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.
Various free and open-source canvas or scene-graph libraries allow developers to construct a user interface and/or user-interface elements for their computer programs.
Examples of free and open-source scene-graph canvas options include:
in C, Evas from the Enlightenment project
in C, Clutter, associated with the GNOME project
in C, GTK+ Scene Graph Kit (GSK)
in C, Pigment
in C++ or optionally in Qt's own markup language QML: Qt Quick, provides a scenegraph associated with the Qt project
in C++, OpenSceneGraph, a 3D graphics API using OpenGL
in C++, the OGRE engine, based on a scene graph, supports multiple scene managers
in C++, OpenSG, a scene-graph system for real-time graphics, with clustering support and multi-thread safety
in C++, the FlightGear Flight Simulator uses a custom Canvas system (LGPL'ed via SimGear) that is hardware-accelerated using OpenSceneGraph/OpenGL, OpenVG/ShivaVG: The FlightGear Canvas system
in Java, the Java FX scene graph with 2D and 3D functionality
in Tcl and other languages such as Perl, Python (Tkinter), and Ruby, the Tk toolkit provides a canvas widget for 2D graphics
in Tcl and other languages such as Perl and Python, TkZinc is an extended replacement for the Tk canvas, which adds support for hierarchical grouping, clipping, affine transformations, anti-aliasing, and specific items for air traffic control.
Some canvas modules within various libraries do not provide the power of a full scene-graph - they operate at a lower level which requires programmers to provide code such as mapping mouse-clicks to objects in the canvas. Examples of 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 Java FX 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
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
Proprietary canvas libraries include, for example:
the Microsoft Windows Win32 Canvas
