xfce4-ddc-brightness-slider

GTK3 system tray applet for XFCE4 that controls external monitor brightness via DDC/CI protocol.

Features

• Tray icon left click opens a brightness popup right next to the panel
• Slider with 150 ms debounce, smooth dragging without spamming ddccontrol
• Quick presets 1 %, 10 %, 25 %, 50 %, 75 %, 100 % buttons below the slider
• Auto-detection of the monitor I2C bus during installation
• Standalone mode floating window as an alternative to the tray
• Lightweight single Python file, no build step, no pip packages

Requirements

• Linux with an external monitor that supports DDC/CI
• XFCE4 (or any DE with a system tray / status notifier area)
• Python 3.8+
• GTK 3

Installation

Via script

git clone https://github.com/krsnv/xfce4-ddc-brightness-slider.git
cd xfce4-ddc-brightness-slider
chmod +x install.sh
./install.sh

The installer will:

1. Install system packages (ddccontrol, python3-gi, gir1.2-gtk-3.0)
2. Create the i2c group and udev rule for non-root access to /dev/i2c-*
3. Add your user to the i2c group
4. Copy the script to /usr/local/bin/
5. Set up autostart for your XFCE session
6. Probe all I2C buses to find your monitor

Manual installation

Ubuntu/Debian

sudo apt install ddccontrol python3-gi gir1.2-gtk-3.0
sudo modprobe i2c-dev
echo "i2c-dev" | sudo tee /etc/modules-load.d/i2c-dev.conf

sudo groupadd -f i2c
sudo usermod -aG i2c $USER
echo 'KERNEL=="i2c-[0-9]*", GROUP="i2c", MODE="0660"' | sudo tee /etc/udev/rules.d/99-i2c.rules
sudo udevadm control --reload-rules && sudo udevadm trigger

sudo cp ddc-brightness-slider.py /usr/local/bin/
sudo chmod +x /usr/local/bin/ddc-brightness-slider.py

Arch Linux

sudo pacman -S ddccontrol python-gobject gtk3

sudo modprobe i2c-dev
echo "i2c-dev" | sudo tee /etc/modules-load.d/i2c-dev.conf

sudo groupadd -f i2c
sudo usermod -aG i2c $USER
echo 'KERNEL=="i2c-[0-9]*", GROUP="i2c", MODE="0660"' | sudo tee /etc/udev/rules.d/99-i2c.rules
sudo udevadm control --reload-rules
sudo udevadm trigger

sudo cp ddc-brightness-slider.py /usr/local/bin/ddc-brightness-slider.py
sudo chmod +x /usr/local/bin/ddc-brightness-slider.py

Troubleshooting

"Permission denied" on /dev/i2c-*

# Make sure the udev rule exists
cat /etc/udev/rules.d/99-i2c.rules
# Should contain: KERNEL=="i2c-[0-9]*", GROUP="i2c", MODE="0660"

# Make sure you're in the i2c group
groups | grep i2c

# If not, add yourself and relog
sudo usermod -aG i2c $USER

ddccontrol can't find the monitor

# Make sure i2c-dev is loaded
sudo modprobe i2c-dev

# Scan for monitors
sudo ddccontrol -p

# Try each bus manually
for dev in /dev/i2c-*; do
    echo "--- $dev ---"
    ddccontrol -r 0x10 "dev:$dev" 2>/dev/null | grep -E '\+/|current'
done

Uninstall

sudo rm /usr/local/bin/ddc-brightness-slider.py
rm ~/.config/autostart/ddc-brightness-slider.desktop
rm ~/.local/share/applications/ddc-brightness-slider.desktop

Contributing

Contributions are welcome. If you would like to improve the plugin, please fork the repository, create a separate branch for your changes, and submit a pull request with a clear description of what was modified and why.

For bug reports, feature requests, or any other problems you notice, please open an Issue in this repository. Describe the problem in detail, including your system configuration, steps to reproduce (if applicable), and any relevant logs or screenshots.

All detected problems should be reported as Issues so they can be tracked and addressed properly.