tree 959e2c05d82b5e5aa6983dfe45a4ffdaa80aff18
parent 993ab1ed92b9066fb6d7964948a9ced827b22f36
author Morten Stenshorne <mstensho@chromium.org> 1606821411 -0800
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1606822501 -0800

Stretch column block-size to avoid unappealing breaks.

We do not even attempt to honor orphans or widows requests during the
initial column balancing pass (since we have no idea which column is
going to get which content). Detect unappealing break points during
layout instead, and stretch the columns if possible when this happens.
This is different from the legacy fragmentation engine, which does this
during the initial column balancing pass, but this approach doesn't work
so well, since we'll have no idea which lines end up in the same
fragmentainer, and the lines may have different heights; see
crbug.com/1013151

Also stretch if possible if we violate any
break-{after,before,inside}:avoid rules. Note that it was already
working for break-inside:avoid, but not for break-after or break-before.

css/css-multicol/balance-orphans-widows-000.html also passes without
this fix, but it fails in the legacy engine, due to column
over-stretching described in crbug.com/1013151

css/css-multicol/balance-break-avoidance-000.html also passes without
this fix, but I couldn't find any test like this (break-inside:avoid and
how it affects column balancing), so here it is.

Bug: 1013151, 1066380, 829028
Change-Id: Ic4fca68644864b8209d49fa5f0d62d6079e6c0e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566810
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832279}