Bug 440661

Summary: Syncing DPI results in annoying extra steps after changing scale factor globally
Product: [Applications] systemsettings Reporter: Armando Ota <armando.ota>
Component: kcm_sddmAssignee: David Edmundson <kde>
Status: CONFIRMED ---    
Severity: normal CC: kde, nate, plasma-bugs
Priority: NOR    
Version: 5.22.4   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:

Description Armando Ota 2021-08-06 11:49:31 UTC 
SUMMARY
I changed global scale in display configuration to 125%. Rebooted. After a test I changed it back to 100%. Rebooted. 
Then the problems occured. 
SDDM login screen and KDE apps did not change scale back to 100%. After googling I found out that I had to froce fonts DPI size to 96 and add following lines to /etc/sddm.conf 
[XDisplay]
ServerArguments=-dpi 96
to make things as they were.  

STEPS TO REPRODUCE
1. Display settings > Change global scale to 125%
2. Press APPLY
3. REBOOT
4. Login 
5. Display settings > Change global scale to 100%
6. Press APPLY
7. REBOOT

OBSERVED RESULT
everything is still scaled up!

EXPECTED RESULT
default as before 125% global scale shange

SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.22
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.84.0
Qt Version: 5.15.3
Kernel Version: 5.11.0-25-generic (64-bit)
Graphics Platform: X11
Processors: 12 × Intel® Core™ i7-8086K CPU @ 4.00GHz
Memory: 31,3 GiB of RAM
Graphics Processor: GeForce GTX 1060 3GB/PCIe/SSE2

ADDITIONAL INFO: 

I've got 3 monitors setup with 2 of them 2560x1600 resolution and 1 monitor with 2560x1440 resolution
Comment 1 David Edmundson 2021-08-06 12:35:18 UTC 
Had you run system settings -> login screen -> sync settings?

If you run that again does that resolve it?
Comment 2 Armando Ota 2021-08-06 12:59:36 UTC 
I can confirm.
Removing 
[XDisplay]
ServerArguments=-dpi 96
from sddm.conf 
and system settings -> login screen -> sync settings did help to reset SDDM layout.
Comment 3 David Edmundson 2021-08-06 13:17:34 UTC 
I think the best thing would be to avoid syncing that setting, as it has a knock on effect on the dekstop and instead manually insert a QT_SCALE_FACTOR into the env of the greeter.
Comment 4 Nate Graham 2021-08-06 16:53:43 UTC 
No objection to that, as long as it can read the correct scale factor before the user session has started.