Have you added the udev rules that are in the readme?

Yes, and they seem to have worked:

$ ls -lah /sys/class/backlight/intel_backlight/brightness
.rw-rw-r-- root video 4.0 KB Tue May  9 19:34:29 2023 /sys/class/backlight/intel_backlight/brightness
$ groups
wireshark seat libvirt docker video kvm sudo russell

I've played around with the brightness code a little bit and this patch seems to work (minus some bounds checks):

diff --git a/src/utils.rs b/src/utils.rs
index c8e2198..7dbd7c0 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -8,7 +8,7 @@ use std::{
 	sync::Mutex,
 };
 
-use blight::{change_bl, err::BlibError, Change, Device, Direction};
+use blight::{err::BlibError, Delay, Device, Direction};
 use pulse::volume::Volume;
 use pulsectl::controllers::{types::DeviceInfo, DeviceControl, SinkController, SourceController};
 
@@ -265,25 +265,20 @@ pub fn change_brightness(
 		.unwrap_or(String::new())
 		.parse::<u8>()
 		.unwrap_or(BRIGHTNESS_CHANGE_DELTA) as u16;
-	let direction = match change_type {
-		BrightnessChangeType::Raise => Direction::Inc,
-		BrightnessChangeType::Lower => {
-			let device = Device::new(None)?;
-			let change = device.calculate_change(brightness_delta, Direction::Dec) as f64;
-			let max = device.max() as f64;
-			// Limits the lowest brightness to 5%
-			if change / max < (brightness_delta as f64) * 0.01 {
-				return Ok(Some(device));
-			}
-			Direction::Dec
-		}
+	let mut device = Device::new(None)?;
+	let change = match change_type {
+		BrightnessChangeType::Raise => device.calculate_change(brightness_delta, Direction::Inc),
+		BrightnessChangeType::Lower => device.calculate_change(brightness_delta, Direction::Dec),
 	};
-	match change_bl(brightness_delta, Change::Regular, direction, None) {
+	match device.sweep_write(change, Delay::default()) {
 		Err(e) => {
 			eprintln!("Brightness Error: {}", e);
 			Err(e)
 		}
-		_ => Ok(Some(Device::new(None)?)),
+		_ => {
+			device.reload();
+			Ok(Some(device))
+		}
 	}
 }
 

A few things that stood out that are kind of weird about the existing code is the recreation of the Device as it is only used to be passed to the window.changed_brightness function where the Device is used to get the current and max value. It might be a better abstraction to just pass in the values directly rather than relying on the implementation of the device to return those values. The other change is to use the sweep_write method for smoother transitions.

Anyways, thanks for creating this project it's really nice!

Sorry for the massive delay, this got lost in my emails...

Can you open a PR with these changes? Makes it easier for me to keep track of stuff :)

Having the same issue on NixOS. Volume control works great, but exec swayosd --brightness raise shows the brightness bar at maximum, and exec swayosd --brightness lower doesn't show anything and doesn't lower the brightness.
brightnessctl does work on this machine btw.

Same issue here on nixos on an intel based machine. Changing it manually with an echo command or brightnessctl works correctly though.

Would it be possible to add some debug logs in the program?

I'll try to get this issue fixed within a couple of days. If I forget, please don't be afraid to ping me :)

@augustebaum @aacebedo have you installed the udev rules properly? If so, please provide the output of: cat /sys/class/backlight/*/brightness and cat /sys/class/backlight/*/max_brightness

The udev rules were correctly set. I installed the latest version and it seems to work. Will check if it continues to work.

@ErikReider Hmm did you forget? :3

For anyone having this problem on nixos adding the user to video group and manually setting the group and permissions of /sys/class/backlight/*/brightness fixed it for me.
I manually ran sudo chgrp video /sys/class/backlight/intel_backlight/brightness and sudo chmod g+w /sys/class/backlight/intel_backlight/brightness and put the following in the configuration.nix

  users.users.${username} = {
    isNormalUser = true;
    description = name;
    extraGroups = [ "networkmanager" "wheel" "video"];
  };

For anyone having this problem on nixos adding the user to video group and manually setting the group and permissions of /sys/class/backlight/*/brightness fixed it for me. I manually ran sudo chgrp video /sys/class/backlight/intel_backlight/brightness and sudo chmod g+w /sys/class/backlight/intel_backlight/brightness and put the following in the configuration.nix

  users.users.${username} = {
    isNormalUser = true;
    description = name;
    extraGroups = [ "networkmanager" "wheel" "video"];
  };

I find that NixOS will change file permission everytime we run nix rebuild, so I add these configuration to automatically change the file permission:

  system.activationScripts = {
    # swayosd cannot set brightness issue on NixOS
    # see https://github.com/ErikReider/SwayOSD/issues/12#issuecomment-1950581102
    fix-brightness-file-permission.text = ''
chgrp video /sys/class/backlight/intel_backlight/brightness
chmod g+w /sys/class/backlight/intel_backlight/brightness
'';
  };

I discovered setting the udev rules provided by swayosd with adding this to my configuration.nix

services.udev.packages = [ pkgs.swayosd ];

I think this fixes the issue of reverting permissions after rebuild :)