WebAIM - Web Accessibility In Mind

E-mail List Archives

Re: Html5 canvas accessibility

for

From: Joshue O Connor
Date: Mar 25, 2011 4:24AM

Hi Paniz,

> By this sentence:
> "So should you now built stuff that you want to be accessible in <canvas>?
> Nope."
> you mean as a developer,or no as a person who wants to try making canvas
> accessible?

As a developer. Unless you are involved in the spec somehow/browser
manufacturing?

> How can I access the works that has been done on this area?

Check out the links I gave you. There has been good work done in this
area by Steve Faulkner of the Paciello group, Rich Schwerdtfeger IBM,
and Chaals from Opera amongst others.

> And I have a question about IE9,whether it's problem really has been solved?

The problem is the issue is in flux. Also the solution is in flux. That
kinda means that browsers can only implement partial solutions as there
isn't anything definitive for them to implement (if you follow). I
guess, it means the goal posts are constantly moving with this issue.
<canvas> initially didn't have a DOM for example, by design, but the
impact that this would have on a11y wasn't understood at the time, when
people could build UIs/Apps using the <canvas> element. The HTML 5 spec
states, that were there is an accessible alternative to use of the
<canvas> API, this should be used instead. However, developers don't
always follow this kind of advice and the result is potentially, lots of
inaccessible <canvas> widgets/UIs etc on the web. [1]

> Maybe in fact the canvas accessibility is not completely clear for me,
>
> I will be thankful if any body explain it's problem in a sentence,because I
> dizzy,in some blog post for 2009 I read that the problem is about fallback
> content,that it seems by release of IE9 it has been solved:(

No, its not solved. The problem is that <canvas> is entirely a pixel
based drawing surface. This means that there is no support for any kind
of semantics which we usually use to create accessible content on the
web. In practice, this means that Assistive Technology cannot talk (as
such) to the code under the hood to understand the underlying structure
of images/elements etc that are drawn onto the <canvas> element.

Now, that's an overview of the issue. However, there has been some
progress with allowing a DOM to be created (or in other words an
Accessibility Tree, or nodes for semantic content that will allow AT to
understand whats there to some degree) and support for children of the
element and/or fallback content.

There is a lot of discussion about how this fallback content is to be
handled and how the various roles etc of this content is to be parsed by
AT. This is certainly still in flux, or up in the air.

I hope this helps and doesn't confuse further. In truth, its not an easy
issue to understand but there is some progress and its good to see IE 9
support the model of accessible fallback content for the <canvas> element.

Cheers

Josh

[1] http://dev.w3.org/html5/spec/the-canvas-element.html

NCBI: Celebrating 80 Years

********************************************************************
National Council for the Blind of Ireland (NCBI) is a company
limited by guarantee (registered in Ireland No. 26293) .
Our registered office is at Whitworth Road, Drumcondra, Dublin 9.
NCBI is also a registered Charity (chy4626).

NOTICE: The information contained in this email and any attachments
is confidential and may be privileged. If you are not the intended
recipient you should not use, disclose, distribute or copy any of
the content of it or of any attachment; you are requested to notify
the sender immediately of your receipt of the email and then to
delete it and any attachments from your system.

NCBI endeavours to ensure that emails and any attachments generated
by its staff are free from viruses or other contaminants. However,
it cannot accept any responsibility for any such which are
transmitted. We therefore recommend you scan all attachments.

Please note that the statements and views expressed in this email
and any attachments are those of the author and do not necessarily
represent the views of NCBI


********************************************************************