KWin Horizontal Sliding Notifications (Plasma 6)

This KWin effect provides a tactile, spring-y horizontal slide for Plasma notifications, replacing the default fade animations. Originally designed for KDE Neon, this version has been updated with a generic build system to support various Plasma 6 distributions.

Confirmed as working on Plasma 6.6.1

• This effect has been updated for KDE Plasma 6.6.
• API: Uses the new KWin::Region signature.
• Path: Plugins must now be installed to /usr/lib/qt6/plugins/kwin/effects/.
• Sound: Uses pw-play with the Ocean sound theme (.oga).

Installation for Plasma 6 (Note: tested on CachyOS):

mkdir build && cd build
cmake ..
make
sudo install -m 755 kwin_final_sliding.so /usr/lib/qt6/plugins/kwin/effects/
sudo ln -s /usr/lib/qt6/plugins/kwin/effects/kwin_final_sliding.so /usr/lib/qt6/plugins/kwin/effects/plugins/kwin_final_sliding.so

Key Features

• Horizontal Only: Strict lock on the Y and Z axes to prevent diagonal drifting.
• Tactile Entrance: Uses an OutBack easing curve for a physical “snap” feel.
• Stealth Exit: A manual timer-based exit that “cuts the feed” before KWin unmaps the window, eliminating final-frame stutter.
• Notification Sound: Automatically triggers a notification sound using pw-play.
• Generic Compatibility: Uses CMake discovery to find KWin headers regardless of whether the distro uses /usr/include/kwin or /usr/include/KWin.

Prerequisites

To build this plugin, you need the C++ development environment and KWin/KF6 headers.

KDE Neon / Ubuntu / Kubuntu

sudo apt install g++ cmake extra-cmake-modules libkwin-dev \
     libkf6config-dev libkf6configwidgets-dev libkf6coreaddons-dev \
     libkf6windowsystem-dev qt6-base-dev

Fedora

sudo dnf install gcc-c++ cmake extra-cmake-modules kwin-devel \
     kf6-kconfig-devel kf6-kconfigwidgets-devel kf6-kcoreaddons-devel \
     kf6-kwindowsystem-devel qt6-qtbase-devel

Arch Linux

sudo pacman -S base-devel cmake extra-cmake-modules kwin \
     kconfig kconfigwidgets kcoreaddons kwindowsystem qt6-base

Notification Sound

The effect is hardcoded to play a sound via PipeWire on window entry:

• Command: /usr/bin/pw-play
• Target: /usr/share/sounds/oxygen/stereo/message-new-instant.ogg

Note: If the sound file or pw-play is missing, the plugin will remain silent and continue to function normally without crashing.

How to Install

1. Build the Plugin

The generic CMakeLists.txt will automatically detect your system's library paths.

mkdir build && cd build
cmake ..
make

2. Install

This will install the plugin to the appropriate KDE Qt6 plugin directory:

sudo make install

3. Activate & Reload

Enable the plugin and tell KWin to reload its effects without restarting your session:

# Enable the plugin
kwriteconfig6 --file kwinrc --group Plugins --key kwin_final_slidingEnabled true

# Reload KWin effects
qdbus6 org.kde.KWin /Effects org.kde.KWin.Effects.loadDefaultEffects

Troubleshooting

KWin 6 headers are not considered a stable API. If the build fails:

• Missing Headers: Ensure libkwin-dev (or your distro's equivalent) is installed. The CMake script looks for effect/effect.h.
• Library Mismatch: The script looks for libkwin.so.6. If you are on an older or experimental system, verify your KWin library version in /usr/lib/.
• Logs: Check journalctl -f while reloading effects to see if KWin reports any "Plugin could not be loaded" errors.