Bug 509828

Summary: Font preview cannot show characters outside the Basic Multilingual Plane (BMP) correctly
Product: [Applications] systemsettings Reporter: Huanyu Liu <1293660441>
Component: kcm_fontinstAssignee: Plasma Bugs List <plasma-bugs-null>
Status: CONFIRMED ---    
Severity: normal CC: kdedev, nate
Priority: NOR    
Version First Reported In: 6.4.5   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description Huanyu Liu 2025-09-23 14:33:01 UTC 
SUMMARY
Font preview cannot show characters outside the Basic Multilingual Plane (BMP) correctly.

STEPS TO REPRODUCE
Take "二𫫇英" (U+4E8C U+2BAC7 U+82F1, meaning "dioxin" in Chinese) as an example. Make sure you have installed a font that supports the second character "𫫇" (U+2BAC7), such as Noto Sans/Serif [CJK] SC or Unifont.
1. Launch System Settings
2. Go to Text & Fonts → Font Management, and select a font mentioned above
3. Right click on the font preview, and select "Change Preview Text..."
4. Paste the text "二𫫇英" and press "OK"

OBSERVED RESULT
The preview becomes "二??英", where "?" indicates the notdef glyph.


EXPECTED RESULT
The text "二𫫇英" should be previewed correctly.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.16.8-arch2-1 (64-bit)
Graphics Platform: Wayland

ADDITIONAL INFORMATION
Since a single character becomes two notdef glyphs, I suspect it is a problem related to UTF-16 handling failure.
Comment 1 TraceyC 2025-10-09 17:43:00 UTC 
I can reproduce this on git-master using the Noto Sans CJK font