Bug 500495

Summary: Applying screen layout (desktop configuration) and desktop backgrounds to the login screen (SDDM) does not take effect
Product: [Applications] systemsettings Reporter: incansvl
Component: kcm_sddmAssignee: Plasma Bugs List <plasma-bugs-null>
Status: RESOLVED UPSTREAM    
Severity: normal CC: kde, kde, natalie_clarius, nate
Priority: NOR    
Version First Reported In: 6.3.0   
Target Milestone: ---   
Platform: Neon   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description incansvl 2025-02-20 23:07:15 UTC 
SUMMARY
I am logged in as a user with membership of the sudo and admin groups

My machine has 3 monitors in a "PLP (portrait-landscape-portrait) configuration, so screen config is important for the machine to be usable

However changes to the SDDM desktop config and style do not "stick". After logout the login display uses the default background wallpaper and screen config, leaving 2 out of 3 monitors with displays rotated by 90 degrees 

STEPS TO REPRODUCE
1. Set a custom Display Configuration and "Desktop and Wallpaper"
2. Open the "Login Screen (SDDM)" system setting
3. Select "Apply Plasma Settings"

OBSERVED RESULT
One of the default desktop themes, with no customisation of the screen config (i.e. screen position and rotation) is applied


EXPECTED RESULT
On this config page, there are selection icons for a couple of default configurations (Breeze and Maya), plus an "Apply" button at the bottom of the page.

I would expect selecting one of the default themes and hitting "Apply" would set SDDM to use that theme. The fact tat the default themes don't handle things liek screen rotation is annoying, but not surprising.

However, given that the "Apply" button exists to apply a selected theme, my expectation was that the "Apply Plasma Settings" button was clearly there for a different purpose, otherwise it would be redundant.

What I expected it to do was apply MY CURRENT PLASMA SETTINGS (theme colours, wallpapers, AND screen configuration) to SDDM, so that having spent the time to set up a "sane" desktop config on my account, I could easily apply it the login environment.

(Note, if the user needs to authenticate as sudo to alter the config of SDDM, there should be a popup asking for authentication like other admin changes)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE Neon 6.2
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.2

ADDITIONAL INFORMATION
Comment 1 incansvl 2025-02-24 17:24:48 UTC 
I did some digging into how this is supposed to work. I found that the configuration data for my personal login, at least for the physical aspects of screen resolutions, positions, and rotations (not sure how theme info works) that is stored in `/var/lib/sddm/.config/kwinoutputconfig.json` IS being writtem to the SDDM config file in `/var/lib/sddm/.config/kwinoutputconfig.json`

If this is all that needs to be done, then it appears the KDE settings tool is doing what it's supposed to do, but SDDM is ignoring the rotation settings.

If someone can confirm that updating `/var/lib/sddm/.config/kwinoutputconfig.json` is all that's required, then I think this is an issue withj SDDM. It can be closed here and I will report it to the SDDM team.
Comment 2 Nate Graham 2025-02-26 19:05:57 UTC 
That is correct. Good work!