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Re: minutes: Canvas sub-group HTML A11y Task Force telecon, 2010-02-15 [draft]

From: James Craig <jcraig@apple.com>
Date: Mon, 15 Feb 2010 18:08:44 -0800
Cc: Richard Schwerdtfeger <schwer@us.ibm.com>, public-canvas-api@w3.org, public-html-a11y@w3.org, david.bolter@gmail.com, David Singer <singer@apple.com>, janina@rednote.net, cooper@w3.org
Message-Id: <4C4D7F67-AECE-493A-935B-99FB7A8B8F70@apple.com>
To: Charles McCathieNevile <chaals@opera.com>
Chaals, those are AUTHOR requirements not UA requirements. The intention is that author's wishing to make canvas accessible are required to visibly draw focus and keyboard cursor position on the canvas. They could do that using an image map as you suggested, or by just changing the style of the canvas-drawn representation of the focused element.

The user setting requirement is trickier, agreed. The only way I thought it might be done today is to set a standard DOM element (perhaps marked with aria-hidden and positioned off screen) to the expected default font size, color, etc. Then have the canvas script check the rendering of that element (getComputedStyle) and use the computed values in the canvas drawing methods. This *should* allow any author to render canvas text in accordance with user prefs such as a user style sheet.

That said, just because it *can* be done, doesn't mean than many authors, if any, will take the time to do that properly.

James



On Feb 15, 2010, at 5:47 PM, Charles McCathieNevile wrote:

> On Mon, 15 Feb 2010 23:59:30 +0100, Richard Schwerdtfeger <schwer@us.ibm.com> wrote:
> 
> ...
>> 20:40:11 [richardschwerdtfe]
>> Authors MUST render visible focus of the ADOM subtree element in the
>> canvas area
>> Authors MUST render visible focus of the canvas subtree element in the
>> canvas area
>> Authors MUST render visible focus of the canvas subtree element on the
>> rendered canvas
> 
> As far as I can tell, by using an image map to represent areas sensitive to user input, all of these things are automatically managed by the User Agent in pretty much every modern user agent (starting with lynx). There is a bug in some versions of Opera which prevents an imagemap inside the canvas from being recognised - this is fixed in current builds of Opera 10.5 and should remain fixed.
> 
>> Authors MUST render the keyboard caret insertion cursor of the canvas
>> subtree element on the rendered canvas
> 
> I'm not sure about handling this one completely automagically, but the use of either forms, or existing editable HTML elements may again provide this easily.
> 
>> 20:42:40 [cyns]
>> authored content SHOULD respond to system settings for font, color and
>> zoom.
>> Authors SHOULD should ensure that the rendered canvas responds to
>> system settings for font, color and zoom
>> Authors SHOULD should ensure that the rendered canvas responds to
>> system settings for font, color and zoom
>> Authors SHOULD should ensure that the rendered canvas responds to
>> system settings for font, color and zoom
>> 20:46:06 [richardschwerdtfe]
>> Define user settings as system, user agent, or web application settings
> 
> This stuff is trickier. We need to describe how the author would find out what those settings are if they are using canvas (although I also need to read up on the canvas text API to make sure I'm not missing something basic).
> 
> cheers
> 
> Chaals
> 
> -- 
> Charles McCathieNevile  Opera Software, Standards Group
>   je parle franšais -- hablo espa˝ol -- jeg lŠrer norsk
> http://my.opera.com/chaals       Try Opera: http://www.opera.com
Received on Tuesday, 16 February 2010 02:09:17 UTC

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