[whatwg] Simplified <picture> element draft

Yoav Weiss yoav at yoav.ws
Sat Jan 4 12:16:54 PST 2014

On Sat, Jan 4, 2014 at 7:36 AM, Adam Barth <w3c at adambarth.com> wrote:

> On Tue, Dec 31, 2013 at 7:17 AM, Yoav Weiss <yoav at yoav.ws> wrote:
> > On Mon, Nov 25, 2013 at 5:33 PM, Adam Barth <w3c at adambarth.com> wrote:
> >>  Is there an editor's draft or some other relatively self-contained
> >> write-up that I could review?
> >
> > Tab has rewritten the picture spec to match the latest proposal. You
> could
> > review it at http://picture.responsiveimages.org/
> Thanks.  I'm still concerned about the issue I raised with the
> original <picture> proposal in April 2012:
> ---8<---
> In order for the HTMLPreloadScanner to issue preload requests for
> <picture> elements, the HTMLPreloadScanner would need to be able to
> evaluate arbitrary media requests.  That's difficult to do without
> joining the main thread because the media query engine works only on
> the main thread.
> --->8---
> https://groups.google.com/a/chromium.org/d/msg/blink-dev/MlE9vYVUlzg/lohBvySEIegJ
> The proposal tries to address this issue in
> http://picture.responsiveimages.org/#preloader by providing a
> whitelist of media queries that must be recognized by the preload
> scanner and giving implementations license to evaluate other media
> queries incorrectly.
> In principle, we could implement these requirements in Blink, but my
> guess is that we won't be able to implement them anytime soon.  For
> example, today we can't even parse media queries on the preload
> scanner thread.  We're likely to improve our ability to process CSS on
> background threads in order to make existing content faster.  It's
> possible in several years once we've developed fancier technology this
> design will look more feasible.

Thanks for the review. I'd like to better understand what would be required
to implement off-the-main-thread MQ evaluation in Blink. Since it's a Blink
specific discussion, I'll start a Blink-dev thread on the subject.

> In the meantime, if you're interested in seeing implementations ship
> in the near term, I would focus on designs that don't require
> evaluating media queries in the preload scanner, even if that means we
> aren't able to address all the use cases that <picture> addresses.

> Adam

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