Bug 510522

Summary:	Can no longer change resolution of attached projector independent from internal laptop display
Product:	[Plasma] KScreen	Reporter:	Kevin Krammer <krammer>
Component:	common	Assignee:	kscreen-bugs-null <kscreen-bugs-null>
Status:	RESOLVED INTENTIONAL
Severity:	normal	CC:	nate, xaver.hugl
Priority:	NOR
Version First Reported In:	6.4.5
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Kevin Krammer 2025-10-12 09:01:46 UTC

SUMMARY

KScreen seems to have lost the ability to switch resolution of outputs independently.

I am teaching various programming courses and one of KScreen's killer features of any competitor has been the ability to share the laptop screen with a projector at different resolution.

This allows the presenter to interact with the laptop like you would when having no projector attached while at the same time having "private" space not shared with the projector.

Lecturers with less advanced systems need essentially a third monitor so that they can sit in front of the same content as the projection yet still have one monitor for their speaker notes, etc.

STEPS TO REPRODUCE
1. Attach a monitor or projector to a laptop (or a PC with an already configured monitor)
2. In KScreen's configuration screen choose to mirror/clone/replicate the internal screen onto to external one
3. Select the external one in the comboboc
4. Change the resolution of the external monitor to be less than that of the internal one

OBSERVED RESULT

Resolution of the internal screen also switched to the new resolution

EXPECTED RESULT

Only resolution of the selected monitor (projector) changes, resulting in only the overlapping top-left portion of the internal screen's content to be also visible on the external display.

SOFTWARE/OS VERSIONS

K_API_VERSION_1_0 [VUID-VkApplicationInfo-apiVersion]
Operating System: KDE neon User Edition
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.14.0-33-generic (64-bit)
Graphics Platform: X11

ADDITIONAL INFORMATION

Worked flawlessly since Plasma 5, probably even longer.
Last observed working before the 2025 summer holidays,likely Plasma 6.3.5,

Might be possible to work around this regression using xrandr, will report back once I had a chance to try this

Comment 1 Nate Graham 2025-10-13 19:15:54 UTC

IIRC this was intentional; CCing the person who my memory says might know,

Comment 2 Kevin Krammer 2025-10-14 07:36:07 UTC

I thought only manually dragging one screen on top of the other got disabled as this could lead to weirdly misaligned coverage.

"clone and resize" avoids that and is super quick to set up.

Comment 3 Zamundaaa 2025-10-14 15:59:55 UTC

Cloning is definitely only meant for actual cloning. If you want to replicate the setup you describe, for now you'll have to use the command line (kscreen-doctor).

Properly supporting the use case might be interesting though; I remember someone telling me they used OBS's preview of recording the projector screen to do something similar. Replicating something in that direction with nicer UX could be cool.

Comment 4 Kevin Krammer 2025-10-15 12:46:51 UTC

Thank you for the tip regarding kscreen-doctor, will have to experiment with this as soon as I get a chance.

I also heard about using OBS instead but haven't been able to find time to learn it.
Might also be a bit too much for my old laptop :)

The great thing about the "partial cloning" approach was that it worked out of the box with almost no input.
In earlier versions an alternative was to drag the other output "on top" of the internal one but you could easily end up with some accidental offset.