W3C home > Mailing lists > Public > public-html-a11y@w3.org > June 2011

Re: hit testing and retained graphics

From: Richard Schwerdtfeger <schwer@us.ibm.com>
Date: Fri, 24 Jun 2011 14:26:33 -0500
To: "Edward O'Connor" <eoconnor@apple.com>
Cc: public-canvas-api@w3.org, public-html@w3.org, public-html-a11y@w3.org, public-html-request@w3.org, jbrewer@w3.org
Message-ID: <OF78083369.CD5FFD5A-ON862578B9.0066F482-862578B9.006ACCCE@us.ibm.com>


So, one could interpret your statements that Apple and Webkit developers
(this includes Google) support leaving canvas inaccessible to people with

If that is not true, what is your alternative proposal to fill the gap
regarding not being able to provide the bounds of a drawing object to an
assistive technology?

We are only a few steps away from completing the gaps in canvas
accessibility. It would be a very sad situation to prohibit access to
canvas applications by people with disabilities simply because the browser
manufacturers - Apple, Google, and Microsoft are unwilling to address the
problem. At the end of the day, a user with a disability could care less if
Apple likes retained mode graphics in canvas or not. They just want to be
able to do the same tasks the rest of us do.

So, if you exclude retained mode graphics features, here are the options
that are on the table Edward:

- apply an image map that an author must maintain on top of canvas. This
means the authors must maintain and process the transformations on all the
coordinates and associate the coordinates with an object in the shadow DOM.
- Write paths into the canvas subtree elements and maintain them as well as
the transformations of the coordinates.
- Do absolutely nothing and state that canvas will be inaccessible from
here on out.

What is Apple and Webkit member's solution to the problem.

Up to now Webkit developers, and that includes Apple, have created canvas
without any consideration to accessibility, much the way retained mode
graphics were not addressed, and we are a few steps away from fixing it. Is
this how you want to leave it?


Rich Schwerdtfeger
CTO Accessibility Software Group

From:	"Edward O'Connor" <eoconnor@apple.com>
To:	public-html@w3.org
Cc:	public-canvas-api@w3.org, public-html-a11y@w3.org
Date:	06/24/2011 01:20 PM
Subject:	Re: hit testing and retained graphics
Sent by:	public-html-request@w3.org


I've talked with several WebKit engineers here at Apple, including those
who invented <canvas>, and the consensus is that adding retained-mode
features to the Canvas API is not something we're interested in.

The Canvas API is an immediate-mode graphics API. Essentially, it's a
programmable <img>. If you want to do hit testing you have to implement
it yourself, by tracking what you draw. Grafting random pieces of a
retained-mode API into it is bad design. Like folk from Google[1] and
Microsoft[2] have pointed out, the Web's retained-mode graphics feature
is SVG.

> I have a very large IBM application in development and given the state
> of SVG accessibility and how the application is constructed it is not
> a good fit.

If there are accessibility problems with SVG, we should let the SVG WG
know about the problems so that they can be fixed. If existing SVG
implementations aren't performant enough for your use cases, please file
bugs on those implementations.


1. http://lists.w3.org/Archives/Public/public-html/2011Jun/0339.html
2. http://lists.w3.org/Archives/Public/public-html/2011Jun/0351.html

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Received on Friday, 24 June 2011 19:27:54 UTC

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