1749813 - SW WR/fvwm X11: Screen glitches when scrolling with WebRender On and Smooth Scrolling Off

Status: RESOLVED WORKSFORME

(Core :: Graphics: WebRender, defect)

Description

[farblos]

Attachment: Shows lag in action

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0

Steps to reproduce:

1. Create a brand-new profile.

2. In about:preferences, switch off smooth scrolling
   (general.smoothScroll := false).

3. Navigate to a site with a rather simple web page - little to
   no CSS, JavaScript, images, etc. Some good examples:

   http://catb.org/esr/faqs/smart-questions.html
   http://www.gnus.org/manual/big-gnus.html

4. Scroll page-wise with the "Next" and "Prev"/"Prior" keys.
   Press and release the keys, do not keep them pressed. If the
   problem described in item 5. does not reproduce immediately,
   sometimes it may help to pause a bit (reading that
   smart-questions.html is always fun) and then continue
   scrolling.

Actual results:

5. Usually after a few pages, the page will not be displayed
   properly. Either some strip at the top of the page is blanked
   out or even the whole page without showing the next page. See
   attached animated gif (display-lag-ff.gif).

6. When that happens and one does not continue pressing the keys,
   the page hangs in that state indefinitely. Even, when moving
   the mouse. However, any different screen update on Firefox
   (like changing a tab button by hovering over it as shown in
   the gif) forces an update of the page.

Expected results:

5. The whole document can be scrolled through up and down with
   the keys freely without any display glitches.

The latter can be achieved by setting
gfx.webrender.force-disabled to true.

I can consistently reproduce the problem (all JSONs attached):

a) on Firefox 91.4.0esr running in an VNC/FVWM/X11 session
(display-lag-vnc-91.4.0esr.json) (Oracle Linux package)

b) on Firefox nightly running in an VNC/FVWM/X11 session
(display-lag-vnc-98.0a1.json) (direct binary download)

c) on Firefox 91.4.1esr running on Gnome/Wayland
(display-lag-wayland-91.4.1esr.json) (Debian package)

d) on Firefox 96.0 running on Gnome/Wayland
(display-lag-wayland-96.0.json) (Flatpak package from
Flathub)

but it seems to get increasingly harder to reproduce the issue
from a) to d), so if wanted to reproduce this, I'd recommend
starting with an ESR Firefox running in an VNC session.

I cannot reproduce the issue for the configurations c) and d)
when running on Gnome/X11. But then on that combination I have:
WEBRENDER_COMPOSITOR: blocklisted by env: Blocklisted by gfxInfo

Comment 1

[farblos]

Attachment: Support JSON for nightly FF on VNC

Comment 2

[farblos]

Not sure whether you need all these JSONs from the different Firefoxes, limiting this to the most recent one for now.

Comment 3

[BugBot [:suhaib / :marco]]

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

Comment 4

[BugBot [:suhaib / :marco]]

The bug has a release status flag that shows some version of Firefox is affected, thus it will be considered confirmed.

Comment 5

[Hiroyuki Ikezoe (:hiro)]

It looks like this is one of symptoms of reverse checkerboarding.

Comment 6

[farblos]

Out of boredom I retried than (in a similar setting as originally filed) on FF 128.14.0esr.

Cannot reproduce the original issue on that version.