RE: Draft Revisions to Canvas 2D Context API

It is possible for a magnifier to follow the focus; the built-in Windows 7 magnifier is an example of this (the option is not enabled by default).

From: Richard Schwerdtfeger [mailto:schwer@us.ibm.com]
Sent: Sunday, April 11, 2010 4:50 PM
To: Frank Olivier; Janina Sajka; public-canvas-api@w3.org; Steven Faulkner; public-html-a11y@w3.org; david.bolter@gmail.com
Subject: Draft Revisions to Canvas 2D Context API


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