Canvas

The canvas element is part of HTML 5 and allows for dynamic scriptable rendering of bitmap images.

It was initially introduced by Apple for use inside their own Mac OS X WebKit component, powering applications like Dashboard widgets and the Safari browser. Later, it was adopted by Gecko browsers and Opera^[1] and standardized by the WHATWG on new proposed specifications for next generation web technologies. Novell manufactures an XForms processor plugin for Internet Explorer, which also provides support for the canvas element.^[2] Independent efforts exist to support the canvas feature on Internet Explorer that do not require plugins and are based solely on VML and JavaScript.^[3] Google has also begun a project to add canvas abilities to Internet Explorer using the same techniques.^[4]

Canvas consists of a drawable region defined in HTML code with height and width attributes. JavaScript code may access the area through a full set of drawing functions similar to other common 2D APIs, thus allowing for dynamically generated graphics. Some anticipated uses of the canvas include building graphs, animations, games, and image composition.

Reactions

At the time of its introduction the canvas element met with mixed reactions from the web standards community. There have been arguments against Apple's decision to create a new proprietary element instead of supporting the SVG standard. Further arguments are concerning the logic upon which canvas was conceived: being completely procedural and not having a descriptive counterpart allowed canvas to 'paint', but drawn elements are not identifiable in a DOM-like way. Other concerns, not about the proprietary extension per se, but in regard to the proposed syntax for those elements. For example, they consider the absence of a namespace indication to be undesirable.^[5]

Intellectual property over canvas

On March 14, 2007, WebKit developer Dave Hyatt forwarded an email from Apple's Senior Patent Counsel, Helene Plotka Workman^[6], which stated that Apple reserved all intellectual property rights relative to WHATWG’s Web Applications 1.0 Working Draft, dated March 24, 2005, Section 10.1, entitled “Graphics: The bitmap canvas” (sic)^[7], but left the door open to licensing the patents should the specification be transferred to a standards body with a formal patent policy. This caused considerable discussion among web developers, and raised questions concerning the WHATWG's lack of a policy on patents in comparison to the W3C's explicit favoring of royalty-free licenses. Apple later disclosed the patents under the W3C's royalty-free patent licensing terms.^[8] The disclosure means that Apple is required to provide royalty-free licensing for the patent whenever the Canvas element becomes part of a future W3C recommendation created by the HTML working group.^[9]

See also

• SVG
• Quartz (graphics layer)
• GDI+
• Cairo (graphics)
• Comparison of layout engines (HTML 5)
• Wii Opera SDK / HullBreach SDK - JavaScript 3D canvas library

References

1. ^ Opera 9.0 changelog
2. ^ Novell XForms Explorer
3. ^ Canvas in IE
4. ^ Google's Canvas in IE project
5. ^ Ian Hickson remarks regarding canvas and other Apple extensions to HTML
6. ^ [whatwg] Web Applications 1.0 Draft, David Hyatt, Wed Mar 14 14:31:53 PDT 2007
7. ^ Web Applications 1.0 Early Working Draft - Dynamic graphics: The bitmap canvas
8. ^ HTML Working Group Patent Policy Status – Known Disclosures
9. ^ W3C patent policy in use by HTML working group

External links

• Canvas description in WHATWG Web Applications draft specifications
• Canvas reference page in Apple Developers Connection
• Basic Canvas Tutorial on Opera Developer Community
• Canvas tutorial and introductory page on Mozilla Developer center
• Canvas Demos A comprehensive list of demos, tutorials and tools for the canvas element.
• Wii Opera SDK 3D Canvas Library for Internet Gaming
• An interactive blob Test your browser.
• Canvas example using Gnuplot driver
• w3 html5 canvas element
• w3 html5 canvas 2d methods