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Review of Ian's changes for path

From: Richard Schwerdtfeger <schwer@us.ibm.com>
Date: Tue, 20 Mar 2012 16:27:31 -0500
To: public-html-a11y@w3.org
Cc: jbrewer@w3.org, chuck@jumis.com, "Frank Olivier" <Frank.Olivier@microsoft.com>, cyns@exchange.microsoft.com, janina@rednote.net, david.bolter@gmail.com, faulkner.steve@gmail.com
Message-ID: <OFD08303E9.59FEA0D5-ON862579C7.006F6FD7-862579C7.0075E079@us.ibm.com>


I was asked to review Ian's changes to the canvas 2D Context API and its
impact on the accessibility issue for magnifiers, hit testing, and Frank
Olivier's proposal:

1. Ian's change was only to introduce SVG's path functionality to Canvas.
Standing on its own it does not address Issue-201
(http://www.w3.org/html/wg/tracker/issues/201) for supporting canvas hit
testing and providing location information to assistive technologies. I
don't know if an issue was logged to provide SVG Path support but it was
discussed on the list.
2. His proposal is part of a collection of changes that Ian is working on
that would impact these accessibility defects:
http://wiki.whatwg.org/wiki/Canvas
As I may have mentioned Steve Faulkner and I have been providing use cases
to Ian and feedback on work he is doing to address Issue-201. You can see
some of that on this page. That said, Ian has not made a direct change to
the W3C spec. to address our defects nor has he submitted a change proposal
to the working group for a new function addHitRegion().

That said, the change does impact Frank's proposal
(http://www.w3.org/wiki/Canvas_hit_testing) and the work being done on the
link, if submitted, would introduce a new web MVC mechanism to the Web that
either non-WebKit-based or non-Chrome browsers does not support today. That
would have accessibility implications. I will elaborate:

1. Frank's proposal assumed the using the current canvas path. Ian has
introduced an entirely new path mechanism, that is a bit heavy weight, that
was not there before. Frank's proposal would need to change to accommodate
it, yet Frank stated Microsoft would not support it. - a conundrum.
2. When I was at TPAC a Google developer showed me new work he was doing on
a new MVC model for the Web, similar to XBL, with a new model that could be
bound to different rendering engines: SVG, Canvas, etc. This object model
is separate from the DOM and I was told that this recently went into a
Chrome trunk. The addHitRegion() function would allow for access to a
separate model in that the element parameter is not required (See Ian's
comments). None of the ATs, including Google Chrome make use of it today so
introducing this mechanism would require a comprehensive accessibility
effort as it is a DOM circumvention. Please read my comments on
addHitRegion.

Rich

Rich Schwerdtfeger
Received on Tuesday, 20 March 2012 21:28:55 UTC

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