bibliography

Qt Wiki provides a comprehensive list of English books about Qt. [1] This is a list of notable books:

Wikimedia Commons has media related to Qt.
Wikibooks has a book on the topic of: Qt
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