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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
Summary: "When authors use the canvas element, they must also provide content that, wh...
Status: CLOSED WONTFIX
Alias: None
Product: HTML WG
Classification: Unclassified
Component: LC1 HTML5 spec (show other bugs)
Version: unspecified
Hardware: Other other
: P3 normal
Target Milestone: ---
Assignee: contributor
QA Contact: HTML WG Bugzilla archive list
URL: http://www.whatwg.org/specs/web-apps/...
Whiteboard:
Keywords: a11y, a11ytf, a11y_canvas
Depends on:
Blocks:
 
Reported: 2011-03-15 13:37 UTC by contributor
Modified: 2012-11-15 17:18 UTC (History)
20 users (show)

See Also:

Attachments

Description contributor 2011-03-15 13:37:35 UTC 
Specification: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html
Section: http://www.whatwg.org/specs/web-apps/current-work/#the-canvas-element

Comment:
"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 feasible, when considering what people are using
the canvas for, which seems to fit the examples provided in the first
paragraph well, the wording "they must" doesn't make any sense to me. How on
earth do you expect authors to provide alternative content for a game or a
complex visualization? I suggest either softening the first sentence up or
just whacking it entirely. Otherwise thanks for a nice and clear spec. :)

Posted from: 77.243.62.134
User agent: Mozilla/5.0 (X11; U; Linux i686; da-DK; rv:1.9.2.15) Gecko/20110303 Ubuntu/10.10 (maverick) Firefox/3.6.15
Comment 1 Ian 'Hixie' Hickson 2011-05-06 20:11:50 UTC 
Anyone have an opinion on this that I should know about before I resolve the bug? :-)
Comment 2 steve faulkner 2011-05-06 20:31:08 UTC 
(In reply to comment #1)
> Anyone have an opinion on this that I should know about before I resolve the
> bug? :-)

yes, I request you do not change the spec wording at this time, if you have a change in mind, send a diff to public html for review.
Comment 3 Benjamin Hawkes-Lewis 2011-05-06 21:25:55 UTC 
(In reply to comment #1)
> Anyone have an opinion on this that I should know about before I resolve the
> bug? :-)

It is not obvious that games and complex visualizations cannot be made accessible
using sub-DOM in combination with other techniques. See also:

http://lists.w3.org/Archives/Public/public-html/2011Apr/0801.html
Comment 4 Tab Atkins Jr. 2011-05-09 17:39:16 UTC 
I think the note should be softened as well.  While Benjamin's email points out many interesting methods that can be explored to expose some types of visualizations to certain kinds of non-visual users, they are still limited (most wouldn't apply to spiders) and most are both experimental and fairly complex, rendering them unsuitable for authors at this time.  Even if we had the hardware APIs necessary to implement an audio-haptic mapping of my mandelbrot set generator (we don't), I wouldn't know how to use it properly.  This is the sort of thing that still requires a ton of research and study, and likely will only be truly usable when it's driven by a sufficiently intelligent automatic system rather than implemented manually by authors.
Comment 5 Martin Kliehm 2011-05-10 15:17:22 UTC 
Adding the a11yTF keyword. The bug triage sub-team thinks we should keep an eye on this bug, the current wording of the spec shouldn't be changed.
Comment 6 Rich Schwerdtfeger 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.
Comment 7 Michael[tm] Smith 2011-08-04 05:00:25 UTC 
mass-moved component to LC1
Comment 8 Ian 'Hixie' Hickson 2011-12-02 17:52:16 UTC 
EDITOR'S RESPONSE: This is an Editor's Response to your comment. If you are satisfied with this response, please change the state of this bug to CLOSED. If you have additional information and would like the editor to reconsider, please reopen this bug. If you would like to escalate the issue to the full HTML Working Group, please add the TrackerRequest keyword to this bug, and suggest title and text for the tracker issue; or you may create a tracker issue yourself, if you are able to do so. For more details, see this document:
   http://dev.w3.org/html5/decision-policy/decision-policy.html

Status: Rejected
Change Description: no spec change
Rationale: If I make this change it'll just get a revert request. I agree the change needs to be made, but I don't care enough to go through the motions here. If anyone wants to escalate this I'd be happy to work with you to provide a patch.
Comment 9 Léonie Watson 2012-11-15 17:18:09 UTC 
Comment via Rich Schwerdtfeger:

This text exists in the canvas element specification: 
"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. This content may be placed as content of the canvas element. The contents of the canvas element, if any, are the element's fallback content."