1564726 - Content are drawn onto the bottom border of a container across columns with "box-decoration-break: clone"

Status: RESOLVED FIXED

(Core :: Layout: Block and Inline, defect, P3)

Description

[Ting-Yu Lin [:TYLin] (PST, UTC-7)]

Attachment: columns-box-decoration-break.html

See the attached columns-box-decoration-break.html. The container having box-decoration-break:clone are fragmented into two columns, and its child block shouldn't being drawn onto the container's bottom border in the first column.

I think the code that leads to this result is in [1] or somewhere in nsBlockFrame::ComputeFinalBSize().

[1] https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/layout/generic/nsBlockFrame.cpp#7411-7412

Comment 1

[Ting-Yu Lin [:TYLin] (PST, UTC-7)]

Attachment: Bug 1564726 Part 1 - Make BlockReflowInput::ComputeBlockAvailSpace return the result rect.

Comment 2

[Ting-Yu Lin [:TYLin] (PST, UTC-7)]

Attachment: Bug 1564726 Part 2 - Fix available block-size for block children in block container with box-decoration-break:clone.

If a block container has box-decoration-break:clone, its block-end border and
padding (BP) are usually drawn at the block-end edge in the current
column/page. Thus, when computing the available block-size for its children, we
should subtract its block-end border BP from it.

BlockReflowInput::ContentBSize() is the correct content-box block-size the
block container precomputed in BlockReflowInput's constructor. See
https://searchfox.org/mozilla-central/rev/c12a59323ee46b29b90c9917a3a7a70ea714ffec/layout/generic/BlockReflowInput.cpp#118-126

The remove hunk was a hack, working only for ColumnSetWrapper with
box-decoration-break:clone. It's no longer needed.

When I claim the block-end BP are usually drawn at the block-end edge, the
exception is that the block container with a definite block-size runs out of its
block-size in a column/page. In this case, the block-end BP is drawn at the
block-end edge of its content-box. The sub-tests having
box-decoration-break:clone border in box-decoration-break-bug-1249913.html
is such examples. It may seem strange that the overflowing lime boxes cannot
extend to the block-end edge of the first column, but this is expected as of
this patch because we subtract the block-end BP from the available block-size.

Depends on D138366

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/51cb3ac09506
Part 1 - Make BlockReflowInput::ComputeBlockAvailSpace return the result rect. r=emilio
https://hg.mozilla.org/integration/autoland/rev/aeaea91a4f58
Part 2 - Fix available block-size for block children in block container with box-decoration-break:clone. r=dholbert,emilio

Comment 4

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/32827 for changes under testing/web-platform/tests

Comment 5

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/51cb3ac09506
https://hg.mozilla.org/mozilla-central/rev/aeaea91a4f58

Comment 6

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot