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Re: Draft Revisions to Canvas 2D Context API to drive magnification

From: James Craig <jcraig@apple.com>
Date: Thu, 20 May 2010 15:31:44 -0700
Cc: public-canvas-api@w3.org, public-html-a11y@w3.org
Message-Id: <7FE190CA-87DC-400B-AD23-A2DC5EA779B6@apple.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
There is a way for Zoom to follow focus/caret position that could be implemented for this proposal. We're looking into how much effort this would involve for WebKit, but I don't have anything to report on that now.

Initial feedback for the proposed methods:

1. The focus ring should be a set of coordinates or a shape rather than a single xy coordinate. At a minimum, it should be rect(x1, y1, x2, y2), but it'd be better to use a standard shape as the parameter, e.g. line, rectangle, ellipse, or polygon... Poly would allow not only non-standard shapes, but would also provide an easy way to implement focus rings for UI elements that appear skewed or rotated.

2. Caret position should likewise have more than one coordinate or shape(s), especially since I assume this is intended to work for both selection ranges as well as unselected caret position. Perhaps a some optional parameters such as cursor type (I-beam, block, etc.), orientation (vertical, horizontal LTR, horizontal RTL), and maybe language/locale (Are there any language- or locale-specific cursors? I don't know.)




On Apr 29, 2010, at 2:25 PM, Richard Schwerdtfeger wrote:

> Hi Maciej, 
> 
> I have not heard back from Apple on this proposal. Please take a look at the proposal (attached HTML file) and let me know if this will work for the Mac. I think I addressed your issues and would like your feedback. 
> 
> We have an MSAA API call on Windows which we can call to set the Caret Position so that a magnifier can can follow it which can be used by IE and FF. 
> 
> I don't know if you have a similar API for the Mac where the selection position could drive the magnifier.
> 
> Thanks,
> 
> Rich
> 
> 
> 
> Rich Schwerdtfeger
> CTO Accessibility Software Group
> ----- Forwarded by Richard Schwerdtfeger/Austin/IBM on 04/29/2010 04:17 PM -----
> 
> Richard Schwerdtfeger/Austin/IBM@IBMUS 
> Sent by: public-canvas-api-request@w3.org
> 04/11/2010 06:49 PM
> 
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> To
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> 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, david.bolter@gmail.com
> <ecblank.gif>
> cc
> <ecblank.gif>
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> Subject
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> Draft Revisions to Canvas 2D Context API
> <ecblank.gif>	<ecblank.gif>
> 
> 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.
> 
> 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(See attached file: 2dcontext10-Apr-11.html)
> 
> <2dcontext10-Apr-11.html>
Received on Thursday, 20 May 2010 22:32:18 UTC

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