1390145 - Content jumps around when hiding/showing urlbar

Status: RESOLVED FIXED

(Firefox for Android Graveyard :: Toolbar, defect, P3)

Description

[James Willcox (:snorp) ([e-mail]) (he/him)]

Recently I've noticed that I get one frame where the content jumps down about $URLBAR_HEIGHT pixels. I usually notice this when the urlbar is in the process of showing or hiding.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

Nightly only, or beta too?

Comment 2

[James Willcox (:snorp) ([e-mail]) (he/him)]

Only Nightly. Easy to repro:

1) Scroll down the page slowly, enough that the urlbar starts to scroll away
2) release while the urlbar is partially hidden
3) observe about one frame of jumpy content

Comment 4

[Randall Barker [:rbarker]]

Attachment: Bug 1390145 - Disable apz.frame_delay.enabled on Fennec nightly to prevent page jitter when dynamic toolbar is animated

Review commit: https://reviewboard.mozilla.org/r/168354/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/168354/

Comment 5

[Botond Ballo [:botond]]

Comment on attachment 8897070 [details]
Bug 1390145 - Disable apz.frame_delay.enabled on Fennec nightly to prevent page jitter when dynamic toolbar is animated

https://reviewboard.mozilla.org/r/168354/#review173620

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/eb73e2d20c19
Disable apz.frame_delay.enabled on Fennec nightly to prevent page jitter when dynamic toolbar is animated r=botond

Comment 7

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/eb73e2d20c19

Comment 8

[Randall Barker [:rbarker]]

The current dynamic toolbar implementation relies on the ability to scroll the content in the same frame that the composition height is changed in the compositor thread by calling parent->GetAPZCTreeManager()->AdjustScrollForSurfaceShift() in
https://dxr.mozilla.org/mozilla-central/rev/f9a5e9ed62103c84e4cde915f4d08f1ce71be83e/gfx/layers/apz/src/AndroidDynamicToolbarAnimator.cpp#334

So that when the composition size is changed the content may be shifted to give the appearance that nothing has moved.

In particular, when the page is scrolled to the end and the toolbar is hidden, it gets animated into view. Once visible the composition bounds are reduced by the height of the toolbar. This change in composition bounds normally cause the bottom of the page to slide off the screen. To prevent this, the content is scrolled up so that the bottom of the page is still at the bottom of the page. By adding a frame delay to the scroll operation, there is a frame where the content shifts off the page and then jumps back up once the scroll is processed.