1637091 - Skip final reflow for flex items in paginated context if it's block-size and overflow area can fit the available block-size

Status: RESOLVED FIXED

(Core :: Layout: Flexbox, enhancement)

Description

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

File per dholbert's review comment.

My WIP patch Part 3 of bug 1622935 is planning to always perform a "final reflow" for flex items in paginated context. We can improve the performance by skipping the final reflow for the flex item if the item's block-size and overflow area can fit the remaining available block-size, i.e the item doesn't need to be pushed or split, and can be moved to its final position.

Comment 1

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

Attachment: Bug 1637091 - Always reflow a flex item in a fragmented context.

nsColumnSetFrame can reflow its last column in an unconstrained available
block-size to measure the total block-size of the content [1]. This patch adds a
helper method in ReflowInput for that.

For flex items in a fragmented context, we cannot skip its final reflow
because fragmentation might grow its block-size if there's any force break in
it (bug 1663079), or if it has repeated table header/footer (bug 1744363).

This patch doesn't change observable behavior. It potentially does extra final
reflow for flex items in last column with an unconstrained available block-size,
but this is the right thing to do.

[1] https://searchfox.org/mozilla-central/rev/daf613efc5c358f3a94961d73b90472c00703838/layout/generic/nsColumnSetFrame.cpp#614-621

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/34f2732d6954
Always reflow a flex item in a fragmented context. r=dholbert

Comment 3

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/34f2732d6954