Re: hit testing and retained graphics

Yes. Flash has retained mode graphics.  We have it now in canvas in that we
can create a DOM node but we just can't associate it with the object being

Canvas has one big drawing object and associated context - the canvas
itself. Without the ability to tell a magnifier where the objects are on
the canvas, represented in the fallback content, we cannot direct the
magnifier to zoom on the object when it receives focus or when the AT
simply wants to zoom to the object in the accessibility  object tree
produced by the user agent from the canvas subtree.

In an earlier proposal I suggested producing a subclass of the canvas
object that had the same context APIs to represent drawing objects  to
start. ... that is if we were to produce canvas with full retained mode
graphics. Frankly, this is not unlike what developers are forced to do.
Developers are producing separate canvas elements and overlaying them on
top of canvas to produce drawing objects that appear on top of canvas.

Rich Schwerdtfeger
CTO Accessibility Software Group

From:	Maciej Stachowiak <>
To:	Silvia Pfeiffer <>
Cc:	Richard Schwerdtfeger/Austin/IBM@IBMUS, Charles McCathieNevile
            <>, Cameron McCormack <>, Charles
            Pritchard <>, Cynthia Shelly
            <>,, Frank Olivier
            <>, "Tab Atkins Jr."
Date:	06/28/2011 12:26 PM
Subject:	Re: hit testing and retained graphics
Sent by:

On Jun 28, 2011, at 7:35 AM, Silvia Pfeiffer wrote:

      On Mon, Jun 27, 2011 at 10:41 PM, Richard Schwerdtfeger
      <> wrote:

      What about Adobe Flash in this area? Adobe Flash is used for many of
      the same use cases that canvas is used for. Is Flash more accessible?
      How do they do it? Is Flash prohibited because it's not accessible?

I'm not an expert on Adobe Flash accessibility, but my understanding is
that its drawing model is more like SVG (retained mode) than like Canvas
(immediate mode). Thus, there are persistent objects that represent your


Received on Tuesday, 28 June 2011 17:51:24 UTC