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[Bug 7011] canvas accessible fallback provison is under specified

From: <bugzilla@wiggum.w3.org>
Date: Fri, 26 Jun 2009 08:49:41 +0000
To: public-html-bugzilla@w3.org
Message-Id: <E1MK77t-0004xP-RS@wiggum.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=7011





--- Comment #2 from Ian 'Hixie' Hickson <ian@hixie.ch>  2009-06-26 08:49:41 ---
(from the cited blog post:)

* Text in canvas

There is a native method to display text in canvas (example of its use:
Cufón), but no native method to output text as fallback. So the developer
using canvas to replace text either needs to implement a method using scripting
or manually add the fallback text.

It is suggested that to make it practical for developers to provide fallback
for disabled users who cannot access the text content directly, a native method
that outputs the text as fallback is added to the canvas API.


* Images in canvas

There is a native method for inserting images into canvas (Example of its use:
Canvas Slideshow (with HTML5 canvas), but no methods to add a text alternative
to the images or method to output such images as fallback. So the developer
using images in canvas either needs to implement a method using scripting or
manually add the fallback images and text alternatives.

It is suggested that to make it practical for developers to provide fallback
for disabled users who cannot access the image content directly a native method
that allows the addition of text alternatives and an output method that inserts
img elements as fallback content, is added to the canvas API.


* User interface elements in canvas

canvas can be used to create interactive interfaces (example of its use:
bespin), but there are no methods to assign roles, states and properties to
areas of a canvas that represent widgets, controls or links. So the developer
who wants to create an accessible interface has to duplicate the content of the
canvas interface using HTML elements that provide native roles, states and
properties.

It is suggested that to make it practical for developers to provide information
about UI elements to disabled users who cannot access information visually,
native methods be provided that allow for the identification of the roles,
states and properties of user interface elements displayed on a canvas,
futhermore a method to define discrete focusable areas of the canvas be
provided.

A crude example of some of the features required in canvas can be illustrated
using a HTML image map. The example uses a canvas pie menu demonstration by Ben
Galbraith to which a transparent image map has been added. The image map
provides  keyboard access to segments of the pie menu, it also provides
information about their role and state of each and name (text alternative) for
each segment. Note: Use of this image map technique, while useful for
illustrative purposes is not proposed as a practical solution.


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Received on Friday, 26 June 2009 08:49:50 GMT

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