1767142 - [wayland] Implement fractional-scale-v1 protocol support for fractional scaling

Status: RESOLVED FIXED

(Core :: Widget: Gtk, enhancement)

Description

[Robert Mader [:rmader]]

The new protocol (still draft) at https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3511 allows compositors to tell us the optimal fractional scale to use with the already existing fractional scaling implementation (currently using the about:config value widget.wayland.fractional_buffer_scale). Having Firefox builds should help with the upstreaming process.

Should not be merged until the protocol is upstreamed.

Comment 1

[Robert Mader [:rmader]]

Attachment: WIP: Bug 1767142 - [wayland] Implement fractional-scale-v1 protocol support

Comment 2

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

The bug assignee is inactive on Bugzilla, so the assignee is being reset.

Comment 3

[Suhaib Mujahid [:suhaib]]

Sorry, there was a problem with the detection of inactive users. I'm reverting the change.

Comment 5

[Robert Mader [:rmader]]

The protocol landed now, see https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/4624cfaaf563cd7be5e2e2087c8de6d3a48ea867/staging/fractional-scale/fractional-scale-v1.xml

Hope to get around to implement this soon.

Comment 6

[Robert Mader [:rmader]]

Just updated the patch - it should work now if you use a compositor supporting the protocol (minus bugs). The about:config switch changed to a simple widget.wayland.fractional-scale.enabled bool.

Will need a bit more refining, then we should be able to land it.

Comment 7

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

Robert, how is that integrated with our current Gtk code? AFAIK Gtk uses fixed scales (1,2,3..) and then the frame buffer is scaled by compositor, right? So we paint only the fixed scales to the surfaces. So is there any benefit here or does it help somehow?

Comment 8

[Robert Mader [:rmader]]

(In reply to Martin Stránský [:stransky] (ni? me) from comment #7)

Robert, how is that integrated with our current Gtk code? AFAIK Gtk uses fixed scales (1,2,3..) and then the frame buffer is scaled by compositor, right? So we paint only the fixed scales to the surfaces. So is there any benefit here or does it help somehow?

This would be independent from GTK. As we create/control the (subsurface) buffer ourselves, we can use this protocol and vp_viewporter to determine an optimal buffer size which is both more performant and and many cases also sharper.

Quick example of bandwidth on a 1920x1080 @ 125% screen. The number of pixels painted on a fullscreen repaint:

1. integer scaling: (1536 x 2) x (864 x 2) = 5308416
2. fractional scaling: 1920 x 1080 = 2073600

2073600 / 5308416 = 0,390625 -> 60% reduction in pixel painted.

125% (and smaller values) are the most extreme though.

Comment 9

[[object Object]]

KDE does actually allow you to pick a value as low as 105%

Comment 10

[Hugo Osvaldo Barrera]

The fractional_scale_v1 protocol has been stabilised and released in wayland-protocols 1.32.

A few compositors already have support, albeit no stable releases yet.

Comment 11

[equeim]

A few compositors already have support, albeit no stable releases yet.

It was released in Plasma 5.27, no?

Comment 12

[[object Object]]

(In reply to equeim from comment #11)

A few compositors already have support, albeit no stable releases yet.

It was released in Plasma 5.27, no?

Yeah, it was

Comment 13

[Robert Mader [:rmader]]

It's also supported in Gnome 44.

Comment 14

[[object Object]]

So mast of the Linux desktop space has support then

Comment 15

[[object Object]]

*most (wish this site had an edit feature...)

Comment 16

[Emilio Cobos Álvarez (:emilio)]

Robert, do you have any plans to rebase and maybe land the patch? I think having it in-tree at least in an experimental fashion would be good.

Alternatively I can try to poke. I added support for drawing scaled-down GTK widgets a while ago so I don't think the gtk integer scale would be an issue, necessarily.

Comment 17

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

wp_fractional_scale_manager_v1 seems to be present on Gnome/Fedora 38.

Comment 18

[Robert Mader [:rmader]]

(In reply to Emilio Cobos Álvarez (:emilio) from comment #16)

Robert, do you have any plans to rebase and maybe land the patch? I think having it in-tree at least in an experimental fashion would be good.

Would love to, but unfortunately I'm quite busy (with related work in Mutter) atm :(

Alternatively I can try to poke. I added support for drawing scaled-down GTK widgets a while ago so I don't think the gtk integer scale would be an issue, necessarily.

Would love to see that!

Comment 19

[Emilio Cobos Álvarez (:emilio)]

Ok, let me add it to my queue of things to poke at when I have the time :)

Comment 20

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1767142 - [gtk] Simplify MozContainer state tracking. r=stransky,rmader

Use C++ constructor/destructors to deal with MozContainer state, which makes
stuff a bit simpler to reason about, and a bit more correct.

For example we were relying on an std::vector<> allocated via calloc() being
correct, which seems to hold but it's UB and a bit sketchy.

Comment 21

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1767142 - [wayland] Implement fractional-scale-v1 protocol support for fractional scaling. r=stransky,rmader

This is a manually-rebased version of D145169, but with the protocol
header regenerated, various fixes and tweaks.

In particular we only check the pref once when asking for the protocol
now, the rest falls through from current_fractional_scale being 0.0.

I gave it a shot on KWin and stuff seems to work properly, but let's
keep it disabled by default for now and maybe enable on a separate bug.

Depends on D186198

Comment 22

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1918c42903e1
[gtk] Simplify MozContainer state tracking. r=stransky
https://hg.mozilla.org/integration/autoland/rev/9c5926a01415
[wayland] Implement fractional-scale-v1 protocol support for fractional scaling. r=stransky
https://hg.mozilla.org/integration/autoland/rev/0d76ff7134f6
apply code formatting via Lando

Comment 23

[Narcis Beleuzu [:NarcisB]]

Backed out for nsTArray_base crashes

Backout link: https://hg.mozilla.org/integration/autoland/rev/e20f92633534c049eecb9e49bf7860cd506b2abf
Log link: https://treeherder.mozilla.org/logviewer?job_id=426018935&repo=autoland&lineNumber=6648

Comment 24

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/13a48c068860
[gtk] Simplify MozContainer state tracking. r=stransky
https://hg.mozilla.org/integration/autoland/rev/c01858a20255
[wayland] Implement fractional-scale-v1 protocol support for fractional scaling. r=stransky
https://hg.mozilla.org/integration/autoland/rev/c97a1a56c617
apply code formatting via Lando

Comment 25

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/13a48c068860
https://hg.mozilla.org/mozilla-central/rev/c01858a20255
https://hg.mozilla.org/mozilla-central/rev/c97a1a56c617