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RE: The Canvas 2D API 1.0 Specification

From: Jim Allan <jimallan@tsbvi.edu>
Date: Wed, 19 Aug 2009 12:53:52 -0500
To: "'Simon Harper'" <simon.harper@manchester.ac.uk>, "'UAWG list'" <w3c-wai-ua@w3.org>
Message-ID: <08f201ca20f6$057be610$1073b230$@edu>
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 Wednesday, 19 August 2009 17:58:35 GMT

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