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Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors?

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On 2025-12-26, John-Paul Stewart <jpstewart@personalprojects.net> wrote:
> On 2025-12-24 11:15 p.m., Robert Riches wrote:
>> 
>> Does anyone have favorite tutorials or other helps for dealing
>> with a high-DPI transition?
>> 
>> I'm Running Devuan (currently Daedalus, hopefully soon Excalibur)
>> using plain X and fvwm2, no DE as such with 1920x1200 monitors.
>> Just purchased a round of 4k monitors, so I'll be needing to
>> adjust xterm fonts, web browser issues, other GUI application
>> issues, etc.
>
> It's been a couple years since made a similar switch.  But as far as I
> recall, there's not much to do other than configuring X.  I had to
> manually specify the monitors' physical size (in millimetres) in my
> xorg.conf so that X could calculate the correct DPI.  Then everything
> that's measured in points just kind of fell into place.  (E.g., there
> was nothing to be done for LibreOffice, etc.)

After waiting for adapters to arrive (by "super saver" shipping)
and getting the 1.1GB system logs after physically installing the
4K monitors, I got them running at 1920x1200 by putting
"xrandr --output ... --mode 1920x1200" and a couple of sleep
commands in my .Xclients file.  Omitting the xrandr commands
brings up X in 3840x2160 mode, but the DPI is stuck at 96.

Xorg.0.log showed the EDID size information being fetched correct
as 597 x 336 mm.  However, Xorg.0.log showed the DPI being set to
(96, 96).

So, I created an xorg.conf.  Evidently, X11 wants things
specified in terms of two monitors side by side--thus the 1194 by
336.  After some experimenting, I put this in /etc/X11/xorg.conf:

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv cut here vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
Section "Screen"
  Identifier "Default Screen Section"
  Monitor "Asus PA279CV"
EndSection

Section "Monitor"
  Identifier "Asus PA279CV"
  VendorName "Asus"
  ModelName "PA279CV"
  DisplaySize 1194 336
EndSection
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cut here ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

With that, grepping /var/log/Xorg.0.log for words EDID, mm, and
DPI yields this:

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv cut here vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
[179297.003] (II) AMDGPU(0): EDID for output DisplayPort-0
[179297.003] (II) AMDGPU(0): EDID Version: 1.3
[179297.003] (II) AMDGPU(0): clock: 594.0 MHz   Image Size:  597 x 336 mm
[179297.003] (II) AMDGPU(0): clock: 148.5 MHz   Image Size:  597 x 336 mm
[179297.003] (II) AMDGPU(0): clock: 297.0 MHz   Image Size:  597 x 336 mm
[179297.003] (II) AMDGPU(0): clock: 241.5 MHz   Image Size:  597 x 336 mm
[179297.003] (II) AMDGPU(0): Number of EDID sections to follow: 1
[179297.003] (II) AMDGPU(0): EDID (in hex):
[179297.006] (II) AMDGPU(0): EDID for output DisplayPort-1
[179297.006] (II) AMDGPU(0): EDID Version: 1.3
[179297.007] (II) AMDGPU(0): clock: 594.0 MHz   Image Size:  597 x 336 mm
[179297.007] (II) AMDGPU(0): clock: 148.5 MHz   Image Size:  597 x 336 mm
[179297.007] (II) AMDGPU(0): clock: 297.0 MHz   Image Size:  597 x 336 mm
[179297.007] (II) AMDGPU(0): clock: 241.5 MHz   Image Size:  597 x 336 mm
[179297.007] (II) AMDGPU(0): Number of EDID sections to follow: 1
[179297.007] (II) AMDGPU(0): EDID (in hex):
[179297.007] (II) AMDGPU(0): EDID for output DisplayPort-2
[179297.007] (II) AMDGPU(0): EDID for output HDMI-A-0
[179297.007] (**) AMDGPU(0): Display dimensions: (1194, 336) mm
[179297.007] (**) AMDGPU(0): DPI set to (163, 163)
[179297.465] (II) event6  - Logitech Trackball: device set to 300 DPI
[179297.561] (II) event6  - Logitech Trackball: device set to 300 DPI
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cut here ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The (163, 163) is the correct DPI figure.  An earlier DisplaySize
value of 597 336 had yielded a DPI figure of (326, 163).  With
either of the DisplaySize values, and even with Xorg.0.log
showing the correct DPI, xdpyinfo still reports DPI as 96x96.

So, it appears that even when Xorg.0.log is showing the correct
DPI, but there's apparently a disconnect between that and
xdpyinfo.

Any suggestions?  Thanks in advance!

-- 
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)

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Thread

[On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-25 04:15 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? The Natural Philosopher <tnp@invalid.invalid> - 2025-12-25 11:45 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-26 02:03 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2025-12-25 21:38 -0500
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-26 03:55 +0000
      Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2025-12-26 11:10 -0500
        Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-31 05:00 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? c186282 <c186282@nnada.net> - 2025-12-26 00:03 -0500
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-15 05:09 +0000
      Xorg drivers overriding display resolution (was: Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors?) Nuno Silva <nunojsilva@invalid.invalid> - 2026-01-15 11:20 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-21 22:54 +0000
      Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Nuno Silva <nunojsilva@invalid.invalid> - 2026-01-22 10:09 +0000
        Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2026-01-22 09:34 -0500
          Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-23 04:23 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? c186282 <c186282@nnada.net> - 2025-12-26 00:00 -0500

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