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Re: CfC: Approve overview of Canvas testing in view of permissive CR exit criteria

From: Mark Sadecki <mark@w3.org>
Date: Wed, 04 Sep 2013 23:21:24 -0400
Message-ID: <5227F8B4.8060003@w3.org>
To: public-html-admin@w3.org, HTML A11Y TF Public <public-html-a11y@w3.org>
The HTML Accessibility Task Force has reviewed the HTML Canvas 2D Context Status Report [1], developed independent tests and evaluated the tests referenced in the status report [2].

The TF was concerned with the fact that browsers had not yet implemented system and custom focus rings or hit regions and that there was a possibility they would be dropped from the spec (accessibility in Canvas is not possible without these features). We have been following recent developments, occurring over the past few weeks, in basic support for system and custom focus rings in Chrome and Safari and progress towards a solution in Mozilla browsers.  Early testing shows promise.  However, extensive testing of these evolving solutions will be required to fully understand how keyboards and access technology will interact with and access these new features. There is a convincing demo [3] of focus ring implementation in Chrome Canary with experimental Canvas features enabled.  The fate of hit regions in this version of the spec is less promising and we believe accessibility of Canvas in HTML5 will be reduced without support for this feature.

In reviewing the tests for fallback content [4] we did not find any that tested focusable or interactive content as fallback for the canvas element.  We conducted independent tests and found that there was solid support for focusable elements like anchors. However, there was poor support for form elements or other interactive content when they were included as children of the canvas element.

While evaluating current support for section 12 - Drawing text to the bitmap [5], specifically measureText() and its available attributes, our independent tests could not confirm support for any of the attributes beyond 'width':

- width : supported
- actualBoundingBoxLeft : unsupported
- actualBoundingBoxRight : unsupported
- fontBoundingBoxAscent : unsupported
- fontBoundingBoxDescent : unsupported
- actualBoundingBoxAscent : unsupported
- actualBoundingBoxDescent : unsupported
- emHeightAscent : unsupported
- emHeightDescent : unsupported
- hangingBaseline : unsupported
- alphabeticBaseline : unsupported
- ideographicBaseline : unsupported

Querying the value of any of the unsupported properties returns 'undefined.'

The TF believes the accessibility of Canvas can be improved by working more closely with ongoing Canvas testing efforts.

Kind regards,

Mark Sadecki
On behalf of the HTML Accessibility Task Force

[1] http://dev.w3.org/html5/misc/canvas-implementation.html
[2] http://lists.w3.org/Archives/Public/public-html-admin/2013Jul/0032.html
[3] http://www.w3.org/2013/09/accessible_canvas_clock.html
[4] http://philip.html5.org/tests/canvas/suite/tests/index.fallback.html
[5] http://htmlwg.org/canvas-cr-heartbeat/#drawing-text-to-the-bitmap

On 7/16/13 2:26 PM, Paul Cotton wrote:
> This is a Call for Consensus (CfC) to approve the following document that indicates which parts of the Canvas  specification can be considered interoperable as per the permissive CR exit criteria [1].  The items subject to this CfC are marked "Considered interoperable" and color coded in green in the document:
> http://dev.w3.org/html5/misc/canvas-implementation.html
> Silence will be taken to mean there is no objection, but positive responses are encouraged. Objections should be made to specific entries in the document.  Objections of the form "features in Section 4.a LineWidth are not currently interoperable" MUST be accompanied with specific evidence of non-interoperability, otherwise such objections will not be accepted by the Chairs.
> If there are no objections by 16 Aug 2013, this resolution will carry.
> /paulc
> HTML WG co-chair
> [1] http://dev.w3.org/html5/decision-policy/public-permissive-exit-criteria.html
> Paul Cotton, Microsoft Canada
> 17 Eleanor Drive, Ottawa, Ontario K2E 6A3
> Tel: (425) 705-9596 Fax: (425) 936-7329

Mark Sadecki
Web Accessibility Engineer
World Wide Web Consortium, Web Accessibility Initiative
Telephone: +1.617.715.4017
Email: mark@w3.org
Web: http://w3.org/People/mark
Received on Thursday, 5 September 2013 03:21:28 UTC

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