W3C home > Mailing lists > Public > public-html@w3.org > March 2011

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

From: Ian Hickson <ian@hixie.ch>
Date: Wed, 30 Mar 2011 23:49:05 +0000 (UTC)
To: Richard Schwerdtfeger <schwer@us.ibm.com>
cc: public-html@w3.org
Message-ID: <Pine.LNX.4.64.1103302342300.25791@ps20323.dreamhostps.com>
On Wed, 30 Mar 2011, Richard Schwerdtfeger wrote:
>
> Here are your real use cases: [...]

To clarify, what I meant was I think it would be good to get actual HTML 
pages that show the kinds of issues we're trying to solve. Only by having 
real content can we determine how well an API works. We can't design an 
API in a vacuum.


> - The hit testing and mouse events that are normally directed only to 
> canvas can be directed to the fallback DOM element that receives the 
> keyboard element

I don't really know what that would mean. This is the kind of thing for 
which actual HTML pages showing what you mean would be fantastic.


> - The HTML spec defines 1:1 mapping for the fallback content to the UI 
> object. This allows us to tie the bounding rectangle needed for hit 
> testing to the object.

My concern is that most of the time this won't make sense. The use of 
canvas is something that will typically happen when traditional UI 
paradigms don't work, or are not being used. There might not _be_ a 
bounding box, because the "widget", insofar as there is one, might be 
shattered into many pixels distributed across the canvas, with the pixels 
continually drifting around and just coming together when the user somehow 
indicates a desire to interact with a particular aspect of the UI.

When canvas is being used in a way that it can just be mapped straight to 
actual UI widgets it almost certainly is being misused -- if a 1:1 mapping 
is possible, then canvas is probably not necessary and one should just use 
HTML instead. (This is similar to the argument that trying to address text 
editing accessibility in canvas is misguided, since text editing should 
never be done using canvas in the first place.)

What we need are small HTML pages that show examples of UIs for which 
canvas is appropriate and for which we need accessibility hooks that are 
not yet available. It doesn't make sense to talk about this in the 
abstract without examples to look at.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Wednesday, 30 March 2011 23:49:32 GMT

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