X11 to Wayland : how can I use "scaled" aspect ratio?

Help
,
1

Hello,

I hope someone will be able to help me.

I’m on KUbuntu 26.04 LTS on a X11 session, with KDE Plasma 6.6.4.
I use two screens. My first screen is an AOC 2560x1440 panel @ 180Hz max , my second screen is a SAMSUNG 2560x1440 panel @ 144Hz max.
My video card is an AMD RX9070XT PULSE from Sapphire. I use the free software driver.

The “problem” is that the SAMSUNG is one to two centimetres taller than the AOC.
I don’t want to replace my Samsung panel. It works well despite some flaws, and the AOC panel is no longer buyable anyway.

In order to alleviate the fact that my screens have not the same height, on a X11 session, I use this command :
xrandr --fb 5120x1440 --output DisplayPort-0 --auto --primary --mode 2560x1440 --rate 144 --pos 0x0 --output DisplayPort-1 --auto --mode 2560x1440 --rate 144 --left-of Displ
ayPort-0 --scale 1x0.970

The key here is the “–scale 1x0.970”.
With this, my second screen is “only” 2560x1397 in spite of 2560x1440, but it allows :

  • windows that are large enough to be on the two screens, to seem to be almost the same height => they are almost “scaled” to the same height
  • to have texts, that are on those windows, almost aligned across the screens => I can read them

Some purists would certainly thinks it would deform the windows and render blurry texts, and it is certainly true, but… all in all, it’s way better than the unscaled windows and shifted texts !
It works very well, I can assure you of this.

Alas, on Wayland (on KUbuntu 16.04 or CachyOS), with the default screen management, I can’t read text across the two screens because of the offset (and - not that it matters here - but I have the same problem on my dual-boot Windows 11).

But X11 is dying and I want to test CachyOS with Wayland to be able to use FreeSync and HDR, so that’s why I’m here asking for your help.

Is there an equivalent of xrandr in wayland that would allow me to do the same thing as the xrandr command I use with X11 ?
Or better, perhaps is there something I can do with some KDE Plasma utils rather than bypassing the configuration tool like I do on X11 ?

Thank you.

2

Have you tried the scale setting in System Settings? Wayland and Plasma supports fractional scaling.

image
image2122×2262 280 KB

3

Yeah I don’t see why it wouldn’t work. It’s what I do with my current setup. My left screen has a scale of 0.95 to adjust for the height differences.

4

Hello,

I can’t test it right now, but thank you Landing1979 and maledict, for the tip.
I recall having tested this option one month ago but I failed at that time to achieve what I wanted.
What should I enter : 97% (in my case) ?

I have one remark before testing : it seems this parameter would be equivalent to --scale 0.97x0.97 and not my previous --scale 1x0.97 => this parameter will change the height AND the width of the screen.
This should be better in term of aspect ratio, so I’m not complaining in advance.
And I hope it will scale only one screen, and not the two.

I will let you know.

5

Hello,

I have tested the scale option in the display control panel on CachyOS.

I successfully managed to scale my Samsung Screen with a 103.33% screen ratio and, even if I can’t choose the exact scale myself, I can perfectly live with this.
Thank you Landing1979 and maledict.

Why didn’t I see it before :

  • the little arrows to change the value of the scale sometimes are clickable, sometimes not (why !?)
  • and when they are clickable, they change the value by 5% => so I didn’t try to change the value myself.

Good thing : I have restarted my PC and the scale was preserved !
Strange thing : the scale value is now 101.67% => I think it’s clearly not, it’s certainly 103.33%, but to be sure it would require that I knew the actual resolution but I used xrandr on KUbuntu so I don’t know how to do it CachyOs for Wayland.

One more time, thank you Landing1979 and maledict.

6

That’s for complicated reason, we can’t have scale factors such as 103.3333333 that will cause all sorts of problems.
The fractional scaling protocol restricts the values to factor of 120, so that apps can round things better.
And that’s complicated to surface to the user…