1699412 - Scroll position not always reflected on screen

Status: RESOLVED WORKSFORME

(Core :: Graphics, defect, P3)

Description

[Anonymous]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:86.0) Gecko/20100101 Firefox/86.0

Steps to reproduce:

Firefox for Windows: 86.0.1 (64-bit), 78.8.0esr (64-bit), 88.0a1 (2021-03-17) (64-bit)
Firefox for Linux: could not reproduce
New profile with Options/General/Use smooth scrolling = off
Navigate to a web page with vertical scroll e.g. https://bugzilla.mozilla.org/describecomponents.cgi?product=Firefox (could not reproduce on about:* pages)
Scroll the page step by step with the mouse wheel

Actual results:

Sometimes (1 in 5-10 events) a scroll event would register, but the screen would not update to reflect the current position: it would look like the page did not scroll, but an interaction other than scroll (hover over a link or call the context menu) would move the page to the new scroll position.
Note: after a failed scroll event the mouse cursor would change correctly when applicable (e.g. if the mouse was pointing at a text before scrolling, it would change to default cursor despite the screen still incorrectly showing that text at the same position).

Expected results:

Pages should update on every scroll event.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Panning and Zooming' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Comment 2

[Anonymous]

Bisected with mozregression to:
Bug 1630781 - Reorder operations to increase idempotency of sampling APZ state during a vsync interval.
Differential Revision: https://phabricator.services.mozilla.com/D72046

Comment 3

[Botond Ballo [:botond]]

(In reply to Anonymous from comment #2)

Bisected with mozregression to:
Bug 1630781 - Reorder operations to increase idempotency of sampling APZ state during a vsync interval.
Differential Revision: https://phabricator.services.mozilla.com/D72046

Thanks for tracking that down!

Assuming you were testing with WebRender enabled, could you also check whether the issue is reproducible with WebRender disabled, by setting the pref gfx.webrender.force-disabled=true in about:config?

Comment 4

[Anonymous]

(In reply to Botond Ballo [:botond] from comment #3)

Assuming you were testing with WebRender enabled, could you also check whether the issue is reproducible with WebRender disabled, by setting the pref gfx.webrender.force-disabled=true in about:config?
Yes, it's reproducible either way.

Comment 5

[Timothy Nikkel (:tnikkel)]

Could you upload your aboutsupport from an affected configuration?

Comment 6

[Anonymous]

Attachment: virtualbox vm (win7), webrender unavailable

Comment 7

[Anonymous]

Attachment: hardware, webrender enabled

Both configurations are affected.

Comment 8

[Timothy Nikkel (:tnikkel)]

I tried to reproduce with smooth scroll disabled scrolling step by step with a mouse wheel. I tried on Windows 10, 8.1, and 7. I tried every combination of webrender disabled, webrender enabled, webrender compositor disabled, software webrender. I wasn't able to reproduce.

Is there some OS setting you have changed that might be relevant? Or the mouse itself is unusual?

Comment 9

[Anonymous]

I've made a new Virtualbox VM, installed Windows 7 SP1 Pro x64, Virtualbox Guest Additions and Firefox, changed nothing except the screen resolution to match host and switched the VM to fullscreen. I tried two simple Logitech mice with same results. The issue takes some time to kick in, I scrolled through the page https://bugzilla.mozilla.org/describecomponents.cgi?product=Firefox a couple of times to catch one. It seems to get worse with continuous browser usage, with lots of tabs etc.

Comment 10

[Anonymous]

Attachment: virtualbox vm configuration

Comment 11

[Botond Ballo [:botond]]

Are you still experiencing this bug? I ask because I had a theory that perhaps this was caused by bug 1737725, which has since been fixed.

Comment 12

[Anonymous]

I'm sorry but I currently don't have access to the PC that was affected by this bug, and I couldn't reproduce it with the one I have now, not even with the old FF version in a VM.

Comment 13

[Botond Ballo [:botond]]

Thanks for checking. I'm going to close this issue for now, but please feel free to reopen if you experience it again.