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Re: [whatwg] Media query for bandwidth ??

From: Florian Rivoal <florian@rivoal.net>
Date: Sat, 10 Dec 2016 11:14:21 +0900
Message-Id: <B042C0C5-868D-4DFA-92AA-A428910A6A3F@rivoal.net>
To: "Michael A. Peters" <mpeters@domblogger.net>
Cc: whatwg@lists.whatwg.org
> On Dec 9, 2016, at 23:07, Michael A. Peters <mpeters@domblogger.net> wrote:
> This was inspired by inspection of a style-sheet in the wild that uses screen-width to try and reduce bandwidth needs of mobile devices.
> I like the concept, but very often I use my mobile devices where bandwidth doesn't matter and my laptop via a mifi where bandwidth does matter.
> I would like a CSS media query for bandwidth so that I can reduce how many webfonts are used in low bandwidth scenarios. It seems browsers are already smart enough to only download a font defined by @font-face if they need it, so it only needs to be done where the font is used, e.g.

It's been considered before, and that approach will not work. Media queries are the wrong tool for this. Neutrality / bias warning: I'm co-editor of the Media Queries spec.

Media queries, by design, will switch instantly when the environment changes, stop applying the old styles, and start applying the new ones. So if you finish loading a page on your phone in your home wifi with the high-res and heavy assets, start reading, then walk outside into 3G, you'll discard the high res assets and start loading the low res ones. And if you're driving / riding a train in and out of tunnels, you'll toggle between high and low (or low and terrible) constantly, and never manage to finish loading anything, all while using copious amounts of bandwidth. This isn't a bug, this is how Media Queries work, and is the right thing to do for things where media queries are the right tool. If that's not what you want, what you want isn't a media query.

The right approach is something like srcset[1], the source element[2], or image-set()[3]: instead of switching between one variant or another based on a hard criteria, you provide the UA with all the variants you have, and let it switch intelligently.

Of course, these are UA based heurisitics, it is certainly possible that the UA will make poor decisions sometimes, but that's a lot better than the guaranteed bad behavior you'd get with Media queries.

For fonts, there isn't currently an equivalent mechanism, but we could think of adding qualifiers either the @font-face that declares the font, or font-family that tries to use it, to indicate that certain fonts are must-have, while others are optional things that are fine to skip in case of bad bandwidth or latency.

There's already one proposal in that direction, although it hasn't received much attention lately: https://tabatkins.github.io/specs/css-font-display/ 

Finally, while you're free to talk about this anywhere you like, traditionally the best forum for CSS related topics is the CSSWG, either through its github[4] or its mailing list[5].


[1] https://html.spec.whatwg.org/multipage/embedded-content.html#attr-img-srcset
[2] https://html.spec.whatwg.org/multipage/embedded-content.html#the-source-element
[3] https://drafts.csswg.org/css-images-3/#image-set-notation
[4] https://github.com/w3c/csswg-drafts/issues
[5] https://lists.w3.org/Archives/Public/www-style/
Received on Saturday, 10 December 2016 02:14:57 UTC

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