Fwd: Re: Issue 13176 - Justification / Examples

Apologies, all,
I should have e-mailed the following through public-canvas-api.

-Charles

-------- Original Message --------
Subject: 	Re: Issue 13176 - Justification / Examples
Date: 	Thu, 28 Jul 2011 13:04:55 -0700
From: 	James Robinson <jamesr@google.com>
To: 	Charles Pritchard <chuck@jumis.com>
CC: 	Simetrical+w3c@gmail.com, timeless <timeless@gmail.com>, Cameron 
McCormack <cam@mcc.id.au>



Please email lists, don't email me directly.

On Thu, Jul 28, 2011 at 12:58 PM, Charles Pritchard <chuck@jumis.com 
<mailto:chuck@jumis.com>> wrote:

    For issue:
    http://www.w3.org/Bugs/Public/show_bug.cgi?id=13176#c5

    "Use Cases"
    http://www.w3.org/WAI/PF/HTML/wiki/Canvas_Accessibility_Use_Cases
    http://wiki.whatwg.org/wiki/Active_Image_Accessibility_Use-cases

    Supporting:
    "GetBoundsRect"
    http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility.cc?revision=64943&view=markup&pathrev=72440
    <http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility.cc?revision=64943&view=markup&pathrev=72440>
    Used by:
    http://msdn.microsoft.com/en-us/library/accessibility.iaccessible.acclocation.aspx
    "STDMETHODIMP BrowserAccessibilityWin::accLocation"
    http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility_win.cc?revision=72440&view=markup&pathrev=72440
    <http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility_win.cc?revision=72440&view=markup&pathrev=72440>
    <http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility_win.cc?revision=72440&view=markup&pathrev=72440
    <http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/accessibility/browser_accessibility_win.cc?revision=72440&view=markup&pathrev=72440>>

    Example:
    http://w115.visc.us/darkroom-live/dist/
    The top bar is drawn in canvas: the top right of the screen has
    several buttons,
    "Help is on", is one of those buttons. You may mouse over the
    button, a title appears.

    Those buttons can not work fully with ZoomText nor do they work with
    Apple's VoiceOver for Mobile Safari.

    An AT such as ZoomText may allow the user to cycle through all
    "button" elements on a page,
    moving each into the viewable area, but not sending focus until the
    user makes a further action.

    An AT such as VoiceOver for Mobile Safari allows a user to drag
    their finger across a screen,
    and instead of sending mousemove and mousedown events, it simply
    looks up bounding
    boxes from the accessibility tree (IAccessible, essentially). When
    the user double-taps
    the screen, then a focus event is setup and the element is activated.

    Neither of these ATs work well with <canvas><button tabIndex
    /></canvas>, because
    the IAccessible tree is not populated with bounds information.

    Whether called "setClickableRegion(<button tabIndex / >)" or
    setElementPath,
    or any other name, we need a method to have the Canvas2d implementation
    send the current bounds to the Browser Accessibility implementation
    for the specified element.

    Does this help the three of you understand the issue? Would a phone
    call help? Is there
    anything I can do to further explain or illustrate the bounds-based
    issue I'm encountering with AT software?

    I'm responding, the best I can, to your seeming request on IRC for
    more information:
    http://krijnhoetmer.nl/irc-logs/whatwg/20110728#l-53

    Please consider my willingness to put time into this issue as a sign
    of its importance to me.
    My discussion with Tab Atkins about "correct" uses of Canvas is an
    unfortunate
    diversion from a very simple technical issue.

    -Charles