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Re: Is algorithm for selecting based on media query defined?

From: Aaron Gustafson <aaron@easy-designs.net>
Date: Thu, 17 May 2012 09:03:25 -0700
To: Scott Jehl <scott@scottjehl.com>
Cc: Kornel Lesiński <kornel@geekhood.net>, public-respimg@w3.org, Matthew Wilcox <mail@matthewwilcox.com>
Message-ID: <61B77086BC7347709829B057DBD35786@easy-designs.net>
On Thursday, May 17, 2012 at 8:55 AM, Scott Jehl wrote:
> Fwiw, when working on the picturefill prototype/polyfill, we decided that the last source element that matched would be used.  
> And they would be reassessed on resize, orientation change, etc.
>  
> I guess since it's a media query feature, it seemed like mimicking CSS cascade/overriding felt natural there.
>  

While I can definitely understand and respect your choice, it does seem to go against existing standards (assuming I am reading the source selection spec correctly). I think if we are going to pursue picture (and I believe we should), and we are using audio/video as a basis for the element, we need to be as true to the existing standards as possible. Make sense?

Cheers,

Aaron

--  
Aaron Gustafson
@AaronGustafson
aaron-gustafson.com

-------
Aaron takes no responsibility for poor spelling in this message. It was pecked out by fat fingers on a tiny screen.


  
>  
>  
> On May 17, 2012, at 8:46 PM, Aaron Gustafson wrote:
>  
> > On Thu, May 17, 2012 at 7:47 AM, Kornel Lesiński <kornel@geekhood.net> wrote:
> > > On Thu, 17 May 2012 15:22:04 +0100, Aaron Gustafson <aaron@easy-designs.net>
> > > wrote:
> > >  
> > > > Traditionally, the first to match is the one picked. In the video
> > > > element, this is why we put WebM before Ogg: the same browsers support
> > > > both, but WebM is smaller, so we put it first so it is the one that’s
> > > > downloaded.
> > > >  
> > >  
> > >  
> > >  
> > > Is that the case for <picture> as well? It doesn't seem to match examples.
> > >  
> > > How is interpreted source without media? (media="all"? media="none"?)
> > >  
> > >  
> > > http://www.w3.org/community/respimg/2012/03/07/14/
> > >  
> > > <picture alt="Alt tag should accurately describe the image represented by
> > > all sources, though cropping and zooming may differ.">
> > > <source src="mobile.jpg" /> <!-- Matches by default. -->
> > > <source src="high-res.jpg" media="min-width: 800px" /> <!-- Overrides the
> > > previous source over 800px before any assets are fetched, resulting in a
> > > single request. -->
> > > <img src="mobile.jpg" /> <!-- Fallback content, in the event the <picture>
> > > tag is completely unsupported by the user’s browser. -->
> > > </picture>
> > >  
> > > In that case I'd expect <source src="mobile.jpg"> to always match and
> > > <source src="high-res.jpg"> be impossible to use.
> > >  
> >  
> >  
> >  
> > You are correct that it doesn’t match up with the examples. This is
> > one thing that will have to worked through from an implementor’s
> > perspective. We need hard and fast rules for precedence. The model
> > picture is now using seems more like the cascade of style sheets than
> > the way video and audio sources are handled.
> >  
> > In terms of the source element, media queries are evaluated after the
> > media type in the process (see "resource selection algorithm":
> > http://dev.w3.org/html5/spec/single-page.html#concept-media-load-algorithm
> > step 6’s else flow #6) and failure to apply a given source (based on
> > media query or otherwise) results in a move to the next source.
> > Picture would need to function the same way lest we cause confusion
> > for either element type.
> >  
> > Cheers,
> >  
> > Aaron
> >  
> > ----
> > Aaron Gustafson
> > Principal
> > Easy Designs, LLC
> > +1 877 EASY 313 x101
> > aaron@easy-designs.net
> > @aarongustafson
> >  
> > === OUT NOW ===
> > Adaptive Web Design: Crafting Rich Experiences with Progressive Enhancement
> > http://adaptivewebdesign.info
> >  
>  
>  
>  
Received on Thursday, 17 May 2012 16:04:08 GMT

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