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[Bug 12306] "When authors use the canvas element, they must also provide content that, when presented to the user, conveys essentially the same function or purpose as the bitmap canvas." While everyone can probably agree that alternative content is a good idea when f

From: <bugzilla@jessica.w3.org>
Date: Tue, 17 May 2011 21:51:35 +0000
To: public-html-a11y@w3.org
Message-Id: <E1QMSAx-00018p-1l@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=12306

--- Comment #6 from Rich Schwerdtfeger <schwer@us.ibm.com> 2011-05-17 21:51:33 UTC ---
The right way to do this is to expand the Canvas 2D API spec. to handle
clickable regions to support hit testing. I mentioned this on the public-html
list. Essentially, we would define a closed path for the bounds of an object
and associate it with an element in fallback content. It would require canvas
implementations to manage the last drawn of an object to deal with overlapping
regions. 

So you would define a path and then call something like:
setClickableRegion(element);

Then canvas would be able to process a ptInPath on the mouse, for clicks,
onmouseover, and onblur and route the event to the element in fallback content
that processes the keyboard events for the drawing object. The bounds of the
object would supply the accessibility API mapping for the element. 

This also provides the author with ability to do canvas managed hit testing
that is not limited to the shapes defined by image maps and in fact the ability
to bind the the object to richer HTML objects in fallback content would make
this even more powerful.

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