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Re: [css-flexbox] Intrinsic sizes and flexibility

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 12 Jan 2015 11:09:56 -0800
Message-ID: <CAAWBYDD665hM1pP1m0juV7TgA4hcEW-06CU7t+VS-pF7h0bM_w@mail.gmail.com>
To: Lev Solntsev <greli@mail.ru>
Cc: www-style <www-style@w3.org>
On Sun, Jan 11, 2015 at 7:50 AM, Lev Solntsev <greli@mail.ru> wrote:
> Hello!
> There is interesting case questioned at http://toster.ru/q/170371 (in
> russian).
> In short, it was asked to make an image with a caption beneath centered
> using Flexbox. When the page is too narrow or short the image should
> be smaller. I've made an example here:
> http://codepen.io/GreLI/pen/RNKoxo
> One can see that the image there doesn't keep its proportions. It become
> smaller proportionally when page is too narrow with ‘max-width: 100%’,
> but it doesn't in case of height.
> When ‘max-height: 100%’ is set, image height resolves relative to the
> whole ‘display: flex’ element (i.e. <figure>) height, including the
> caption height. The worst part is that one can't limit the height
> using wrapping element since it wouldn't have definite height.
> (And in case of setting height it would resolve against the value that
> was set, not the flexible one.)
> I guess it happens because there is no place in spec that says that
> replaced elements should keep it intrinsic proportions after resolving
> flexible lengths.
> I believe it's a considerable defect which breaks author expectations.

Flexbox actually honors intrinsic proportions in two different spots
in its algorithm.  The issue is that there are multiple ways to honor
intrinsic proportions, when combined with explicitly-specified
proportions, and you can't handle all of them with any single set of
rules (because the behaviors are contradictory sometimes).

In this case, your use of max-height accidentally invokes the stronger
"I really want it to stay this ratio, dammit" algorithm in CSS 2.1,
defined at <http://dev.w3.org/csswg/css2/visudet.html#min-max-widths>
(in the table near the bottom of the section).  But, as you note, a
percentage max-height is calculated relative to the container, so it
only kicks in when the intrinsic size of the element is less than the
entire flexbox height, which means the image will squish somewhat
before the aspect-ratio-maintaining algo kicks in.

Unfortunately, there's no way to opt into the stronger
aspect-ratio-maintaining behavior without min/max width/height, and
there's no way to get the behavior you want with min/max width/height.
This will be handled in the future with an aspect-ratio property that
can opt elements with intrinsic dimensions into the weaker or stronger
algorithm explicitly, avoiding the need for these kinds of hacks.
Unfortunately, that's not going to help you right now.

Sorry. :(

Received on Monday, 12 January 2015 19:10:44 UTC

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