Bug 513783

Summary: With fractional scale factor, 1px gap between window and its outline when it's moved between screens
Product: [Plasma] Breeze Reporter: aronkvh
Component: window decorationAssignee: Plasma Bugs List <plasma-bugs-null>
Status: REPORTED ---    
Severity: normal CC: akselmo, kwin-bugs-null, nate, uhhadd
Priority: NOR Keywords: multiscreen
Version First Reported In: 6.5.4   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: outline gap
outline gap full height

Description aronkvh 2025-12-24 14:46:29 UTC 
Created attachment 187942 [details]
outline gap

SUMMARY
If I move any app from the secondary screen to the primary, the outline gets a one pixel gap.
The secondary screen has fractional scaling, the primary doesn't.

Output: 1 eDP-1 efd88d26-5b49-422a-b003-6a751b915f08
        enabled
        connected
        priority 2
        Panel
        replication source:0
        Modes:  1:2560x1600@165.00*!  2:2560x1600@60.00 
        Geometry: 1920,13 1707x1067
        Scale: 1.5
        Rotation: 1
        Overscan: 0
        Color profile source: sRGB
        Color power preference: prefer efficiency and performance
        Brightness control: supported, set to 55% and dimming to 100%
        Color resolution: unknown
        Allow EDR: always
        Sharpness control: unsupported
Output: 2 HDMI-A-1 094af994-325a-472f-8c9f-2b8ef9b9812a
        enabled
        connected
        priority 1
        HDMI
        replication source:0
        Modes:  3:1920x1080@60.00*!  4:1920x1080@60.00  5:1920x1080@59.94  6:1920x1080@50.00  7:1600x1200@60.00  8:1680x1050@59.95  9:1280x1024@75.03  10:1280x1024@60.02  11:1440x900@59.89  12:1280x720@59.94  13:1280x720@50.00  14:1024x768@75.03  15:1024x768@60.00  16:800x600@75.00  17:800x600@60.32  18:800x600@56.25  19:720x576@50.00  20:720x480@59.94  21:640x480@75.00  22:640x480@72.81  23:640x480@59.94  24:640x480@59.93 
        Geometry: 0,0 1920x1080
        Scale: 1
        Rotation: 1
        Overscan: 0
        HDR: incapable
        Color profile source: EDID
        Color power preference: prefer efficiency and performance
        Brightness control: supported, set to 100% and dimming to 100%
        DDC/CI: allowed
        Color resolution: unknown

STEPS TO REPRODUCE
1. Move a window to the primary screen
2. Move it to the secondary screen

OBSERVED RESULT
On the right and bottom edges, there is a 1px transparent area between the window and the outline.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 43
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
Kernel Version: 6.17.12-300.fc43.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 260 w/ Radeon 780M Graphics
Graphics Processor 1: NVIDIA GeForce RTX 5060 Laptop GPU
Graphics Processor 2: AMD Radeon 780M Graphics
Comment 1 aronkvh 2025-12-24 14:46:48 UTC 
Created attachment 187943 [details]
outline gap full height
Comment 2 Nate Graham 2026-01-08 18:49:46 UTC 
Does it still happen with a scale factor of 100% or 200%?
Comment 3 aronkvh 2026-01-08 19:52:27 UTC 
(In reply to Nate Graham from comment #2)
> Does it still happen with a scale factor of 100% or 200%?

No, only fractional scales.
Weirdly, if the scale factor is under 150%, the gap will be on the display with the 100<scale<150. (in my setup output 1)
If the scale factor is higher than 150%, the gap will show up on the display scaled to 100% (Output 2)