W3C home > Mailing lists > Public > public-html@w3.org > November 2007

Re: SURVEY: Accept requirement for immediate mode graphics a la canvas element?

From: James Graham <jg307@cam.ac.uk>
Date: Fri, 30 Nov 2007 14:15:11 +0000
Message-ID: <47501AEF.4050503@cam.ac.uk>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
CC: Anne van Kesteren <annevk@opera.com>, HTML WG <public-html@w3.org>, public-html-request@w3.org

Richard Schwerdtfeger wrote:
> James,
> Sure. In a broader view - yes <img> would have the same problem except for
> the fact that images have been captured from a a variety of means (camera,
> etc.) where we have no opportunity to provide the semantics other than
> possibly a longdesc or alt text.
> Let's take SVG or ODF Drawings for example. With these I can apply a
> properties on the markup that describes defines the object and its state.
> The markup get converted to a DOM which I can access and expose through a
> API.
> <svg:group role="menuitem" title="launch application">
> With Canvas you draw and and it goes into the bit bucket. There is noway to
> capture and access the semantics of what you are doing.

Sure there is; you can add it as child nodes to the <canvas> element. So, for 
the menu example above you could use markup like:
<ul><li><a href="">Launch Application</a></li></ul>
or alternatively add the fallback as part of the script. As for whether authors 
will bother to provide such fallback; I would expect the same subset of 
developers who are accessibility-aware to make the required effort for <canvas> 
as for <svg>.

> With a fallback, I may have a text alternative for say a map which is a set
> of directions. This is fine for someone who is blind. For someone with a
> cognitive impairment I may need something else.

I don't dispute this at all, but it seems like it would be equally true if the 
page originally had no map and was just a page of textual driving instructions. 
So this argument applies equally to, say, <p> as to <canvas> or <img>.

>    One alternative does not fit all even though a fallback may be an
>    improvement for some.
>    I am concerned that we would advocate using canvas over SVG where we
>    would have an opportunity to apply semantics to the base drawing,

I don't think we would advocate <canvas> where a more appropriate technology 
exists, only where it makes sense.

"Eternity's a terrible thought. I mean, where's it all going to end?"
  -- Tom Stoppard, Rosencrantz and Guildenstern are Dead
Received on Friday, 30 November 2007 14:15:50 UTC

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