https://bugs.kde.org/show_bug.cgi?id=517279
Bug ID: 517279
Summary: Setting QT_IM_MODULE=fcitx in a KDE Wayland session
causes distorted (stretched) candidate windows and
application freezes in Qt programs, which is resolved
by unsetting the variable and using the native Wayland
text-input protocol.
Classification: Applications
Product: systemsettings
Version First 6.6.2
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 190471
--> https://bugs.kde.org/attachment.cgi?id=190471&action=edit
fcitx freezes when typing Chineses
SUMMARY
In a KDE Plasma Wayland session, using Fcitx5 with Qt-based applications (such
as Kate) causes severe UI rendering issues and application freezes. The input
candidate window appears vertically stretched (distorted), and the application
often becomes unresponsive during text input. This issue is specifically
triggered when the QT_IM_MODULE environment variable is set to fcitx. Unsetting
this variable and relying on the native Wayland text-input-v3 protocol (via
Virtual Keyboard settings) resolves the issue, suggesting a conflict between
the legacy IM module and the modern Wayland text input implementation.
STEPS TO REPRODUCE
Start a KDE Plasma Wayland session.
Set environment variables QT_IM_MODULE=fcitx and GTK_IM_MODULE=fcitx (e.g., in
/etc/environment or via PAM).
Open any KDE native application (e.g., Kate) and attempt to type Chinese
characters using Fcitx5.
Observe the candidate window shape and try to interact with the application.
OBSERVED RESULT
The Fcitx5 candidate window is rendered as a very long, thin, and stretched
rectangle that does not match the system DPI/scaling.
The application (Kate) frequently freezes or becomes "locked" while the input
method is active, requiring a force kill or switching focus multiple times to
recover.
EXPECTED RESULT
The candidate window should be rendered with correct proportions and scaling.
The application should remain responsive regardless of whether a legacy IM
module is specified or the native Wayland protocol is used.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux (Kernel 6.12.74-1-lts)
KDE Plasma Version: (Please run kinfo and paste here)
KDE Frameworks Version: (Please run kinfo and paste here)
Qt Version: 6.x (Detected via fcitx5-diagnose as using fcitx5-qt6 module)
ADDITIONAL INFORMATION
Fcitx version: 5.1.17
Environment: Wayland session with fcitx5-qt and fcitx5-gtk modules installed.
Workaround: Manually launching applications with QT_IM_MODULE= (empty) and
using the "Virtual Keyboard -> Fcitx 5" setting in System Settings fixes both
the stretching and the freezing.
The issue seems to involve a deadlock or synchronization failure between the
Wayland compositor (KWin) and the Qt IM module during cursor position updates
or scaling calculations.
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