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Re: feedback requested: Canvas change for improved hit testing that also facilitates accessibility

From: Charles Pritchard <chuck@jumis.com>
Date: Fri, 01 Apr 2011 14:59:11 -0700
Message-ID: <4D964AAF.6040303@jumis.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
CC: Boris Zbarsky <bzbarsky@mit.edu>, "cyns@exchange.microsoft.com" <cyns@exchange.microsoft.com>, "david.bolter@gmail.com" <david.bolter@gmail.com>, "faulkner.steve@gmail.com" <faulkner.steve@gmail.com>, "franko@microsoft.com" <franko@microsoft.com>, Oliver Hunt <oliver@apple.com>, "public-canvas-api@w3.org" <public-canvas-api@w3.org>, "public-canvas-api-request@w3.org" <public-canvas-api-request@w3.org>, "public-html@w3.org" <public-html@w3.org>, "public-html-a11y@w3.org" <public-html-a11y@w3.org>, "public-html-request@w3.org" <public-html-request@w3.org>
With VoiceOver, I have to use a bunch of ugly hacks. That happens in 
compatibility work.
Hopefully my attendance to the standards mailing list, and promotion of 
bug reports, will
reduce the need to use such hacks in the future.

On the thread-- sharing path data in the context of a11y.

Once we start keeping paths around, we're going to encounter push-back 
to the next version of canvas.
The existing canvas spec allows-for the recording of all paths, but no 
implementers are doing it.

I'm still struggling for a solution which implementers might approach in 
this version.
I'm trying to round up some ideas from other canvas-users.

These are the ones I have:

Using CSS pointer-events would be an appropriate way to -enable- slower 
code paths.

pointer-events: stroke would work fine with strokeText and stroke(),
and when enabled, may stash pixels in a 1-bit bitmap, and/or a character 
buffer.

When pointer-events are set the implementation would expose the current path
to the dom or canvas2d api.

These are steps towards a long-term solution.

They both help canvas authors, pointer-events really help with DOM
management and speed-up hit testing [by memory trade-off],
and grabbing a DOMString of the path makes debugging easier.

It's reasonable to expect an AT to calculate the extents of a DOMString,
normalized SVG Path.

Those two items provide a foundation for a a few simple methods
to notify the AT that pointer/coordinate focus should be associated with 
fallback content.

I'd like to see if they have any support.

-Charles


On 3/30/2011 1:54 PM, Richard Schwerdtfeger wrote:
>
> Charles, right now the fallback content in canvas is a black hole in 
> webkit and thus Safari. So, VoiceOver can't read anything in canvas 
> without a Ouija board. (sorry, a little humor is due)
>
>
> Rich Schwerdtfeger
> CTO Accessibility Software Group
>
> Inactive hide details for Charles Pritchard ---03/30/2011 02:24:58 
> PM---Oliver, What's your take on the VoiceOver integration wCharles 
> Pritchard ---03/30/2011 02:24:58 PM---Oliver, What's your take on the 
> VoiceOver integration with canvas?
>
> From: Charles Pritchard <chuck@jumis.com>
> To: Oliver Hunt <oliver@apple.com>
> Cc: Richard Schwerdtfeger/Austin/IBM@IBMUS, Boris Zbarsky 
> <bzbarsky@mit.edu>, "cyns@exchange.microsoft.com" 
> <cyns@exchange.microsoft.com>, "david.bolter@gmail.com" 
> <david.bolter@gmail.com>, "faulkner.steve@gmail.com" 
> <faulkner.steve@gmail.com>, "franko@microsoft.com" 
> <franko@microsoft.com>, "public-canvas-api@w3.org" 
> <public-canvas-api@w3.org>, "public-canvas-api-request@w3.org" 
> <public-canvas-api-request@w3.org>, "public-html@w3.org" 
> <public-html@w3.org>, "public-html-a11y@w3.org" 
> <public-html-a11y@w3.org>, "public-html-request@w3.org" 
> <public-html-request@w3.org>
> Date: 03/30/2011 02:24 PM
> Subject: Re: feedback requested: Canvas change for improved hit 
> testing that also facilitates accessibility
>
> ------------------------------------------------------------------------
>
>
>
> Oliver,
>
> What's your take on the VoiceOver integration with canvas?
> First and foremost, we're looking to enable authors to provide more 
> information to accessibility software.
>
> This is a brainstorming thread.
>
> Ideas welcome.
>
> On Mar 30, 2011, at 12:20 PM, Oliver Hunt <_oliver@apple.com_ 
> <mailto:oliver@apple.com>> wrote:
>
>
>       On Mar 30, 2011, at 12:06 PM, Richard Schwerdtfeger wrote:
>
>             Oliver,
>
>             It is an attempt to simplify hit testing in canvas while
>             at the same time providing a vehicle to tell an assistive
>             technology the bounds of the corresponding UI object being
>             drawn on canvas as represented in fallback content.
>             Currently there is no mapping. These bounds are needed by
>             screen magnifiers for zooming and screen readers for
>             Braille support (earlier post).
>
>             Now the canvas author has to manage all the hit testing.
>             This is a canvas deficiency that should have been in place
>             to start - so grafting seems like an inappropriate
>             response. Consequently, I am also seeing canvas
>             applications that create the equivalent of visio by
>             creating separate canvas elements overlayed on top of
>             another canvas to represent drawing objects. This is very
>             inefficient and will get worse unless something is done. 
>       This is not a canvas deficiency -- canvas is an immediate mode
>       renderer, one of the things you have to handle yourself when
>       dealing with _any_ immediate mode renderer is hit detection.
>       This is true of Canvas, GDI, CG, raw component painting in Java,
>       etc, etc
>
>       If you want hit detection to be done for you, you want a
>       retained mode renderer, such as SVG.
>
>       --Oliver
>
>
>
>             Rich Schwerdtfeger
>             CTO Accessibility Software Group
>
>             <graycol.gif>Oliver Hunt ---03/30/2011 12:11:53 PM---This
>             feels like an attempt to graft retained mode rendering on
>             to canvas, what am i missing? --Olive
>
>             From: Oliver Hunt <_oliver@apple.com_
>             <mailto:oliver@apple.com>>
>             To: Richard Schwerdtfeger/Austin/IBM@IBMUS
>             Cc: Boris Zbarsky <_bzbarsky@mit.edu_
>             <mailto:bzbarsky@mit.edu>>, _chuck@jumis.com_
>             <mailto:chuck@jumis.com>, _cyns@exchange.microsoft.com_
>             <mailto:cyns@exchange.microsoft.com>,
>             _david.bolter@gmail.com_ <mailto:david.bolter@gmail.com>,
>             _faulkner.steve@gmail.com_
>             <mailto:faulkner.steve@gmail.com>, _franko@microsoft.com_
>             <mailto:franko@microsoft.com>, _public-canvas-api@w3.org_
>             <mailto:public-canvas-api@w3.org>, _public-html@w3.org_
>             <mailto:public-html@w3.org>, _public-html-a11y@w3.org_
>             <mailto:public-html-a11y@w3.org>,
>             _public-html-request@w3.org_
>             <mailto:public-html-request@w3.org>
>             Date: 03/30/2011 12:11 PM
>             Subject: Re: feedback requested: Canvas change for
>             improved hit testing that also facilitates accessibility
>             Sent by: _public-canvas-api-request@w3.org_
>             <mailto:public-canvas-api-request@w3.org>
>             ------------------------------------------------------------------------
>
>
>
>             This feels like an attempt to graft retained mode
>             rendering on to canvas, what am i missing?
>
>             --Oliver
>
>             On Mar 30, 2011, at 8:39 AM, Richard Schwerdtfeger wrote:
>
>                   Thanks Boris. Sorry for being a pest but I really
>                   want developers to work through the issues.
>
>                   So, you would do the following:
>
>                   - Assign the a closed draw path to an element in
>                   fallback content: setClickableRegion(element). This
>                   immediately makes the association and places it at
>                   the bottom of the list.
>                   - Any time you draw the element it moves it to the
>                   top of the list.
>                   - If the fallback element is removed the association
>                   would need to go away. I did not address that so I
>                   will need to add that to the proposal
>                   - When a pointer event (click, etc.) goes to the
>                   fallback element the normal capture/bubbling event
>                   processing would apply
>
>                   Rich
>
>
>                   Rich Schwerdtfeger
>                   CTO Accessibility Software Group
>
>                   <graycol.gif>Boris Zbarsky ---03/30/2011 10:05:48
>                   AM---On 3/30/11 10:55 AM, Richard Schwerdtfeger
>                   wrote: > Seeing as nobody has commented can we
>                   assume tha
>
>                   From: Boris Zbarsky <_bzbarsky@mit.edu_
>                   <mailto:bzbarsky@mit.edu>>
>                   To: Richard Schwerdtfeger/Austin/IBM@IBMUS
>                   Cc: _public-canvas-api@w3.org_
>                   <mailto:public-canvas-api@w3.org>,
>                   _public-html@w3.org_ <mailto:public-html@w3.org>,
>                   _public-html-a11y@w3.org_
>                   <mailto:public-html-a11y@w3.org>,
>                   _public-html-request@w3.org_
>                   <mailto:public-html-request@w3.org>,
>                   _chuck@jumis.com_ <mailto:chuck@jumis.com>,
>                   _cyns@exchange.microsoft.com_
>                   <mailto:cyns@exchange.microsoft.com>,
>                   _david.bolter@gmail.com_
>                   <mailto:david.bolter@gmail.com>,
>                   _faulkner.steve@gmail.com_
>                   <mailto:faulkner.steve@gmail.com>,
>                   _franko@microsoft.com_ <mailto:franko@microsoft.com>
>                   Date: 03/30/2011 10:05 AM
>                   Subject: Re: feedback requested: Canvas change for
>                   improved hit testing that also facilitates accessibility
>
>                   ------------------------------------------------------------------------
>
>
>
>                   On 3/30/11 10:55 AM, Richard Schwerdtfeger wrote:
>                   > Seeing as nobody has commented can we assume that
>                   developers have no
>                   > problem with our totally changing the canvas 2D
>                   API to support clickable
>                   > regions?
>
>                   It might just mean that people don't read their
>                   mailing list spam every
>                   few hours.
>
>                   >From reading over your proposal, I'm not sure I
>                   follow how it would
>                   behave in the face of DOM mutations (e.g. elements
>                   being removed from
>                   the fallback content).
>
>                   Or put another way, once you draw, you're
>                   permanently attaching some
>                   element to the canvas, right? Or is that not the
>                   proposal?
>
>                   -Boris 
>
Received on Friday, 1 April 2011 21:59:50 UTC

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