https://bugs.kde.org/show_bug.cgi?id=507268
Bug ID: 507268
Summary: Strong lags with bitmap fonts and long strings and no
word wrap
Classification: Applications
Product: kate
Version First 25.04.3
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: minor
Priority: NOR
Component: kwrite
Assignee: kwrite-bugs-n...@kde.org
Reporter: m...@mvv.su
Target Milestone: ---
SUMMARY
Hello.
I've noted that, using Kwrite, (and same with Kate), in some rare condition:
* Using bitmap fonts,
* And have long strings (> 2k chars each in my case),
* And with turned off dynamic word wrap. (View -> Word wrap),
i have strong lags when navigating/scrolling large text file. I've shared it
here.
But, if i `gunzip` the `.pcf.gz` fonts, to make them `.pcf`, (and `fc-cache
-fv`), the lags are disappear. I've tested with `ibm-fonts` like 8x8 BIOS font,
and with Terminus.
I have Archlinux and XFCE; i also confirm this issue on other (similar)
machine.
I can live with it, as i found this simple workaround with `gunzip`, so
severity is low.
STEPS TO REPRODUCE
1. Have fresh Archlinux + XFCE.
2. Install `kwrite` and `kate` using `pacman`.
3. Install fonts: `pacman -S terminus-font`; `yay -S ibm-fonts`.
4. Open attached text file using `kwrite`.
5. Settings - Configure Kwrite - Editor font - `Ibm Bios 8x8 wide`.
6. View - Word wrap - turn off Dynamic word wrap.
7. Scroll document (PgUp/PgDn), see lags.
8. Close Kwrite.
9. `cd /usr/share/fonts/misc/` ; `gunzip i*` (use with care, do not run on
production machine). `.pcf.gz` fonts should become `.pcf`.
10. `fc-cache -fv`
11. Repeat steps above and see there is no lags any more.
OBSERVED RESULT
Huge lags when scrolling on normal system (font in its normal `.pcf.gz` state)
EXPECTED RESULT
No text navigating lags, like using `gunzip` workaround.
SOFTWARE/OS VERSIONS
Windows: no
macOS: no
Linux/KDE Plasma: Archlinux + XFCE, but no KDE Plasma yet.
KDE Plasma Version: no
KDE Frameworks Version: no
Qt Version:
`qtdiag6`
Qt 6.9.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC
15.1.1 20250425) on "xcb"
OS: Arch Linux [linux version 6.15.7-arch1-1]
Architecture: x86_64; features: SSE2 SSE3 SSSE3 SSE4.1 SSE4.2 AVX AVX2 RDRAND
RDSEED AES
Environment:
QT_QPA_PLATFORMTHEME="qt5ct"
Features: QT_NO_EXCEPTIONS
ADDITIONAL INFORMATION
1. Only .bdf/.pcf(.gz) fonts are tested, `.otb` are not tested.
2. There is no any display issues with all these fonts (wrong
letters/size/position...), only lags.
Thanks to dev teams for valuable and useful work and support.
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