commit e921f8b336061ae8e6d2af3995f2fc4e691ad9f0
author Alison Maher <almaher@microsoft.com> Wed Apr 28 21:59:50 2021
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> Wed Apr 28 22:23:08 2021
tree add495f718c7c75fbd433997fd2cdedcd2401540
parent dacc75fcce6a1a828d65ceb66ce2124312f19f84

[LayoutNG] Relative offset for fragmented OOF elements

There were a couple of issues with how relative positioning was being
applied for OOF elements during fragmentation:

1. The relative inline inset was not being applied to the OOF
descendants.
2. The relative block inset was being applied, but it was being applied
before fragmentation, which is not correct.

The reason that the relative inline inset was not being applied was
that we were only ever propagating the block offset of the containing
block as OOF fragmentainer descendants were being propagated up the
tree inside NGContainerFragmentBuilder::PropagateOOFPositionedInfo().
This was incorrect - both the inline and block offset of the containing
block should be accumulated as the OOFs propagate up the tree.

Because ancestor inline offsets are now applied as the OOF makes its way
up the tree, a new issue was identified regarding CL:2836226. In
CL:2836226, the fragmentainer offset was applied to the OOF offset
in NGOutOfFlowLayoutPart before PropagateOOFPositionedInfo() was called.
However, we only want to apply the fragmentainer offset for descendants
whose containing block is outside the fragmentation context of the
ancestor OOF element. To fix this, the fragmentainer offset is
passed into PropagateOOFPositionedInfo() as a separate variable
(offset_adjustment) to ensure that this offset is only applied in
the correct scenarios.

The relative block inset was being applied before fragmentation because
the relative ancestor's offset included its insets by the time the OOF
element was laid out. To fix this, pass the relative ancestor's
un-adjusted offset and relative offset into NGContainerFragmentBuilder::
PropagateChildData()/PropagateOOFPositionedInfo() to ensure that we
don't apply the relative offset too early in this case.

To ensure the relative offset is applied after fragmentation of an
OOF descendant, an additional variable was added to the
NGContainingBlock struct stored in NGOutOfFlowPositionedNode for the
accumulated relative_offset of the containing block. This is then
applied after the OOF descendant is laid out and fragmented.

Note: This CL does not handle the case of an inline containing block
with relative insets. This will be investigated as a follow-up
given that inline CBs have not been addressed in general for fragmented
OOF elements.

Bug: 1142387,1158756,1158387
Change-Id: I1ac3920234497459e68d5418b992791f8b50badb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2851595
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Alison Maher <almaher@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#877243}