Re: Please vote on the canvas accessibility proposal

Rich Schwerdtfeger
Distinguished Engineer, SWG Accessibility Architect/Strategist

Ian Hickson <ian@hixie.ch> wrote on 02/24/2010 03:32:21 PM:

> Ian Hickson <ian@hixie.ch>
> 02/24/2010 03:32 PM
>
> To
>
> Richard Schwerdtfeger/Austin/IBM@IBMUS
>
> cc
>
> public-canvas-api@w3.org, "public-html-a11y@w3.org"
<public-html-a11y@w3.org>
>
> Subject
>
> Re: Please vote on the canvas accessibility proposal
>
> On Wed, 24 Feb 2010, Richard Schwerdtfeger wrote:
> >
> > > # "When authors use the canvas element, they must also provide
content
> > > # that, when presented to the user, conveys essentially the same
> > > # function or purpose as the bitmap canvas."
> >
> > That is not an RFC MUST.
>
> It is a normative conformance requirement with the full weight of RFC
2119
> behind it, if that's what you mean.
>
>
> > It also does not mean it is accessible if you are saying the canvas can

> > only act as a bitmap.
>
> I don't see how something that "conveys essentially the same function or
> purpose", when presented to the user, can be anything _but_ accessible.
>
You are saying that it has the same function as the "bitmap" canvas. I read
this as having the function of a bitmap.
Also, fallback content could provide similar function (essentially the
same) but that does not mean the same function of the canvas as it is
rendered.

So, if what you are saying is true most or a vast majority of canvas
implementations are in non-compliance.

>
> This is the same kind of requirement as we have for <img alt=""> ("the
alt
> attribute [...] must convey the same message as the image specified in
the
> src attribute", and so forth -- there's a whole huge section giving all
> the requirements for <img alt> being accessible).
>

img alt is the most simplistic example and only conveys the text equivalent
aspect of accessibility. If you know <canvas> behaves like an image or
bitmap then that would be a good start. If you go to something like bespin,
which is not a bitmap then we have a problem. Perhaps we are arguing
semantics but clearly the current wording has not helped to promote
accessible canvas development.


> --
> Ian Hickson               U+1047E                )\._.,--....,'``.    fL
> http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
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