W3C home > Mailing lists > Public > public-canvas-api@w3.org > October to December 2011

Re: Fw: Request to re-open issue 131 -USE CASES, USE CASES, USE CASES

From: Jonas Sicking <jonas@sicking.cc>
Date: Tue, 20 Dec 2011 02:22:08 -0800
Message-ID: <CA+c2ei_h0mnO4R4SbWUtiQ+Qbezgm4Qe-ijNot53GBGTDkGBpg@mail.gmail.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
Cc: chuck@jumis.com, Cynthia Shelly <cyns@microsoft.com>, david bolter <david.bolter@gmail.com>, dbolter@mozilla.com, franko@microsoft.com, Maciej Stachowiak <mjs@apple.com>, Paul Cotton <Paul.Cotton@microsoft.com>, public-canvas-api@w3.org, public-html@w3.org, public-html-a11y@w3.org, Sam Ruby <rubys@intertwingly.net>, Steve Faulkner <faulkner.steve@gmail.com>
On Mon, Dec 19, 2011 at 1:19 PM, Richard Schwerdtfeger <schwer@us.ibm.com>wrote:

>  Jonas,
> For purposes of agreement getting some consensus I would like to put the
> text discussion and focus on this use case which you had agreed we should
> support while at TPAC:
> 1. Hit Testing and the bounds of an object
> USE CASE: Regarding hit testing, it is very, very simple. In ALL operating
> systems that support an accessibility API it is ESSENTIAL that a magnifier
> be able to determine the location of an accessible object on the screen so
> that a user may zoom to it. It has absolutely nothing to do with rich text
> editing other than the fact that like all other objects we would need to
> find the text box to zoom to it. You and I, who can see, can scan a page
> and find what we want. Yet, a magnifier user may only be able to see, say a
> text box, which has focus and a few characters as the screen my be
> magnified by a factor of 10. The few characters in the text box may be all
> they see on the screen. So, to zoom to something else they will ask their
> assistive technology to do things like find an object and zoom to it - or
> they may ask it to read from the beginning of an application at the first
> accessible object and maintain a magnification point around the object
> Unlike HTML accessible canvas object reside in fallback content which is
> NOT visible. So, the screen location of these objects can NOT be found
> without programmatic intervention. In ALL accessible GUI OS platforms the
> bound so the drawing object are acquired from the device context which is
> mapped ultimately to the drawing object and then to the corresponding
> accessible object. The screen location is typically the same location used
> in hit testing.
> USE CASE: USE Braille devices also use the bounding information to assist
> in line breaks on Braille displays.
> How do I know these things? I built the offscreen model for the first GUI
> screen readers for the PC. I was hip deep in the graphics engine and
> windowing systems for both OS/2 and Windows. I also worked on one of the
> first screen magnifiers the PC - Screen Magnifier/2.
> So, there are your use cases. There is NO invention here and the text
> editor case is really a red herring as it is not the essential reason why
> we need the bounds and hit testing.
> USE CASE: The use case for hit testing is it pushes the load off the
> author to the user agent. Imagine you having to do all the GUI hit testing
> manually for your Windows app. Also, now, pointing device handling occurs
> at the canvas element while the keyboard handling is handled at an element
> in fallback content.
> Here is the accessibility API for UNIX Systems that needs the bounds (see
> BoundingBox) of an object:
> http://people.gnome.org/~billh/at-spi-idl/html/classAccessibility_1_1Component.html
> Here is the accessibility API (see accLocation) for MSAA which is used
> both Chrome and Firefox on Windows:
> http://msdn.microsoft.com/en-us/library/dd318466.aspx
> Here it the accessibility API (see Bounding Box) for an UIA provider:
> http://msdn.microsoft.com/en-us/library/ms726714(v=VS.85).aspx
> Right now, without a change to canvas we cannot supply this information to
> assistive technologies.

Yes, I definitely support the ability to associate an area of the canvas
with a element in the sub-dom (sorry, forget what the official name is, if
there is one) of the canvas element. This will enable things like
hit-testing, driving screen magnifiers, implementing
scrolling-to-part-of-canvas, etc.

I apologize if I gave the impression of otherwise.

> Do you support Frank moving forward with the setElementPath/hit test
> proposal for the working group to review and are you still supportive of
> having such an API for canvas?

I honestly have lost track of what the latest proposal is at this point.
The main goal I have is to create an API which is simple enough to use for
people to want to do their own canvas hit-testing using the API we provide.
That is how we can get the most number of people to use these APIs, and
thus create the most accessible web.

/ Jonas
Received on Tuesday, 20 December 2011 10:23:33 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 20:31:54 UTC