Re: Proposal: Canvas accessibility and a media querries approach for alternative content (Action Item 6 in the HTML Accessibility Task Force)

Rich Schwerdtfeger
Distinguished Engineer, SWG Accessibility Architect/Strategist

public-canvas-api-request@w3.org wrote on 01/20/2010 06:39:19 AM:

> Maciej Stachowiak <mjs@apple.com> 
> Sent by: public-canvas-api-request@w3.org
> 
> 01/20/2010 06:39 AM
> 
> To
> 
> Steven Faulkner <faulkner.steve@gmail.com>
> 
> cc
> 
> Ian Hickson <ian@hixie.ch>, public-canvas-api@w3.org, HTML WG 
> <public-html@w3.org>
> 
> Subject
> 
> Re: Proposal: Canvas accessibility and a media querries approach for
> alternative content (Action Item 6 in the HTML Accessibility Task Force)
> 
> 
> On Jan 20, 2010, at 4:21 AM, Steven Faulkner wrote:
> 
> > Hi Ian,
> > 
> > >The click fires on the <canvas>, and the script is responsible for
> > >propagating the click to the link to cause the navigation (the UA has 
no
> > >idea that it corresponds to the <a>, so it can't happen 
automatically).
> > 
> > so if the script propagates the click to the link element, it 
> would seem that the content of the canvas element should no longer 
> be considered 'fallback' as interaction and resulting actions are 
> routed through the a element in the canavas element for all users 
> not only those with disabilites.
> 
> If you're using the contained DOM children as a model/controller in 
> this way, then indeed, it's not just 'fallback'. It becomes a way of
> building your application logic in a way that also makes it very 
> easy to expose to assistive technologies. Doing it that way is an 
> option, however, not a technical requirement. You could just as 
> easily just assign window.location to navigate, in this example.
> 
> > 
> > >On the other hand, if the user hits enter while the link is focused, 
the
> > >event goes to the link and the UA does the navigation automatically.
> > 
> > so if the link is focused and the user clicks on the region within
> the focus rectangle then the click will pass to the link without the
> need for the script?
> 
> According to what Ian said, that won't happen. 
> 
> Furthermore, objects in a canvas need not be rectangular and in 
> general can be all sorts of funny shapes. While a rectangle might be
> the best approximation we can do for focus purposes, it would not be
> appropriate to force that restriction for hit testing. Not only 
> that, but visual objects in the canvas can stack, and knowing their 
> focus rectangles alone does not tell you the z-order, so even hit 
> testing of purely rectangular objects might not work right (z-order 
> might not match logical order and therefore might not be the order 
> in which things appear in the hidden/fallback/model DOM.

Yes, both are true. The script for processing the canvas must manipulate 
the shadow DOM and perform the actions. That is fine.

> 
> Regards,
> Maciej
> 
>