Bug 501346

Summary:	KCM reports impossible and wrong configurations, making it very difficult to deal with multi-monitor setups
Product:	[Applications] systemsettings	Reporter:	Riccardo Robecchi <sephiroth_pk>
Component:	kcm_kscreen	Assignee:	kscreen-bugs-null <kscreen-bugs-null>
Status:	CONFIRMED ---
Severity:	major	CC:	kdedev, nate, plasma-bugs-null, xaver.hugl
Priority:	NOR	Keywords:	multiscreen
Version First Reported In:	6.3.2
Target Milestone:	---
Platform:	Neon
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	Screenshot of the KCM in an inconsistent state Invalid KCM state for external monitor

Description Riccardo Robecchi 2025-03-11 10:35:22 UTC

Created attachment 179293 [details]
Screenshot of the KCM in an inconsistent state

SUMMARY
With multi-monitor setups, the KCM reports patently absurd screen configurations that make no sense whatsoever. As an example, see the screenshot: there are three monitors (one is the laptop's), and one is enabled but not correctly displayed so it can't be dragged nor interacted with. The KCM does not enable the "apply" button if I change the mirroring (so it stays disabled whether I make it mirror the laptop's screen, or whether I don't). The whole thing is inconsistent to the point I cannot understand what is going on.

I suspect this might be related to bug 466297, as this situation arises when the laptop screen is disabled (e.g. if I close the lid, or if the system boots with the lid closed).
In any case, this makes it extremely frustrating to use Plasma as it requires 10+ minutes of troubleshooting every time.

STEPS TO REPRODUCE
1. Use a laptop with a multi-screen setup
2. (maybe) mirror your laptop's screen to another monitor

OBSERVED RESULT
The KCM reports wrong, inconsistent and/or impossible configurations, and behaves erratically.

EXPECTED RESULT
The KCM reports the actual state and allows you to modify it.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE Neon
KDE Plasma Version: 6.3.2
KDE Frameworks Version: 6.11.0
Qt Version: 6.8.2

ADDITIONAL INFORMATION

Comment 1 TraceyC 2025-03-11 17:23:36 UTC

I was easily able to reproduce an invalid KCM state with Plasma 6.3.2

Setup:
Laptop connected to a dock, with 2 external monitors attached (monitors 1 and 2)
Original configuration: No mirrored displays. Monitor 1 set to top priority, laptop 2nd, monitor 2 last priority

STEPS:
In the Display Configuration, change monitor 1 to be a replica (mirror) of the built-in screen, Apply
Change it back to be a replica of none, Apply

Result: there is text but no rectangle around monitor 1 in the KCM (see screenshot)
I had to disable the screen, apply, re-enable and apply again to allow the system to use all 3 displays as in the original setup

Comment 2 TraceyC 2025-03-11 17:25:05 UTC

Created attachment 179311 [details]
Invalid KCM state for external monitor

No rectangle around monitor 1 in the KCM, only text, KCM reports displays not touching.