GTK

Development tools

GUI designers

There are several GUI designers for GTK. Here is a selection of GTK GUI designers:

• Cambalache – a successor to Glade, supports GTK 4.
• Glade – supports GtkBuilder, which is a GTK built-in GUI description format. (not actively maintained)
• 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
• Lazarus (on Linux defaults to interfacing with GTK 2)

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. It was introduced with GTK version 3.14.

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
• Detailed object inspection (type, state, properties, CSS, actions, etc.)
• Global application information display
• CSS rule debugging
• Rendering pipeline recording and inspection

Development

GTK is mainly developed by The GNOME Project, which also develops the GNOME Development Platform and the GNOME Desktop Environment. GTK is mainly written in C. 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. 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, 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.

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. As a result, application and theme developers often have to rewrite parts of their code to ensure compatibility with newer versions 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. Before its release, Benjamin Otte said that GTK 4 would lower the pressure to innovate and move GTK towards 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. 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.

• Aurélien Gâteau started Gwenview as an GTK application but switched to Qt early in development.
• 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, 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.
• 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.
• EasyEffects, a popular audio equalizer, is being ported to Qt.

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 for which GTK was created
• GNOME Core Applications, a collection of applications as a standard bundle of the GNOME desktop environment
• GNOME Circle, a collection of applications created to work within the GNOME ecosystem
• 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
• REAPER, a digital audio workstation (DAW)
• Remmina, a remote desktop client
• Transmission, a BitTorrent client

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. Other ports include DirectFB (for example used by the Debian installer).

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 & 4, 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

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

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.

GTK 2

The GTK 2.0.0 release (2002) 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.

GTK 3

GTK version 3.0.0 (2011) 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.

The '+' was dropped returning to simply 'GTK' in February 2019 during a Hackathon.

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.

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.

Releases