[html4all] CANVAS (was Discussion: "Accept requirement...
chaals at opera.com
Sat Nov 24 08:29:25 PST 2007
On Wed, 21 Nov 2007 20:31:03 +0100, John Foliot <foliot at wats.ca> wrote:
> Charles McCathieNevile wrote:
>>> However, the real question is "Does <canvas> allow
>>> for fallback content at all?", and the draft spec.
>>> totally fails to clarify this.
>> As far as I can see it does so. Otherwise I would be raising hell -
>> as an implementor of canvas, we need this. In any case, it should
>> never be allowed forward without doing so.
> Well, the Draft Spec states:
> "When authors use the canvas element, they should 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."
(Which means it works like the object element...)
> ...I would surmise that "...content that... conveys essentially the
> same function or purpose..." means a textual alternative...
Not at all.
> So question one to the draft editors then is, "*How* does the content
> author specify this other (alternative) content?"
Normally, put it inside the canvas (in minimal HTML-legal but non XHTML
syntax that I realy don't recommend to anyone ever):
<canvas id=foo width=300 height=300>
<object data=accessibleSVGVersion.svg width=300 height=300>
<p>Well, I really haven't thought hard enough. Basically, I
should put a form here, since all that really happens with
the 3D view and cool aliens and stuff is that I ask for your
name and credit card numbers and get you to select things to
(I am pretty sure that is valid HTML5 according to the current draft, and
Anne would be happy. Although I don't think I will write another example
like that for a while - I really prefer code I can paste into a normal
> As I continue to read through the Draft Spec, I note with interest many
> code examples, yet none of the current examples show an implementation
> of content that "...conveys essentially the same function or purpose as
> the bitmap canvas..."
Actually, it is not easy to do. One example would be to ask Grafio
permission to use a bunch of the code from his drawing widget  and then
provide, as fallback, one of the various SVG drawing widgets. It's a bit
artifical, but probably makes the point.
> So question two would be, "Can we have an example that specifically and
> explicitly shows authors *how* to provide this essential content?"
In principle yes. (In practice, this is complicated)
> Finally, as an addendum, I would humbly suggest that the statement
> "...they should also provide content that..." be re-written to
> state "...they MUST also provide content that...", if we are to
> ensure universal access.
This is really a seperate topic. It is clear that if you don't provide
something accessible as a fallback, then accessibility is broekn. it is
equally clear that making this a conformance requirement means that basic
conformance cannot be machine tested. I have ome thoughts on this issue,
but I will raise them seperately in the HTML-WG (following up on a thread
from DanC about 6 months ago).
> Colleagues, am I missing something here?
Only a comment about "accesskey delendum est" ;)
Charles McCathieNevile Opera Software, Standards Group
je parle français -- hablo español -- jeg lærer norsk
http://my.opera.com/chaals Try the Kestrel - Opera 9.5 alpha
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