Bug 499289

Summary: Font Management KCM preview exhibits jagged rendering with Wayland and fractional scaling
Product: [Applications] systemsettings Reporter: Gilles Gagniard <gilles>
Component: kcm_fontsAssignee: Plasma Bugs List <plasma-bugs>
Status: CONFIRMED ---    
Severity: normal CC: greenulito, john.kizer, kdedev, madness742, nate, u0sd2qpny
Priority: NOR    
Version First Reported In: 6.2.5   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
See Also: https://bugs.kde.org/show_bug.cgi?id=502322
https://bugs.kde.org/show_bug.cgi?id=502103
Latest Commit: Version Fixed In:
Sentry Crash Report:
Attachments: Font Management with bad font rendering in preview panel

Description Gilles Gagniard 2025-01-29 19:42:11 UTC 
Created attachment 177800 [details]
Font Management with bad font rendering in preview panel

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SUMMARY


STEPS TO REPRODUCE
1. Use Plasma Wayland session, 150% scale in System Settings > Display & Monitor 
2. Open System Settings > Text & Fonts > Font Management and select any font
3. 

OBSERVED RESULT
The font rendering in the preview panel on the right is atrocious (no antialiasing, hinting broken), while the other fonts in the app render correctly; see attached screenshot.

EXPECTED RESULT
Fonts are rendered correctly with antialiasing and correct hinting.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1

ADDITIONAL INFORMATION
Comment 1 Nate Graham 2025-01-30 17:57:09 UTC 
Can reproduce.
Comment 2 TraceyC 2025-04-07 15:42:26 UTC 
*** Bug 501975 has been marked as a duplicate of this bug. ***
Comment 3 Alex J Green 2025-04-20 11:24:24 UTC 
This issue is not limited to the Font Management KCM — it also affects other software, applications, and browsers. Assuming it's only related to the Font KCM creates a false impression that the problem is minor and can be postponed. In reality, it's a broader and more important issue that deserves timely attention.
Comment 4 Gilles Gagniard 2025-09-02 19:56:32 UTC 
(In reply to Alex J Green from comment #3)
> This issue is not limited to the Font Management KCM — it also affects other
> software, applications, and browsers. Assuming it's only related to the Font
> KCM creates a false impression that the problem is minor and can be
> postponed. In reality, it's a broader and more important issue that deserves
> timely attention.

Indeed, there are several "old" KDE applications (examples: KolourPaint, KPatience) whose rendering seem to be broken as well with similar symptoms. Maybe the issue is not related to font rendering itself, but a more general bitmap scaling issue when fractional scaling is enabled.