Arch & Gnome scale factor differences between eDP1 and HDMI1

kobhian · 2021-02-25 21:38:33

Hello,

I have both a laptop and a computer running 4K screens, yet the way Arch identifies and support HiDPI on these devices is completely different.

Laptop - eDP1 connection - scale factor alone provides native support for this resolution, no need to use xrandr/scale factor tweaks to achieve a comfortable resolution (200%)
Computer - HDMI-1 connection - I have to use xrandr to scale to 1.5x making the UI smaller enough to be followed by defining a scale factor of 200% in order to get a comfortable resolution.

I get the same result with both methods, so what's the problem?

Scaling through xrandr renders performance slower.

What's the reasoning behind this?

Thanks in advance.

Lone_Wolf · 2021-02-26 11:55:11

I get the same result with both methods, so what's the problem?

You tell us, maybe the screens just have different properties ?
please post xrandr -q from both .

Are both systems using Gnome and Xorg ?

The wiki text about xorg fractional scaling is somewhat ambiguous, but to me indicates you should configure xrandr / gnome scale in a different order :

First scale GNOME up to the minimum size which is too big. Usually "2" is already too big, otherwise try "3" etc.
Then start scaling down by setting zoom-out factor with xrandr

kobhian · 2021-02-28 18:31:51

Hello Lone_Wolf,

Sorry for the confusion, indeed, at boot Gnome will first set scale factor to 200% and only then my xrandr script kicks in setting the scale factor.

xrandr -q

Desktop (4K Screen connected through HDMI)

Screen 0: minimum 8 x 8, current 5760 x 3240, maximum 32767 x 32767
DVI-D-0 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 connected primary 5760x3240+0+0 (normal left inverted right x axis y axis) 600mm x 340mm
   3840x2160     60.00*+  59.94    50.00    30.00    29.97    25.00    23.98    23.98  
   2560x1440    120.00  
   1920x1080    119.88    60.00    59.94    50.00    29.97    23.98  
   1280x720      59.94    50.00  
   1024x768      60.00  
   800x600       60.32  
   720x576       50.00  
   720x480       59.94  
   640x480       59.94    59.93

Laptop (4K screen)

Screen 0: minimum 8 x 8, current 3840 x 2160, maximum 32767 x 32767
eDP1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 310mm x 170mm
   3840x2160     60.00*+
   3200x1800     59.96    60.00    59.94  
   2880x1620     60.00    59.96    59.97  
   2560x1600     59.99    59.97  
   2560x1440     59.96    60.00    59.95  
   2048x1536     60.00  
   1920x1440     60.00  
   1856x1392     60.01  
   1792x1344     60.01  
   2048x1152     60.00    59.90    59.91  
   1920x1200     59.88    59.95  
   1920x1080     59.96    60.00    59.93  
   1600x1200     60.00  
   1680x1050     59.95    59.88  
   1400x1050     59.98  
   1600x900      60.00    59.95    59.82  
   1280x1024     60.02  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1368x768      60.00    59.88    59.85  
   1280x800      59.81    59.91  
   1280x720      59.86    60.00    59.74  
   1024x768      60.00  
   1024x576      60.00    59.90    59.82  
   960x540       60.00    59.63    59.82  
   800x600       60.32    56.25  
   864x486       60.00    59.92    59.57  
   640x480       59.94  
   720x405       59.51    60.00    58.99  
   640x360       59.84    59.32    60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Thank you!

Last edited by kobhian (2021-02-28 18:33:04)

Lone_Wolf · 2021-03-01 15:49:12

eDP1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 310mm x 170mm

HDMI-1 connected primary 5760x3240+0+0 (normal left inverted right x axis y axis) 600mm x 340mm

The eDP1 screen does match with a 4k resolution UHD screen, the HDMI screen would probably be described as a 6k resoltion screen[1]
It's not surprising they need different values.

The scaling needed for the hdmi screen appears to be a fractional scaling, which is not possible for gnome scaling on xorg without the help of xrandr .

If you were using gnome on wayland, you could use fractional scaling.
Another alternative might be to remove/reset gnome and Xrandr scaling and try setting correct DPI in Xresources using Xft.dpi [2].

[1] There doesn't appear to be an official 6k resolution, but if there was 5760x3240 would be it's consumer version .
[2] https://wiki.archlinux.org/index.php/HiDPI#X_Resources

kobhian · 2021-03-02 15:47:47

Lone_wolf,

Apologies, I took the

xrandr -q

with the xrandr scale applied by default, which ofc results in that resolution, here's the proper, non scaled, default screen specs:

Screen 0: minimum 8 x 8, current 3840 x 2160, maximum 32767 x 32767
DVI-D-0 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 600mm x 340mm
   3840x2160     60.00*+  59.94    50.00    30.00    29.97    25.00    23.98    23.98  
   2560x1440    120.00  
   1920x1080    119.88    60.00    59.94    50.00    29.97    23.98  
   1280x720      59.94    50.00  
   1024x768      60.00  
   800x600       60.32  
   720x576       50.00  
   720x480       59.94  
   640x480       59.94    59.93

Lone_Wolf · 2021-03-03 12:36:27

So both screens are 4k 3840x2160 resolution, they just have different physical size / DPI values .
The HDMI screen appears to be twice as big as the laptop screen .

The rest of post #4 seems appropriate, but I'll try to rephrase it to make it clearer.

Your screens need different settings and your options are limited because of choices made by gnome / xorg / wayland developers.
Those choices are the same for any linux distro.

The laptop screen is set to use a gnome setting, the hdmi screen needs that setting plus a xrandr command.
Both methods only work on xorg .

Switching both screens to gnome wayland should allow them to use another gnome specfic setting that works for both screens, but only under wayland .[1]

Another option is to make sure gnome does not adjust anything and rely on Xorg settings instead.
Setting Xft.dpi in ~/.Xresources seems the best way to do this.

[1] How well gnome on wayland / Xwayland works for you depends on the hardware / driver.
with amd / intel opensource drivers it should work fine, with nvidia proprietary driver it won't .

kobhian · 2021-03-03 13:06:56

Excelent, you do make a lot of sense, yes, never considered physical size to have an impact on this setting, hehe.

I'd love to go wayland but indeed, my computer is powered by Nvidia, so it's not possible (yet).

I'll play with Xresource and let you know

Thanks!!

Arch Linux

#1 2021-02-25 21:38:33

Arch & Gnome scale factor differences between eDP1 and HDMI1

#2 2021-02-26 11:55:11

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

#3 2021-02-28 18:31:51

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

#4 2021-03-01 15:49:12

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

#5 2021-03-02 15:47:47

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

#6 2021-03-03 12:36:27

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

#7 2021-03-03 13:06:56

Re: Arch & Gnome scale factor differences between eDP1 and HDMI1

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