1824552 - [wayland] Use ScreenGetterGtk on Gnome with fractional scaling

Status: RESOLVED FIXED

(Core :: Graphics, task)

Description

[Robert Mader [:rmader]]

On Wayland there are two common ways to implement scaling:

1. Integer-only scaling, compatible with Xwayland HiDPI clients. This is used on Gnome by default
2. Fractional scaling. This is used by default by all other common Wayland compositors, as well as on Gnome if fractional scaling is enabled (scale-monitor-framebuffer experimental setting).

For 1. there's a special ScreenGetterWayland implementation that is used instead of ScreenHelperGTK on Gnome. Lets try to detect when Mutter is running with fractional scaling enabled and use ScreenHelperGTK in that case.

Comment 1

[Robert Mader [:rmader]]

P.S.: this, among other things, fixes wrongly sized popups on Gnome with fractional scaling.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

I think we should just do this unconditionally, see bug 1753601 (and bug 1753601 comment 48 in particular)...

Comment 3

[Robert Mader [:rmader]]

Oh, are you sure ScreenGetterGTK works correctly for Gnome without fractional scaling? If so - awesome!

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1824552 - Move ScreenHelper implementation details to the cpp file. r=stransky,rmader

Comment 5

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1824552 - Remove ScreenGetterWayland. r=stransky

This fixes screen sizes when using mutter with fractional scaling, and
shouldn't change behavior otherwise.

Without this patch, mutter with scale at 150% reports:

[screen.width, screen.height] == [ 1920, 1080 ]

With this it reports the proper [ 2560, 1440 ].

The bug that caused us to introduce it was long fixed in gtk itself, as
I understand it, and ScreenGetterGtk is also what's used everywhere else
on Wayland.

Re-implement GetScreenForWindow in a way that works for ScreenGetterGtk
too, to avoid regressing any functionality on mutter.

Depends on D186341

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3b3db7c9f72b
Move ScreenHelper implementation details to the cpp file. r=stransky
https://hg.mozilla.org/integration/autoland/rev/3b5a0c666d81
Remove ScreenGetterWayland. r=stransky

Comment 7

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/3b3db7c9f72b
https://hg.mozilla.org/mozilla-central/rev/3b5a0c666d81