1924792 - Implement position-area "shifting" for containing block overflow

Status: RESOLVED FIXED

(Core :: Layout, enhancement, P3)

Description

[Jonathan Watt [:jwatt]]

At the end of the position-area section there is a note about shifting when there's containing block overflow. We'll need to implement this behaviour.

Comment 1

[David Shin[:dshin]]

Also see spec resolution added to "see also," that avoids layout inconsistencies when anchor is out of vs within the initial viewport.
However, I am unsure of what WPT implications, if any, as a result of this behaviour change.

Comment 2

[Jonathan Watt [:jwatt]]

Not really part of the initial support, which has landed. Changing this to block the main meta bug.

Comment 4

[David Shin[:dshin]]

So we're position-area ends up using 0 for auto, but we're still changing alignment based on it:

However, if only one inset property in the relevant axis is auto, the default alignment is instead towards the edge with the non-auto inset; and this is an unsafe alignment.

This happened as part of this spec resolution.
Safari seems to implement this, but still agrees with Chrome on the usecase, except the manual additional inset without use of anchor functions. I believe the solution is that we should shift the offset by the position-area modified inset. e.g. With position-area: bottom right, left: anchor(right) should resolve to 0.

Comment 5

[David Shin[:dshin]]

It seems that, after bug 1991929:

• bug 2003568 will mostly be fixed, though this bug is required to reach parity with Chrome
• bug 2003519, 2003528, 2003548 actually seem better served by bug 2003591, since they all specify anchor() inset on top of position-area.

Comment 6

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1924792 - If an anchored element overflows its position-area IMCB, try to shift it to stay within the original containing block. r=#anchor-pos

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/2a64929749ca
https://hg.mozilla.org/integration/autoland/rev/cdeb248c5061
If an anchored element overflows its position-area IMCB, try to shift it to stay within the original containing block. r=layout-anchor-positioning-reviewers,layout-reviewers,emilio

Comment 8

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/cdeb248c5061

Comment 9

[Jonathan Kew [:jfkthame]]

Our rendering for the testcase in bug 2003568 now matches Chrome's; and this has fixed a couple of the WPT failures in bug 1897279.

Comment 10

[Donal Meehan [:dmeehan]]

:jfkthame, could you consider nominating this for a release note? (Process info)

Comment 11

[Jonathan Kew [:jfkthame]]

This doesn't really seem relnote-worthy to me; it's just an incremental fix/improvement to our anchor positioning support, which is a work in progress, but I don't think each fix we make in that feature gets its own individual note?

(But re-ping me if you think my understanding is off-base here.)