1484884 - Incorrect async adjustment of fixed elements when zooming

Status: RESOLVED FIXED

(Core :: Panning and Zooming, defect, P3)

Description

[u608768]

Attachment: position-fixed-async-zoom.html

When async-zooming, the adjustment applied to fixed elements is incorrect.

This is a result of bug 1465616, which was responsible for changing the viewport that fixed elements are attached to (both when reflowing and when compositing). This doesn't appear to be a problem when fixed elements are attached to the visual viewport (i.e., when the visual viewport is larger than the layout viewport), but I could be wrong.

Comment 1

[Botond Ballo [:botond]]

Note that there are already tests for this in the tree (currently marked as expected-fail): they were added in the "Add failing fixed-position async-zoom reftests" patch in bug 1465616.

Comment 3

[Botond Ballo [:botond]]

Kashav, I assume you're not working on this :)

Comment 4

[Botond Ballo [:botond]]

Coordinate system issues are good problems to think through during a flight :)

The issue here is that, unlike the visual viewport, the layout viewport does not change size (in terms of CSS coordinates) when zooming. Therefore, if we're trying to keep something fixed to the layout viewport, we don't want to be compensating for the zoom transform applies to the enclosing container layer.

Comment 5

[Botond Ballo [:botond]]

Attachment: Bug 1484884 - Fix async zoom transform computation for layout viewport. r=kats

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/276287cba1de
Fix async zoom transform computation for layout viewport. r=kats

Comment 7

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/276287cba1de

Comment 8

[Botond Ballo [:botond]]

Comment on attachment 9030113 [details]
Bug 1484884 - Fix async zoom transform computation for layout viewport. r=kats

[Beta/Release Uplift Approval Request]

Feature/Bug causing the regression: Bug 1465616

User impact if declined: When pinch-zooming on mobile, position:fixed elements are incorrectly positioned during the zoom. At the completion of the zoom, they jump to their correct positions.

Is this code covered by automated tests?: Yes

Has the fix been verified in Nightly?: Yes

Needs manual test from QE?: No

If yes, steps to reproduce: 

List of other uplifts needed: None

Risk to taking this patch: Low

Why is the change risky/not risky? (and alternatives if risky): Targeted change that affects only the positioning of fixed elements during async zooming.

String changes made/needed:

Comment 9

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9030113 [details]
Bug 1484884 - Fix async zoom transform computation for layout viewport. r=kats

[Triage Comment]
Fixes odd positioning of position:fixed elements during pinch zooming. Approved for 64.0b5.

Comment 10

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-beta/rev/663b56166037