A widget toolkit, widget library, GUI toolkit, or UX library is a

library A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...

or a collection of libraries containing a set of

graphical control element A graphical widget (also graphical control element or control) in a graphical user interface is an element of interaction, such as a button or a scroll bar. Controls are software components that a computer user interacts with through direct ...

s (called ''widgets'') used to construct the

graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...

(GUI) of programs. Most widget toolkits additionally include their own

rendering engine Rendering or image synthesis is the process of generating a physically-based rendering, photorealistic or Non-photorealistic rendering, non-photorealistic image from a 2D model, 2D or 3D model by means of a computer program. The resulting im ...

. This engine can be specific to a certain

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

windowing system In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP (windows, icons, menus, pointer) paradigm for ...

or contain back-ends to interface with more multiple ones and also with rendering APIs such as

OpenGL OpenGL (Open Graphics Library) is a cross-language, cross-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API is typically used to interact with a graphics processing unit (GPU), to achieve hardwa ...

OpenVG OpenVG is an API designed for hardware-accelerated 2D vector graphics. Its primary platforms are mobile phones, gaming & media consoles and consumer electronic devices. It was designed to help manufacturers create more attractive user interfaces ...

, or EGL. The

look and feel In software design, the look and feel of a graphical user interface comprises aspects of its design, including elements such as colors, shapes, layout, and typefaces (the "look"), as well as the behavior of dynamic elements such as buttons, boxes ...

of the graphical control elements can be hard-coded or decoupled, allowing the graphical control elements to be themed/ skinned.

Overview

Some toolkits may be used from other languages by employing

language binding In programming and software design, binding is an application programming interface (API) that provides glue code specifically made to allow a programming language to use a foreign library or operating system service (one that is not native to th ...

Graphical user interface builder A graphical user interface builder (or GUI builder), also known as GUI designer or sometimes RAD IDE, is a software development tool that simplifies the creation of GUIs by allowing the designer to arrange graphical control elements (often calle ...

s such as e.g.

Glade Interface Designer Glade Interface Designer is a graphical user interface builder for GTK, with additional components for GNOME. In its third version, Glade is programming language–independent, and does not produce code for events, but rather an XML fil ...

facilitate the authoring of GUIs in a

WYSIWYG In computing, WYSIWYG ( ), an acronym for What You See Is What You Get, is a system in which editing software allows content to be edited in a form that resembles its appearance when printed or displayed as a finished product, such as a printed d ...

manner employing a

user interface markup language A user interface markup language is a markup language that renders and describes graphical user interfaces and controls. Many of these markup languages are dialects of XML and are dependent upon a pre-existing scripting language engine, usually ...

such as in this case

GtkBuilder 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 propriet ...

. The GUI of a program is commonly constructed in a cascading manner, with graphical control elements being added directly to on top of one another. Most widget toolkits use

event-driven programming In computer programming, event-driven programming is a programming paradigm in which the flow of the program is determined by events such as user actions ( mouse clicks, key presses), sensor outputs, or message passing from other programs or t ...

as a model for interaction.Past, Present and Future of User Interface Software Tools
Brad Myers, Scott E. Hudson, Randy Pausch, Y Pausch. ACM Transactions on Computer-Human Interaction, 2000

/ref> The toolkit handles Event handler, user events, for example when the user clicks on a

button A button is a fastener that joins two pieces of fabric together by slipping through a loop or by sliding through a buttonhole. In modern clothing and fashion design, buttons are commonly made of plastic but also may be made of metal, wood, ...

. When an event is detected, it is passed on to the application where it is dealt with. The design of those toolkits has been criticized for promoting an oversimplified model of event-action, leading programmers to create error-prone, difficult to extend and excessively complex

application code This glossary of computer software terms lists the general terms related to computer software, and related fields, as commonly used in Wikipedia articles. Glossary See also * Outline of computer programming * Outline of soft ...

Finite state machine A finite-state machine (FSM) or finite-state automaton (FSA, plural: ''automata''), finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number o ...

s and hierarchical state machines have been proposed as high-level models to represent the interactive state changes for reactive programs.

Windowing systems

window A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent materia ...

is considered to be a graphical control element. In some windowing systems, windows are added directly to the scene graph (canvas) by the

window manager A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment. They work in conjunction ...

, and can be stacked and layered on top of each other through various means. Each window is associated with a particular application which controls the widgets added to its canvas, which can be watched and modified by their associated applications.

References

{{X desktop environments and window managers Graphical user interfaces