The GTK team releases new versions on a regular basis.[6] GTK 4 and GTK 3 are actively maintained, while GTK 2 is no longer supported.[7] GTK 1 is independently maintained by the CinePaint project.[8]
The GTK toolkitSimplified software architecture of GTK. Pango, GDK, ATK, GIO, Cairo and GLibGDK contains back-ends to X11, Wayland, Broadway (HTTP), Quartz, and GDI and relies on Cairo for the rendering. Its new SceneGraph is work-in-progress.
Parts of this software (those related to section) need to be updated. Please update this software to reflect recent events or newly available information. (May 2024)
The GTK library contains a set of graphical control elements (widgets); version 3.22.16 contains 186 active and 36 deprecated widgets.[9] GTK is an object-orientedwidget toolkit written in the programming language C; it uses GObject (that is, the GLib object system) for object orientation. While GTK is mainly used with windowing systems based on Wayland (and prior to that on Wayland's predecessor X11), it works on other platforms, including Microsoft Windows (interfaced with the Windows API), and macOS (interfaced with Quartz). There is also an HTML5 back-end named Broadway, although this was deprecated in 2025 with the X11 backend to indicate both would be removed in GTK version 5.[10][11][12] GTK uses Vulkan or GL to draw most graphical elements.[13]
GTK can be configured to change the look of the widgets drawn; this is done using different display engines. Several display engines exist which try to emulate the look of the native widgets on the platform in use.
GSK is the rendering and scene graph API for GTK. GSK lies between the graphical control elements (widgets) and the rendering. GSK was finally merged into GTK version 3.90 released March 2017.
GtkBuilder
GtkBuilder allows user interfaces to be designed without writing code. The interface is described in an Extensible Markup Language (XML) file which is written by hand or generated by a GUI designer, which is then loaded at runtime and the objects created automatically. The description of the user interface is independent from the programming language being used.
Language bindings
Language bindings are available for using GTK from languages other than C, including C++, Genie, JavaScript, Perl, Python, Vala, and others.[14]
Backends
GTK supports various backends, which provides different ways to display GTK applications depending on the system and environment. Examples of GTK backends are:
Wayland – Used with the Wayland display server on Linux systems, it is a modern replacement for X11.
X11 – The default on Linux systems using the X.Org display server.
Lazarus (on Linux defaults to interfacing with GTK 2)
GTK Inspector
A screenshot of the GTK Inspector
The GTK Inspector is a built-in interactive debugging tool in GTK, allowing developers to inspect and modify UI elements, test CSS changes, and analyze widget structure in real time. It can be enabled using the Control + Shift + I or Control + Shift + D shortcuts, or by setting the GTK_DEBUG=interactive environment variable.[19] It was introduced with GTK version 3.14.[20][21]
Features
Interactive debugging
Real-time CSS testing and modifications
Widget magnification for detailed inspection
UI structure analysis and object property examination
Customizable display settings via environment variables
GTK is mainly developed by The GNOME Project, which also develops the GNOME Development Platform and the GNOME Desktop Environment.[22] GTK is mainly written in C.[23] Many language bindings are available.
GNOME developers and users gather at an annual GNOME Users And Developers European Conference GUADEC meeting to discuss GNOME's current state and future direction.[24] GNOME incorporates standards and programs from freedesktop.org to better interoperate with other desktops.
Many GNOME applications have been ported to GTK 4, which was released in December 2020,[25] however some still use GTK+ 3 (GIMP being a major one).
Build automation
The master branch of GTK utilizes Meson for its build automation. GTK (and GNOME, GLib, etc.) formerly utilized the GNU Build System (named Autotools) as the build automation system of choice. Since August 14, 2017, the Autotools build system files have been dropped.[26]
Criticism
The most common criticism of GTK is the lack of backward-compatibility in major updates, most notably in the application programming interface (API)[27] and theming.[28] The result is that application developers or theme developers have to rewrite parts of their code to make it work with a newer version of GTK.
The compatibility breaks between minor releases during the GTK 3.x development cycle was explained in 2013 by Benjamin Otte as due to strong pressures to innovate, such as providing the features modern users expect and supporting the increasingly influential Wayland display server protocol. With the release of GTK 4, the pressure from the need to innovate will have been released and the balance between stability and innovation will tip toward stability.[29] Similarly, recent changes to theming are specifically intended to improve and stabilise that part of the API, meaning some investment now should be rewarded later. However, in 2025, GTK 5 is described in the official documentation as "a major new version of GTK that breaks both API and ABI compared to GTK 4.x.", like GTK 3 and 4.[30][31][32]
Aurélien Gâteau started Gwenview as GTK application but switched to Qt early in development.[33]
Dirk Hohndel, codeveloper of Subsurface and member of Intel's Open-Source Technology Center, criticized the GTK developers for being abrasive and ignoring most community requests.[34]
Hong Jen Yee, the creator of LXDE, expressed disdain for the GTK3 toolkit's radical breaking API changes and increased memory usage, leading him to port the project to Qt, renaming it LXQt.[35]
The Audacious music player moved to Qt in version 3.6.[36] The reasons stated by the developers for this include a transition to client-side window decorations, which they claim cause the application to look "GNOME-y and out of place."[37]
Wireshark has switched to Qt due to not having a good experience with GTK's cross-platform support.[38]
EasyEffects, a popular audio equalizer, is being ported to Qt.[39]
Use
GTK's support for Wayland requires applications to be adapted to Wayland as well.Screenshot of GIMP 2.8 - GTK is responsible for managing the interface components of the program, including the menus, buttons, and input fields.
Applications
Some notable applications that use GTK as a widget toolkit include:
GTK programs can be run on desktop environments based on X11 and Wayland, or others including ones not made with GTK, provided the needed libraries are installed; this includes macOS if X11.app is installed. GTK can be also run on Microsoft Windows. It is used by some popular cross-platform applications like Pidgin and GIMP. wxWidgets, a cross-platform GUI toolkit, uses GTK on Linux by default.[40] Other ports include DirectFB (for example used by the Debian installer).
GtkSpell is a library separate from GTK. GtkSpell depends on GTK and Enchant. Enchant is a wrapper for ispell, hunspell, etc., the actual spell checker engine/software. GtkSpell uses GTK's GtkTextView widget, to highlight misspelled words and offer replacement.
History
GTK was originally designed and used in the GNU Image Manipulation Program (GIMP) as a replacement of the Motif toolkit; at some point Peter Mattis became disenchanted with Motif and began to write his own GUI toolkit named the GIMP toolkit and had successfully replaced Motif by the 0.60 release of GIMP.[41] Finally GTK was re-written to be object-oriented and was renamed GTK+.[42] This was first used in the 0.99 release of GIMP. GTK was subsequently adopted for maintenance by the GNOME Foundation, which uses it in the GNOME desktop environment.
GTK 2
The GTK 2.0.0 release (2002[43]) series introduced new features which include improved text rendering using Pango, a new theme engine, improved accessibility using the Accessibility Toolkit, transition to Unicode using UTF-8 strings, and a more flexible API. Starting with version 2.8, released in 2005, GTK 2 depends on the Cairo graphics library for rendering vector graphics.[44]
GTK 3
GTK version 3.0.0 (2011[45]) included revised input device handling, support for themes written with CSS-like syntax, and the ability to receive information about other opened GTK applications. All rendering was done using Cairo.[46]
The '+' was dropped returning to simply 'GTK' in February 2019 during a Hackathon.[47]
GTK 4
Release of the first GTK 4 version was in December 2020. At the 2018 edition of DevConf.cz, Matthias Clasen gave an overview of the then-current state of GTK 4 development, including a high-level explanation of how rendering and input worked in GTK 3, what changes were being made to GTK 4, and the reasons for those changes. Examples of things that have become possible with GTK 4 were given as well.[48]
One of the main changes made during the GTK 4 development cycle (i.e. GTK 3.92, etc.) was the removal of user customization options (like individual keyboard shortcuts that could be set in GTK+ 2), and the delegation of functionality to ancillary objects instead of encoding it into the base classes provided by GTK. Other changes include:
Event handling from signal handlers described by GtkWidget is delegated to event controllers.
Rendering is delegated to GtkSnapshot objects.
The layout mechanism is delegated from GtkWidget to GtkLayoutManager.
Cairo was de-emphasized and Vulkan or GL were used instead to draw most graphical elements.[13]
To remove much of the necessary IPC between the X11 application and the X11 server, GDK is rewritten (mainly by Alexander Larsson) to use "client-side windows", i.e., the GdkWindow, which every widget must have, belongs now to the client
The gtk4-builder-toolsimplify command has gained a --3to4 option to convert GTK3 ui files to GTK4; though with AMTK menus, toolbars or other objects like GtkShortcutsWindow are created programmatically (not with a *.ui file), but with convenient APIs.[104]
GtkWidget can now use a GtkLayoutManager for size allocation
layout managers can optionally use layout children holding layout properties
GtkBinLayout, GtkBoxLayout, GtkGridLayout, GtkFixedLayout and GtkCustomLayout are currently available
more layout manager implementations will appear in the future
Focus handling has been rewritten, and focus-change event generation has been unified with crossing events
Events have been simplified and are just used for input:
expose events have been replaced by a GdkSurface::render signal
configure events have been replaced by a GdkSurface::size-changed signal
map events have been replaced by a GdkSurface::mapped property
gdk_event_handler_set has been replaced by a GdkSurface::event signal
Introduced successor to Accessibility Toolkit (ATK).[107] The new approach will implement WAI-ARIA (World Wide Web Consortium (W3C) Accessibility Initiative – Accessible Rich Internet Applications).
Updated headers to use standard C types instead of GLib types
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↑Taylor, Owen (December 22, 2002). "GTK+-2.2.0 released". GNOME Mail Services (Mailing list). Archived from the original on August 10, 2020. Retrieved May 20, 2019.
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