1601868 - Using scrollbar-width:none on root element causes severe scrolling issues with WR picture caching

Status: VERIFIED FIXED

(Core :: Graphics: WebRender, defect)

Description

[MrOtherGuy]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0

Steps to reproduce:

1. Ensure WR and WR-picture-caching are enabled
2. Load any page that would overflow the viewport
3. Enter devtools style-editor and apply :root{ scrollbar-width:none }
4. Initiate scroll

Actual results:

Viewport does not scroll at all or at least not smoothly.

Expected results:

Viewport should scroll smoothly or instantly.

The issue arises whether smooth scrolling is enabled or not.

I think this problem has likely been triggered by bug 1599656 or perhaps by bug 1599965

Comment 1

[motosegaman]

I can confirm. I use a userContent.css file with the following line:

*{ scrollbar-width: none }

It hides all scrollbars. Since around Nightly turned 73, it causes severe lag when scrolling unless I disable hardware acceleration in settings.

It happens on two different machines:

1. Win10 64 bit with Pentium Gold G5400 with integrated graphics.
2. Win8 32 bit with Nvidia GT 240.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

It would be useful to run mozregression on this and see which changeset caused this. I can repro this, it is pretty visible in github for example (I was using this PR).

Comment 3

[Alice0775 White]

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=1330041fa8973ac2a56f074a7c1eee9bb1cff151&tochange=93ccc760c4dd69f63d6ac171ace357b0dd31412a

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Thank you Alice! (I couldn't get to it since I didn't have good enough internet when I wrote comment 2).

Glenn, can you take a look? Seems we're incorrectly skipping frames.

Comment 5

[Glenn Watson [:gw]]

Yup, will look into this today.

Comment 6

[Glenn Watson [:gw]]

Attachment: Bug 1601868 - Fix composition skips when scrollbars are disabled.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bdb6fc50b197
Fix composition skips when scrollbars are disabled. r=nical

Comment 8

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/bdb6fc50b197

Comment 9

[Maria Berlinger [:mberlinger], Services QA]

I've managed to reproduce this issue using Firefox 73.0a1 (2019-12-04) on Windows 10x64 by following the STR from comment 0.
This is verified fixed using Firefox 73.0b12 on the following OSes: windows 10x64 and windows 8.1x64.