Dimmer smoothly transitions your screen from one brightness to another. Very simple, and only tested with Wayland and recent Linux kernels.

# Show usage information
dimmer --help

# Dim the screen to zero brightness over 5 seconds
dimmer

# Dim (or brighten) the screen to 30%, first saving the current brightness to a statefile
dimmer --save --duration 5s 30%

# Restore the screen from a previously saved brightness, using 2 seconds
dimmer --restore --duration 2s

Many people like to automatically turnoff & lock their screen after a period of idleness and it would sure be nice if we could smoothly dim the screen before turning it off (and smoothly restore the brightness later). When we interact with the system during the dimming process, we'd like the dimming process to stop and the brightness to quickly be restored.

Swayidle offers no possibilities for signals to be send to a (dimming) process that is already running, so the reaction to the new user input would have to come from a new process. However, the swayidle(1) man-page recommends for security purposes to use the -w flag to wait for triggered commands to finish when used in combination with a screenlock, which would make it impossible for us to interrupt the screen dimming process on user input.

For this reason, I recommend running one swayidle process with the -w flag to trigger the locking command, and another swayidle process without the -w flag to trigger the dimmer commands.

exec swayidle -w \
  timeout 620 'swaymsg "output * dpms off"' \
  timeout 625 'swaylock -f' \
  timeout 630 'systemctl suspend'

exec swayidle \
  timeout 600 'dimmer --save' \
  resume 'pkill dimmer; dimmer --restore --duration 1s'

Setting the backlight works by writing to a special file in /sys (exposed by the kernel for this purpose), which on many distro's requires the user to be a member of a group, often video. If you receive a Permission denied error, chances are your user needs additional privileges to be able to write to the file.

Check ls -l /sys/class/backlight/*/brightness for the permissions on the backlight file and the group you can add your user to.

nix run github:koenw/dimmer

cargo install dimmer