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Re: Draft Revisions to Canvas 2D Context API

From: David Bolter <david.bolter@gmail.com>
Date: Thu, 29 Apr 2010 13:07:26 -0400
Message-ID: <4BD9BCCE.5000309@gmail.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
CC: Frank Olivier <franko@microsoft.com>, Janina Sajka <janina@rednote.net>, "public-canvas-api@w3.org" <public-canvas-api@w3.org>, Steven Faulkner <faulkner.steve@gmail.com>, public-html-a11y@w3.org
Hi Rich,

I'm sorry this email got lost in my stack! I've replied to the part 
directed at me below:

On 11/04/10 7:49 PM, Richard Schwerdtfeger wrote:
>
> Sorry it took so long for me  to get this draft out. Too much traveling
> going on. Please take a look and provide feedback.
>
> The edits reflect:
>
> - Separate caret/selection from drawFocusRing
> http://lists.w3.org/Archives/Public/public-html/2010Mar/0502.html. The Mac
> does not support caret tracking during selection so this needed to be
> allotted for.
> - Expose the caret blink rate via 2D canvas API. Frank indicated Windows
> has a 500 millisecond defult blink rate a. Carl Carlson (Apple) indicated a
> default blink rate of 560 milliseconds. I provided information for authors
> regarding average default blink rates should the value returned be negative
> 1.
> - Change the name of canDrawCustom and clean up its definiton which
> according to Maciej is "want to draw custom unless Special Focus Ring
> Setting is in Effect"
> http://lists.w3.org/Archives/Public/public-html/2010Mar/0363.html
>
>
> David Bolter: From the Firefox perspective we still need to see that the
> caret/selection location can be properly mapped to the accessibility API as
> is. Currently, the caret position is a logical one in IA2 and I believe the
> caret pixel position is calculated from the character font offset and the
> bounding rectangle of the text. We may need to move the system caret. I am
> trying to find the old Windows API for that.
>    

On Windows FF updates the system caret when focus changes or when the 
caret offset changes. We call such Windows functions as:
CreateCaret 
(http://msdn.microsoft.com/en-us/library/ms648399%28VS.85%29.aspx)
ShowCaret
SetCaretPos

I hope that helps. I didn't test this via AT.

cheers,
David

> Frank: Please see if we can map the pixel position accurately, when
> provided, from the accessibility API. Windows used to have an MSAA
> notification for driving a  magnifier based on screen position. I don't
> know if this is still used when using UIA Express.
>
> Maciej or James: Same question for Mac regarding the caret/selection
> position.
>
> (See attached file: 2dcontext10-Apr-11.html)
>
> Rich Schwerdtfeger
> CTO Accessibility Software Group
>    
Received on Thursday, 29 April 2010 17:08:08 GMT

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