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Re: Content positioning in Canvas fallback content feedback requested

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 25 Feb 2011 14:53:25 -0800
Message-ID: <AANLkTikAcq5PgSTHYBRBywOXZFY7bkQZB05D56P2wG-9@mail.gmail.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
Cc: public-html@w3.org, public-html-a11y@w3.org, franko@microsoft.com, chuck@jumis.com, david.bolter@gmail.com
On Fri, Feb 25, 2011 at 2:23 PM, Richard Schwerdtfeger
<schwer@us.ibm.com> wrote:
> One of the features that platform accessibility API have is bounding
> rectangles associated with accessible objects. Screen magnifiers use this
> information to allow the user to zoom to an arbitrary, visual object in
> view. AI Squared has asked that we provide this feature for the fallback
> content such that fallback content objects can be positioned, with
> dimensions relative to where they are drawn on the physical <canvas>.
> There are a couple of ways we see this can be done:
> - apply shape and coords similar to image maps in fallback content
> - Parially, using CSS positioning.
> We have wrestling with how best to do this as it is expensive for
> developers. We would like to hear what members think would be the preferred
> way to address this issue. What would people prefer? Is there an alternative
> that would be better?
> To produce an accessible canvas there is a one for one correspondence
> between elements in fallback content and what is drawn on the canvas, i.e.
> if there is a checkbox drawn on canvas there would be an associated checkbox
> in fallback content. Now we just need a way to have the fallback content
> reflect the position and dimensions as best possible.

While canvas descendants aren't rendered, they are exposed to CSS, and
can thus be styled (the styling just won't have any visual effect,
since they're not rendered no matter what you do).

So, you can just use normal CSS positioning to keep the fallback
content in sync with the visual position of things on the canvas.

Received on Friday, 25 February 2011 22:54:18 UTC

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