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RE: The Canvas 2D API 1.0 Specification

From: Jim Allan <jimallan@tsbvi.edu>
Date: Thu, 20 Aug 2009 09:11:11 -0500
To: "'Simon Harper'" <simon.harper@manchester.ac.uk>
Cc: "'UAWG list'" <w3c-wai-ua@w3.org>
Message-ID: <09cd01ca21a0$12551410$36ff3c30$@edu>
PF is already on this. Interestingly, HTML5 is as much a specification for
designing a user agent as it is a language spec. Viewed in that light, it
could prove useful to UAWG as a jumping off point for filling-in
accessibility gaps. One area to fill in would be the notion of fallback
content. The user should have access to the fallback regardless of the state
of the parent element. In other words, the user should have access to the
fallback content whether canvas scripting is on or off, or other conditions.

The question becomes, will UA developers actually implement these items.
Canvas will still work even if the user has no access to the fallback
content. This is the status quo with 'objects' now (Flash, video players,
etc.). They all function, yet the user has no easy access to fallback
content.

Jim

> -----Original Message-----
> From: w3c-wai-ua-request@w3.org [mailto:w3c-wai-ua-request@w3.org] On
Behalf
> Of Simon Harper
> Sent: Thursday, August 20, 2009 3:10 AM
> To: Jim Allan
> Cc: 'UAWG list'
> Subject: Re: The Canvas 2D API 1.0 Specification
> 
> It seems then that the accessibility interface to canvas is the bit
> we should be working on as canvas seems like a mini-ua? We should
> start to make suggestions and give solutions to the html5 people IMO.
> 
> 
> Cheers
> Si.
> 
> =======================
> 
> Simon Harper
> University of Manchester (UK)
> 
> Human Centred Web Lab: http://hcw.cs.manchester.ac.uk
> 
> My Site: http://hcw.cs.manchester.ac.uk/people/harper/
> 
> My Diary (Web): http://hcw.cs.manchester.ac.uk/people/harper/
> phpicalendar/week.php
> My Diary (Subscribe): http://hcw.cs.manchester.ac.uk/diaries/harper/
> SimonHarper.ics
> 
> 
> 
> 
> 
> On 19 Aug 2009, at 18:53, Jim Allan wrote:
> 
> > Thanks Simon. It's a nice statement. We all know, if a developer
> > can do
> > something they will.
> >
> > One troubling bit is
> >> When authors use the canvas interface element, they must also provide
> >> content that, when presented to the user, conveys essentially the
> >> same function or purpose as the bitmap canvas. This content may be
> >> placed as content of the canvas interface element. The contents of
> >> the canvas interface element, if any, are the element's fallback
> >> content.
> >
> > UAAG20 has
> > 3.1.1 Notification of Alternative Content: Provide a global option
> > for the
> > user to be notified of alternatives to rendered content (e.g.,
> > short text
> > alternatives, long descriptions, captions).
> >
> > 3.1.2 Configurable Default Rendering: Provide the user with the global
> > option to set which type of alternative to render by default. If the
> > alternative content has a different height and/or width, then the
> > user agent
> > will reflow the viewport. (Level A)
> >
> > We had similar stuff in UAAG10. However no User Agents have yet
> > implemented
> > a way to easily get to the internal element "fall back content".
> >
> > Another troubling item is
> >> In interactive visual media, if scripting is enabled for the canvas
> >> interface element, the canvas interface element represents an
> >> embedded element with a dynamically created image.
> >
> > This implies there is separate scripting for canvas. Separate from
> > javascript? A different instance? How does a user (or agent) turn off
> > scripting for just canvas?
> >
> > Jim
> >
> >> -----Original Message-----
> >> From: w3c-wai-ua-request@w3.org [mailto:w3c-wai-ua-request@w3.org] On
> > Behalf
> >> Of Simon Harper
> >> Sent: Wednesday, August 19, 2009 10:46 AM
> >> To: UAWG list
> >> Subject: The Canvas 2D API 1.0 Specification
> >>
> >> I was monitoring xtech and saw this going through
> >>
> >> http://dev.w3.org/html5/canvas-api/canvas-2d-api.html
> >>
> >>
> >> which says..
> >>
> >> 5. Accessibility Considerations
> >>
> >> Authors should not use the canvas interface element in a document
> >> when a more suitable element is available. For example, it is
> >> inappropriate to use a canvas interface element to render a page
> >> heading: if the desired presentation of the heading is graphically
> >> intense, it should be marked up using appropriate elements (typically
> >> h1) and then styled using CSS and supporting technologies such as
> >> XBL.
> >>
> >> When authors use the canvas interface element, they must also provide
> >> content that, when presented to the user, conveys essentially the
> >> same function or purpose as the bitmap canvas. This content may be
> >> placed as content of the canvas interface element. The contents of
> >> the canvas interface element, if any, are the element's fallback
> >> content.
> >>
> >> In interactive visual media, if scripting is enabled for the canvas
> >> interface element, the canvas interface element represents an
> >> embedded element with a dynamically created image.
> >>
> >> In non-interactive, static, visual media, if the canvas interface
> >> element has been previously painted on (e.g. if the page was viewed
> >> in an interactive visual medium and is now being printed, or if some
> >> script that ran during the page layout process painted on the
> >> element), then the canvas interface element represents embedded
> >> content with the current image and size. Otherwise, the element
> >> represents its fallback content instead.
> >>
> >> In non-visual media, and in visual media if scripting is disabled for
> >> the canvas interface element, the canvas interface element represents
> >> its fallback content instead.
> >>
> >>
> >>
> >> they say...
> >>
> >> Techniques and additional APIs to make specific uses of canvas
> >> interface elements more widely accessible are under discussion, and
> >> will be reflected in this draft as progress is made.
> >>
> >> I wonder what these are?
> >>
> >>
> >> Cheers
> >> Si.
> >>
> >> =======================
> >>
> >> Simon Harper
> >> University of Manchester (UK)
> >>
> >> Human Centred Web Lab: http://hcw.cs.manchester.ac.uk
> >>
> >> My Site: http://hcw.cs.manchester.ac.uk/people/harper/
> >>
> >> My Diary (Web): http://hcw.cs.manchester.ac.uk/people/harper/
> >> phpicalendar/week.php
> >> My Diary (Subscribe): http://hcw.cs.manchester.ac.uk/diaries/harper/
> >> SimonHarper.ics
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> 
Received on Thursday, 20 August 2009 14:15:33 GMT

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