1737715 - Firefox scales incorrectly when next to a hidpi screen on Wayland

Status: RESOLVED MOVED

(Core :: Widget: Gtk, defect, P3)

Description

[Jarrad Whitaker]

Attachment: firefox.excerpts.log

User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4464.5 Safari/537.36

Steps to reproduce:

For context, I'm using Firefox in Wayland mode with Gnome Shell 40 as my compositor (stock Pop OS / Ubuntu 21.10).

I have three screens -
[ laptop internal ] [ Dell 1 , 1920x1200 ], [ Dell 2, 1280x1024]

laptop internal is High DPI, set to 200% scaling with fractional scaling disabled in wayland. Dell 1 and Dell 2 are 100% scaling. Dell 1 is my primary.

When Firefox is on the laptop internal display, it scales at 2× correctly.
When Firefox is on the Dell 2 display, it scales at 1× correctly.
When Firefox is on the right side of the Dell 1 display, it scales at 1× correctly.
These are all fine.
However, when Firefox is on the left side of the Dell 1 display, it scales roughly correctly (widgets are the right size visually), but text becomes a bit blurry and it gets a little bit slower when scrolling etc. I believe it's rendering at 2× and getting scaled down to 1× at some point.

I've attached a full log with Widget:5 debug, and also some excerpts annotated with me moving windows

• start on internal (ok)
• move to left of dell 1 (blurry problem here)
• move to right of dell 1 (ok)
• move back to left of dell 1 (blurry)
• move to dell 2 (ok)

When I say "left of", "right of", I'm tiling my windows so that firefox takes up roughly half the screen. My tiler adds a margin of 2-4pixels or so, so Firefox is not at the very edge of the screen in these cases, it's inset a little bit (so likely this is more an off by >1 error than an off by 1 error ;) ).

This seems to support my theory that Firefox is getting rendered at 2× when on the left of Dell 1, and scaled down to 1× in some post step somewhere (firefox, gnome shell, who knows) that hides the problem.

Expected results:

Firefox should not be blurry when it's next to the HiDPI display.

Comment 1

[Jarrad Whitaker]

Attachment: ff on left, blurry.png

Comment 2

[Jarrad Whitaker]

Attachment: ff on right, good.png

Comment 3

[Jarrad Whitaker]

Attachment: firefox.drag-between-margin.log

Here is another way to show the problem - here, firefox is in windowed mode and I'm dragged it so the left edge is on either side of about X=10 or so on the left edge of Dell 1. If the left edge of FF is on the right of this line we get Scale=1, if it's on the left we get Scale=2.

This log shows output when I drag back and forth over this invisible line.

Comment 4

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

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

Comment 5

[Martin Stránský [:stransky] (ni? me)]

You may see https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/3941 - gdk sends wrong scales.

Try latest nightly:
https://fedoraproject.org/wiki/How_to_debug_Firefox_problems?rd=Bug_info_Firefox#Testing_Mozilla_binaries
tun on terminal and unset XDG_CURRENT_DESKTOP env variable.

i.e. run something like:

XDG_CURRENT_DESKTOP="none" MOZ_ENABLE_WAYLAND=1 ./firefox

(but that introduces scaling issues on Gnome as it sends wrong screen sizes). So generally wait until https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/3941 hits stable.

Comment 6

[Jarrad Whitaker]

Nah in the meantime I realized it actually affects all GTK apps as well, I just noticed the text rendering in Firefox before I saw it in Gnome Terminal :)
Raised upstream at https://gitlab.gnome.org/GNOME/gtk/-/issues/4372 (well.. i tested with Gtk4 actually which I'm guessing Firefox isn't using, but the behaviour is identical)
Will check nightly in a bit just in case though.

Comment 7

[Martin Stránský [:stransky] (ni? me)]

Okay, moving then.