The GTK team releases new versions on a regular basis.[6] GTK 4 and GTK 3 are maintained, while GTK 2 is
end-of-life.[7] GTK1 is independently maintained by the
CinePaint project.[8]
Software architecture
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 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.[10][11]
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.[12] Since GTK version 3.0, all rendering is done using Cairo.[13]
On January 26, 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.[14] On February 6, 2019 it was announced that GTK 4 will drop the “+” from the project's name.[3]
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.[15][16]
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[17]
Crow Designer, relies on its own GuiXml format and GuiLoader library.[18]
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.
Gtk# is a set of
.NET Framework bindings for the GTK
graphical user interface (GUI)
toolkit and assorted
GNOMElibraries. 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.[citation needed]
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.[21]
In addition to support the standard GTK/GNOME stack of development tools, the gtk-dotnet.dll 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.[citation needed]
As of September 2020[update], 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.[22]
Development
GTK is mainly developed by
The GNOME Project, which also develops the GNOME Development Platform and the GNOME Desktop Environment.[23]
GTK development is loosely managed. Discussion chiefly occurs on several public mailing lists.[24] GNOME developers and users gather at an annual GNOME Users And Developers European ConferenceGUADEC meeting to discuss GNOME's current state and future direction.[25] GNOME incorporates standards and programs from
freedesktop.org to better
interoperate with other desktops.[citation needed]
On September 1, 2016, a post on the GTK development blog denoted, among other things, the future numbering scheme of GTK.[27] 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.[28]
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.[29] 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.[30]
Since August 14, 2017, the master branch of GTK has been built with
Meson, and the Autotools build system files have been dropped.[31]
Criticism
The most common criticism of GTK is the lack of backward-compatibility in major updates, most notably in the
application programming interface (API)[32] and theming.[33]
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.[34] 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.[35]
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.[36]
The
Audacious music player moved to Qt in version 3.6.[37] 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."[38]
Wireshark has switched to Qt due to not having a good experience with GTK's cross-platform support.[39]
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.[40] Other ports include
DirectFB (used by the
Debian installer, for example) and
ncurses.[41]
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.[citation needed]
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.[42] Finally GTK was re-written to be
object-oriented and was renamed GTK+.[43] 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.[44]
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.[47]
GTK 2.24.10 and 3.6.4 is available in Internet, but very buggy and limited against actual versions.[48][49]
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.[50]
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.[51] The latest version of GTK for OpenVMS is version 1.2.10.[52]
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 January 2018 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.[53]
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.[108]
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).[111] 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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