Canvas (GUI)

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In computer science and visualization, a canvas is a container that holds various drawing elements (lines, shapes, text, frames containing other elements, etc.). It takes its name from the canvas used in visual arts. It is sometimes called a scene graph because it arranges the logical representation of a user interface or graphical scene. Some implementations also define the spatial representation and allow the user to interact with the elements via a graphical user interface.

See this article for an overview (2010-08-15) of a small handful of canvas implementations.

Library support

Various free and open-source canvas or scene graph libraries are available for developers to use to create a user interface and/ or user interface elements for their computer programs.

Example libre scene-graph canvas options include:

In C, Evas from the Enlightenment project.
In C, Clutter associated with the GNOME project.
In C++ or optionally their own markup QML, Qt Quick, provides a scenegraph associated with the Qt project.
In C++, OpenSceneGraph, a 3D graphics API using OpenGL.
In C++, the OGRE scene graph based engine supports multiple scene managers.
In C++, OpenSG, a scene graph system for real-time graphics, with clustering support and multi-thread safety.

There are canvas modules within various libraries which do not provide the power of a full scene-graph. That is, they operate at a lower level which requires the programmer to provide code such as mapping mouse-clicks to objects in the canvas. Examples libraries which include such a canvas module include:

In C++, KDE Plasma Workspaces Corona canvas
The Canvas element in HTML5
For Java, the AWT library Canvas
For Java, the Swing library Canvas
For Java, the SWT library Canvas, associated with Eclipse
For Java-like JavaScript, the GWT library Canvas
For TCL/TK, the canvas widget
For Python, the Tkinter library canvas
In C++, the FlightGear Flight Simulator canvas system
In C++, the papyrus Canvas library which renders using the cairo graphics library
In C, crcanvas, a GTK+ canvas widget which renders using the cairo graphics library
In C, GooCanvas, a GTK+ canvas widget which renders using the cairo graphics library

There are proprietary canvas libraries as well, for example:

The Microsoft Windows Win32 Canvas

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