feat: add wayland ddc/ci backend for external monitors

README.md

@@ -11,28 +11,29 @@ greenfix is released under the MIT License.
 greenfix is designed for Linux desktop sessions where `xrandr` can control the active display output.
 
 - X11: best supported.
-- Wayland: may not work because most Wayland sessions do not allow `xrandr` to change display settings.
+- Wayland (COSMIC and others): supported for **external monitors that speak DDC/CI**. greenfix shells out to `ddcutil` and adjusts VCP brightness (`0x10`) plus per-channel RGB gain (`0x16/0x18/0x1A`). Laptop panels are not supported under Wayland because they don't expose DDC/CI and cosmic-comp does not yet expose `wlr-gamma-control-unstable-v1` (tracking [pop-os/cosmic-comp#2059](https://github.com/pop-os/cosmic-comp/issues/2059)).
 - Root access: not required.
 
-If `XDG_SESSION_TYPE` is `wayland`, the app warns that display changes may not work but still lets you try.
+If `XDG_SESSION_TYPE` is `wayland`, greenfix uses the DDC/CI backend automatically. If no DDC/CI-capable monitors are detected, the UI says so and explains the limitation.
 
 ## Requirements
 
 - Python 3.10 or newer.
 - `xrandr`, usually provided by `x11-xserver-utils`, `xorg-xrandr`, or a similar package.
 - GTK 3 and PyGObject for the desktop UI.
+- `ddcutil` (only on Wayland; not needed for X11). Your user must be in the `i2c` group for `ddcutil` to access `/dev/i2c-*` without sudo.
 
 Common dependency packages:
 
 ```bash
 # Debian, Ubuntu, Pop!_OS
-sudo apt install python3-gi gir1.2-gtk-3.0 x11-xserver-utils
+sudo apt install python3-gi gir1.2-gtk-3.0 x11-xserver-utils ddcutil
 
 # Fedora
-sudo dnf install python3-gobject gtk3 xrandr
+sudo dnf install python3-gobject gtk3 xrandr ddcutil
 
 # Arch Linux
-sudo pacman -S python-gobject gtk3 xorg-xrandr
+sudo pacman -S python-gobject gtk3 xorg-xrandr ddcutil
 ```
 
 The greenfix installer does not run a system package manager. If Python or `xrandr` is missing, it prints suggestions and exits. If GTK/PyGObject is missing, it prints suggestions and still installs the CLI launcher so non-UI commands can work.