wluma

A tool for Wayland compositors to automatically adjust screen brightness based on the screen contents and amount of ambient light around you.

Supported screen capture protocols

With default config, wluma will automatically detect which protocols are supported, and pick the most appropriate one. See "Configuration" section below for more information and how to force a specific protocol.

The list of supported protocols:

• ext-image-capture-source-v1 - the newest protocol that potentially is (or will be) supported by any modern Wayland desktop environment.
  • At the time of writing, it's not supported by any compositor yet.
  • requires ext-image-capture-source-v1 and linux-dmabuf-v1 protocol to be supported as well.
• wlr-screencopy-unstable-v1 - supported by any wlroots-based compositors (e.g. sway), as well as Hyprland.
  • requires linux-dmabuf-v1 protocol to be supported as well.
• wlr-export-dmabuf-unstable-v1 - supported by any wlroots-based compositors (e.g. sway).

Idea

The app will automatically brighten the screen when you are looking at a dark window (such as a fullscreen terminal) and darken the screen when you are looking at a bright window (such as web browser). The algorithm takes into consideration the amount of ambient light around you, so the same window can be brighter during the day than during the night.

With permission of Lumen's author (the project that inspired me to create this app), I'm reusing a demo GIF:

Usage

Simply launch wluma and continue adjusting your screen brightness as you usually do - the app will learn your preferences.

wluma will not do anything on the first launch! You have to adjust the brightness by hand a few times, in different environment and/or with different screen contents, that way wluma will learn your preferences and only then it will begin to automatically change your screen brightness for you.

Performance

The app has minimal impact on system resources and battery life even though it is able to monitor screen contents several times a second. This is achieved by using Wayland protocols to get access to the screen contents and doing computations entirely on GPU using Vulkan API.

Installation

Use one of the available packages and methods below:

• Alpine Linux: wluma
• Arch Linux: wluma or wluma-git
• NixOS: wluma
• Build the app yourself using the instructions below and copy the resulting binary somewhere in your $PATH.
  • optionally, grab the wluma.service if you want to run it as a systemd-service - it can be placed e.g. in ~/.config/systemd/user/.
  • you might need 90-wluma-backlight.rules too, if you want to give wluma direct driver access for the fastest performance (see "Permissions" section below) - it can be placed e.g. in /etc/udev/rules.d/.

Build

If you want to build the app yourself, make sure you use latest stable Rust, otherwise you might get compilation errors! Using rustup is perhaps the easiest. Ubuntu needs the following dependencies: sudo apt-get -y install v4l-utils libv4l-dev libudev-dev libvulkan-dev libdbus-1-dev.

Then simply run cargo build --locked --release and the binary will be placed into ./target/release/wluma.

Permissions

In order to access backlight devices, wluma must either:

• have direct driver access: install the supplied 90-wluma-backlight.rules udev rule, add your user to the video group and reboot (fastest, most likely a requirement for smooth transitions)
• run on a system that uses elogind or systemd-logind (they provide a safe interface for unprivileged users to control device's brightness through dbus, no configuration necessary)
• run as root (not recommended)

Configuration

The config.toml in repository represents default config values. To change them, copy the file into $XDG_CONFIG_HOME/wluma/config.toml and adjust as desired.

ALS

Choose whether to use a real IIO-based ambient light sensor ([als.iio]), a webcam-based simulation ([als.webcam]), a time-based simulation ([als.time]) or disable it altogether ([als.none]).

Each of them contains a thresholds field, which comes with good default values. It is there to convert generally exponential lux values into a linear scale to improve the prediction algorithm in wluma. Keys are the raw values from ambient light sensor (maximal value depends on the implementation), values are arbitrary "profiles". wluma will predict the best screen brightness according to the data learned within the same ALS profile.

Displays

Multiple outputs are supported, using backlight (common for internal laptop screens) and ddcutil (for external screens). DDC is known to often be problematic, always consider trying out ddcci-driver-linux first if you can.

Each output is identified by compositor using model, manufacturer and serial number (e.g.eDP-1 'Sharp Corporation 0x14A8 0x00000000' (eDP-1).

The name field in the output config will be matched as a substring, so you are free to put simply eDP-1, or a serial number (if you have two identical external screens). It is your responsibility to make sure that the values you use match uniquely to one output only.

Tip: run wluma with RUST_LOG=debug to see how your outputs are being identified, so that you can choose an appropriate name configuration value.

The capturer field will determine how screen contents will be captured. Currently supported values are wayland (works only on Wayland compositors that support protocols listed in the top) and none (ignores screen contents and predicts brightness only based on ALS). The value wayland will automatically choose the most appropriate protocol, but if you want to force a specific one, you can also use ext-image-capture-source-v1, wlr-screencopy-unstable-v1 or wlr-export-dmabuf-unstable-v1 as the value.

Tip: run wluma with RUST_LOG=debug and capturer="wayland" to see which protocols are supported by your Wayland compositor, and which one wluma chooses to use.

Algorithm

The default algorithm that wluma uses is called adaptive, which is when it learns from you as you continue adjusting brightness manually. It will eventually figure out patterns in how you tend to adjust brightness in dark and lit conditions and depending on what is currently being displayed on the screen, and will beging to do it automatically for you.

If you instead want to preserve control over absolute brightness value, but let wluma only do relative adjustments, there is an alternative algorithm called manual. It can be useful if you feel like wluma is unable to learn the patterns, for example because you don't have a real ambient light sensor, and neither of the alternative ALS inputs are able to capture the real light conditions precisely enough.

Here's how you enable the manual algorithm in the config:

[als.time]
thresholds = { 0 = "night", 8 = "day", 18 = "night" }

[[output.backlight]]
name = "eDP-1"
path = "/sys/class/backlight/intel_backlight"
capturer = "wayland"
[output.backlight.predictor.manual]
thresholds.day = { 0 = 0, 100 = 10 }
thresholds.night = { 0 = 0, 100 = 60 }

In other words, you activate the predictor for a given output using [output.backlight.predictor.manual], and then you define thresholds for each ALS condition using the following syntax:

thresholds.<als threshold name> = {<luma> = <brightness reduction percentage>}

• luma is the "whiteness" of your screen contents, measured in percentage, from 0 to 100.
• Current screen brightness (that you set manually) will be reduced by the corresponding brightness reduction percentage based on what is currently being displayed on the screen.
• als threshold name is the custom name that you define in ALS thresholds. When using [als.none], the als threshold name is none.
• You can define as many entries within each threshold as you want (up to 100, for every single luma value). The algorithm will interpolate between the values you define.

The example config above expresses the following intention:

• During the day, the screen brightness will be reduced upmost by 10% of the value you set - fully black screen does not reduce the brightness at all, fully white screen reduces it by 10%, screen contents with "whiteness" of 70% will reduce the brightness by 7%, etc.
• During the day, the screen brightness will be reduced upmost by 60% of the value you set - using the same logic as above.

Run

To run the app, simply launch wluma or use the provided systemd user service.

Debugging

To enable logging, set environment variable RUST_LOG to one of these values: error, warn, info, debug, trace.

For more complex selectors, see env_logger's documentation.

Validating that wluma is able to see screen contents correctly

This is a useful test to validate that wluma does indeed see the screen contents correctly. This is obviously only applicable if you didn't disable capturer in your config.

1. Stop any running wluma instances
2. Run the latest code from main branch (unless another branch was given to you by the maintainers): RUST_LOG=trace cargo run
3. Open https://deadpixeltest.org/ and start the test.
4. Make sure that the entire screen is covered with a single solid color, nothing else should be visible - not a status bar nor a notification, nothing else.
5. Repeat for each of these colors: black, white, red, green, blue:
   1. Let the color be visible for a few seconds.
   2. Quickly go back to the running wluma and check the luma value reported for that color: Prediction: 252 (lux: none, luma: ---> 14 <---)
6. Compare your values with the following expected results:

   black: 0
   white: 100
   red: 49
   green: 83
   blue: 26
   

If your results do not match, please open an issue and let's investigate!

Known issues (help wanted!)

Help is wanted and much appreciated! If you want to implement some of these, feel free to open an issue and I'll provide more details and try to help you along the way.

• Support for frames with custom DRM modifiers (e.g. multi-planar frames) is currently not implemented. This was implemented in mesa and can finally be added to wluma. Until then, a workaround is to export WLR_DRM_NO_MODIFIERS=1 before launching your wlroots-based compositor.
• Plugging in a screen while wluma is running. Workaround: restart wluma.

Relevant projects

• lumen: project that inspired me to create this app