Bug 441460

Summary:	When enabling second display with lower resolution than primary display, second monitor has visual defects even at matching/correct resolution
Product:	[Plasma] kwin	Reporter:	kderemie
Component:	multi-screen	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	kderemie, nate, plasma-bugs-null
Priority:	NOR
Version First Reported In:	5.22.4
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	Note the choppiness of the letters (Color bands caused by screen, not bug) Fixed (after applying fix mentioned in initial comments)

Description kderemie 2021-08-24 05:41:53 UTC

SUMMARY

Assuming a monitor setup like this:

Primary: 1440p
Secondary: 1080p

If the secondary is disabled and the primary is set to 1440p, then when you enable the second display, the resolution seems to be correctly set to the highest common denominator (1080p) - but the displayed image is visually defective.


STEPS TO REPRODUCE
1. Start with 1440p monitor as primary and 1080p as secondary
2. Ensure you're running 1440p and the secondary monitor is disabled
3. Now enable the secondary monitor using Win+P/Meta+P

OBSERVED RESULT

KDE settings reflects 1080p, but visual issues affect text legibility and edge smoothness.


EXPECTED RESULT

Clear, crisp image.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 21.04
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.85.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION

Screen scaling set to 100% on both displays. Not forcing font DPI setting.

Comment 1 kderemie 2021-08-24 05:43:03 UTC

Issue can be resolved by:

1. Going to display configuration
2. Setting a lower resolution supported on both monitors
3. Selecting 1080p again

Comment 2 kderemie 2021-08-24 05:45:05 UTC

May require being in mirror mode.

Comment 3 kderemie 2021-08-24 05:55:16 UTC

Created attachment 140994 [details]
Note the choppiness of the letters (Color bands caused by screen, not bug)

Comment 4 kderemie 2021-08-24 05:55:56 UTC

Created attachment 140995 [details]
Fixed (after applying fix mentioned in initial comments)

Comment 5 kderemie 2021-08-24 05:58:59 UTC

Nvidia GPU/Xorg, in case it matters.

Comment 6 kderemie 2022-01-19 00:22:56 UTC

Ended up being due to Nvidia defaulting to `60hz (3) (Interlace)`