W3C home > Mailing lists > Public > www-style@w3.org > February 2013

Re: [css3-flexbox][css3-linebox] (edge case) negative outer size and line layout

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 4 Feb 2013 23:47:57 -0800
Message-ID: <CAAWBYDBgCJ=g6GZCjPknJmr5gY+upjHfAp6WndD02NtYm5MQnQ@mail.gmail.com>
To: "Kang-Hao (Kenny) Lu" <kennyluck@csail.mit.edu>
Cc: WWW Style <www-style@w3.org>
On Fri, Aug 3, 2012 at 8:08 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> On Fri, Aug 3, 2012 at 2:47 AM, Kang-Hao (Kenny) Lu
> <kennyluck@csail.mit.edu> wrote:
>> The spec has a imprecise informative note:
>>
>>   # Note that items with zero main size will never start a line unless
>>   # they're the very first items in the flex container, or they're
>>   # preceded by a forced break. The "collect as many" line will collect
>>   # them onto the end of the previous line even if the last non-zero
>>   # item exactly "filled up" the line.
>>
>> because when the last non-zero item overflows the line, the next item
>> with zero main size will start next line. This is demonstrable[1] in
>> Chrome 22.
>
> That's a good point.  The note is actually wrong.  I'll correct it.
>
>> I think it's fine to leave the paragraph as it is (it's informative
>> anyway), but it would be nice if css3-linebox specs this simple
>> algorithm* because in inline layout browser are not currently
>> interoperable in this edge situation (again, see [1], for
>> 'inline-block's with negative outer size).
>
> Yes, it would be useful to have a generic algorithm for this, so we
> don't have to redefine it every time.
>
>> A similar edge situation is for flex items with negative outer
>> cross-size. The current spec determines the cross-size of a flex line with:
>>
>>   # (single line flex container)
>>   #
>>   # Otherwise, for each flex line:
>>   #
>>   # - Collect all the flex items whose inline-axis is parallel to the
>>   #   main-axis, whose ‘align-self’ is ‘baseline’, and whose
>>   #   cross-axis margins are both non-‘auto’. Find the largest of the
>>   #   distances between each item's baseline and its hypothetical outer
>>   #   cross-start edge, and the largest of the distances between each
>>   #   item's baseline and its hypothetical outer cross-end edge, and
>>   #   sum these two values.
>>   #
>>   # - Among all the items not collected by the previous step, find the
>>   #   largest outer hypothetical cross size.
>>   #
>>   # - The used cross-size of the flex line is the larger of the numbers
>>   #   found in the previous two steps.
>>
>> The spec should mention whether and when these calculations are clamped
>> at 0. If we want to spec Chrome 22's behavior, from testcases like
>>
>>   data:text/html,<!DOCTYPE html><div style="width: 40px; border: yellow
>> 20px solid; display: flex; -webkit-flex-flow: wrap;"><span style="width:
>> 60px; background: blue; height: 20px; -webkit-flex: none;"></span><span
>> style="width: 20px; height: 20px; background: red; margin-top:
>> -40px"></span></div>
>>
>> and
>>
>>   data:text/html,<!DOCTYPE html><div style="width: 40px; border: yellow
>> 20px solid; display: -webkit-flex; -webkit-flex-flow: wrap;"><span
>> style="width: 60px; background: blue; height: 20px; -webkit-flex:
>> none;"></span><span style="width: 20px; height: 20px; background: red;
>> margin-top: -40px; -webkit-align-self: baseline;">g</span></div>
>>
>> , it seems that what would be needed is
>>
>>   | - Collect all the flex items whose inline-axis is parallel to the
>>   |   main-axis, whose ‘align-self’ is ‘baseline’, and whose
>>   |   cross-axis margins are both non-‘auto’. Find the largest of the
>>   |   distances between each item's baseline and its hypothetical outer
>>   |   cross-start edge (or zero when all hypothetical outer cross-start
>>   |   edges are below the baseline), and the largest of the distances
>>   |   between each item's baseline and its hypothetical outer cross-end
>>   |   edge (or zero when all hypothetical outer cross-end
>>   |   edges are above the baseline), and sum these two values.
>>   |
>>   | - Among all the items not collected by the previous step, find the
>>   |   largest outer hypothetical cross size, clamped at 0.
>>
>> Otherwise, I don't particularly think negative cross-size for flex lines
>> are terrible. We don't have line boxes with negative cross-size because
>> there are struts for 'line-height', which stands for "minimum
>> cross-size", but we don't have such a thing for flex lines so I don't
>> think the consistency is in favor of any side.
>>
>> I suggest we do whatever would result in less code in browsers.
>
> Ah, I didn't consider that boxes can have a negative outer size.
> Silly me.  Yes, clamping at zero is the most sensical behavior here.

Woo, long overdue fixes! Fixed the note and made flex lines clamp
their cross size at 0.

~TJ
Received on Tuesday, 5 February 2013 07:48:44 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:21:05 GMT