GTK

GTK (formerly GIMP ToolKit and GTK+) is a free and open-source cross-platform widget toolkit for creating graphical user interfaces (GUIs). It is licensed under the terms of the GNU Lesser General Public License, allowing both free and proprietary software to use it. It is one of the most popular toolkits for the Wayland and X11 windowing systems.
The GTK team releases new versions on a regular basis. GTK 4 and GTK 3 are maintained, while GTK 2 is end-of-life. GTK1 is independently maintained by the CinePaint project.
Software architecture
The GTK library contains a set of graphical control elements (widgets); version 3.22.16 contains 186 active and 36 deprecated widgets. GTK is an object-oriented widget toolkit written in the programming language C; it uses GObject, that is the GLib object system, for the object orientation. While GTK is mainly for windowing systems based on X11 and Wayland, 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.
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.
Starting with version 2.8, released in 2005, GTK began the transition to using Cairo to render most of its graphical control elements widgets. Since GTK version 3.0, all rendering is done using Cairo.
On 26 January 2018 at DevConf.cz, Matthias Clasen gave an overview of the current state of GTK 4 development, including a high-level explanation of how rendering and input worked in GTK 3, what changes are being made in GTK 4 (>3.90), and why. On 6 February 2019 it was announced that GTK 4 will drop the “+” from the project's name.
GTK Drawing Kit (GDK)
GDK acts as a wrapper around the low-level functions provided by the underlying windowing and graphics systems.
GTK Scene Graph Kit (GSK)
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.
GtkInspector
GtkInspector was introduced with version 3.14.
GtkInspector can only be invoked after installing the development package libgtk-3-dev/gtk+-devel.
GUI designers
There are several GUI designers for GTK. The following projects were active as of July 2011:
Glade, supports GtkBuilder, which is a GTK built-in GUI description format.
Gazpacho, GUI builder for the GTK toolkit written in Python
Crow Designer, relies on its own GuiXml format and GuiLoader library.
Stetic, part of MonoDevelop, oriented toward Gtk#.
Gambas since version 2.0 atop BASIC
Xojo on Linux
Lazarus on Linux defaults to interfacing with GTK 2
GtkBuilder
GtkBuilder allows user interfaces to be designed without writing code. The interface is described in an Extensible Markup Language (XML) file, which is then loaded at runtime and the objects created automatically. The Glade Interface Designer allows creation of the user interface in a what you see is what you get (WYSIWYG) manner. 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.
GtkSharp, not to be confused with Gtk#, supports GTK 3.
Gtk#
Gtk# is a set of .NET Framework bindings for the GTK graphical user interface (GUI) toolkit and assorted GNOME libraries. The library facilitates building graphical GNOME applications using Mono or any other compliant Common Language Runtime (CLR). Gtk# is an event-driven system like any other modern windowing library where every widget allows associating handler methods, which get called when certain events occur.
Applications built using Gtk# will run on many platforms including Linux, Windows and macOS. The Mono packages for Windows include GTK, Gtk# and a native theme to make applications look like native Windows applications. Starting with Mono 1.9, running Gtk# applications on macOS no longer requires running an X11 server.
Glade Interface Designer can be used with the Glade# bindings to easily design GUI applications. A GUI designer named Stetic is integrated with the MonoDevelop integrated development environment (IDE).
In addition to support the standard GTK/GNOME stack of development tools, the assembly provides a bridge to consume functionality available on the .NET stack. At this point this includes the functionality to use System.Drawing to draw on a widget.
, Gtk# support for Gtk3 remains in the preview phase and forked projects, such as GtkSharp, have been founded to provide full Gtk3 support for C# and other CLI languages. The lack of a released version of Gtk# with support for Gtk3 was cited as a reason to remove the Banshee media player in Ubuntu 12.04.
Development
GTK is mainly developed by The GNOME Project, which also develops the GNOME Development Platform and the GNOME Desktop Environment.
GTK development is loosely managed. Discussion chiefly occurs on several public mailing lists. 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. GNOME incorporates standards and programs from freedesktop.org to better interoperate with other desktops.
GTK is mainly written in C. Many language bindings are available.
On 1 September 2016 a post on the GTK development blog denoted, among other things, the future numbering scheme of GTK. GTK version 3.22, released in Autumn 2016, was planned to be the last 3.x release, although version 3.24 followed in Fall 2018 with the delay of GTK 4.
The development of GTK 4 used version names 3.90, 3.92, etc. until the first GTK 4.0 stable release was launched in December 2020. Despite the first stable GTK 4 release, some applications using GTK still rely on GTK 2. For example, as of January 2022, GIMP is still being ported to GTK 3.
Build automation
GTK (and GNOME, GLib, etc.) formerly utilized the GNU Build System (named Autotools) as the build automation system of choice.
Since 14 August 2017, the master branch of GTK has been built with Meson, and the Autotools build system files have been dropped.
Criticism
The most common criticism of GTK is the lack of backward-compatibility in major updates, most notably in the application programming interface (API) and theming.
The compatibility breaks between minor releases during the GTK 3.x development cycle was explained 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. 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.
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.
Hong Jen Yee, developer of LXDE (the GTK version of which was dropped and all efforts focused on the Qt port), expressed disdain for version 3 of the GTK toolkit's radical API changes and increased memory usage, and ported PCMan File Manager (PCManFM) to Qt. PCManFM is being developed with a GTK and with a Qt backend at the same time.
The Audacious music player moved to Qt in version 3.6. 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."
Wireshark has switched to Qt due to not having a good experience with GTK's cross-platform support.
Use
Applications
Some notable applications that use GTK as a widget toolkit include:
Ardour, a digital audio workstation (DAW)
Deluge, a BitTorrent client
Foliate, an ebook reader
GIMP, a raster graphics editor
GNOME Builder, an integrated development environment (IDE)
GNOME Core Applications, a collection of applications as a standard bundle of the GNOME desktop environment
GNOME Evolution, a personal information manager
HandBrake, digital video transcoder
Inkscape, a vector graphics editor
LibreOffice, an office suite
Lutris, a game manager
Mozilla Firefox, a web browser
Mozilla Thunderbird, a personal information manager
Pitivi, a video editor
PCSX-Reloaded, a video game console emulator
Remmina, a remote desktop client
Transmission, a Bit Torrent client
Desktop environments
Several desktop environments utilize GTK as the widget toolkit.
Current
GNOME, based on GTK, meaning that programs native to GNOME use GTK
Budgie, built from scratch for the SolusOS successor, Solus Operating System
Cinnamon, a fork of GNOME 3 which uses GTK version 3
MATE, a fork of GNOME 2 which uses GTK 3 since version 1.18
Xfce, based on GTK 3 since version 4.14
Pantheon uses GTK 3 exclusively, being developed by elementary OS
Sugar, a desktop environment for youth primary education, which uses GTK, especially PyGTK
Phosh, a mobile UI designed for PureOS
LXDE (Lightweight X11 Desktop Environment) is based on GTK 2
Unity, the former default desktop environment of Ubuntu
Inactive
Access Linux Platform (successor of the Palm OS PDA platform)
Consort, the GNOME 3.4 Fallback Mode – fork from Solus
GPE, the GPE Palmtop Environment
ROX Desktop, a lightweight desktop, with features from the GUI of RISC OS
Miscellaneous
GTK programs can be run on desktop environments based on X11 and Wayland, or window managers even those 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, where it is used by some popular cross-platform applications like Pidgin and GIMP. wxWidgets, a cross-platform GUI tool-kit, uses GTK on Linux by default. Other ports include DirectFB (used by the Debian installer, for example) and ncurses.
Window managers
The following window managers use GTK:
Aewm
AfterStep
Amaterus
Consortium
IceWM
Marco
Metacity
Muffin
Mutter
Sawfish
Wmg
Xfwm
GtkSourceView
For syntax highlighting there is GtkSourceView, "source code editing widget". GtkSourceView is maintained by GNOME separately from GTK as a library: gtksourceview. There are plans to rename to gsv.
GtkSpell
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
Linux
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. Finally GTK was re-written to be object-oriented and was renamed GTK+. 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.
The GTK 2.0.0 release 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, GTK 2 depends on the Cairo graphics library for rendering vector graphics.
GTK version 3.0.0 included revised input device handling, support for themes written with CSS-like syntax, and the ability to receive information about other opened GTK applications.
The '+' was dropped returning to simply 'GTK' in February 2019 during a Hackathon.
macOS
With Quartz-backend GTK is available in macOS.
Windows
After GTK 2.24.10 and 3.6.4 Development of Windows with Installer was closed by Gnome. Installation of MSYS2 on Windows is a good way to use actual GTK.
GTK 2.24.10 and 3.6.4 is available in Internet, but very buggy and limited against actual versions.
A version for Windows 64-bit is prepared by Tom Schoonjans with 2.24.33 (actual like Linux) and 3.24.24 (actual like Linux) from January 2021 available.
Windows 10's Fall Creators Update includes Windows Subsystem for Linux (WSL). With Linux distributions like Ubuntu or Debian available from the Microsoft Store and an X server like Xming or VcXsvr, thousands of programs like GTK 2 or 3 can run with X or terminal support.
OpenVMS
HP stated that their goal was to merge the needed OpenVMS changes into the GTK Version 1.3 development stream, however this never materialised. The latest version of GTK for OpenVMS is version 1.2.10.
GTK 4
One of the cardinal novelties implemented during the GTK 4 development cycle (i.e. GTK 3.92, etc.) has been the removal of customization options for the user side (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.
the event handling from signal handlers described by GtkWidget is delegated to event controllers
the rendering is delegated to GtkSnapshot objects
the layout mechanism from GtkWidget is delegated to GtkLayoutManager
In 2018-Jan-26 at 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.
Releases
See also
Client-Side Decoration
List of widget toolkits
gtkmm – C++ bindings for GTK
Enlightenment Foundation Libraries (EFL) – widget toolkit written for the Enlightenment window manager
FLTK – a light, cross-platform, non-native widget toolkit
Fox toolkit – a fast, open source, cross-platform widget toolkit
IUP – a multi-platform toolkit for building native graphical user interfaces
Ultimate++
Visual Component Library (VCL)
References
Bibliography
External links
Application programming interfaces
Articles with example C code
C (programming language) libraries
Cross-platform software
Free computer libraries
Free software programmed in C
GNOME
Software that uses Cairo (graphics)
Software that uses Meson
Software using the LGPL license
Widget toolkits
X-based libraries