BrightWheel

BrightWheel is a tray-only Windows application for controlling external monitor brightness over DDC/CI. It talks directly to the Windows monitor configuration API in dxva2.dll and does not depend on ASUS DisplayWidget or its service.

• hover the tray icon and turn the mouse wheel to change primary-monitor brightness; continuous scrolling accelerates dynamically from precise 2% steps up to 10% per notch;
• moving the pointer away from the tray icon cancels wheel input that has not reached the monitor yet, so a long burst does not keep running in the background;
• double-click the tray icon to toggle HDR on the primary monitor;
• right-click to toggle Start with Windows or exit;
• startup is enabled automatically on the first run and can then be disabled from that menu;
• only one instance can run at a time;
• the MSVC runtime is linked statically, so the release executable only uses DLLs included with Windows.

The package also includes bright.exe, an optional command-line companion for diagnostics, scripts, and direct brightness or HDR control.

brightwheel.exe is self-contained and does not ship an ASUS library. The brightness control works with external monitors that expose MCCS VCP 0x10 through Windows DDC/CI; DDC/CI must be enabled in the monitor's on-screen menu. HDR toggling additionally requires a Windows version and primary monitor that support the advanced-color display configuration API.

ASUS XG49V findings

The locally installed ASUS DisplayWidget 3.4.0.041 from Portrait Displays imports these Windows APIs directly from dxva2.dll:

• GetPhysicalMonitorsFromHMONITOR
• GetVCPFeatureAndVCPFeatureReply
• SetVCPFeature
• DestroyPhysicalMonitors

Its UI binds brightness to ddc.vcp16. Decimal 16 is MCCS VCP code 0x10 (luminance/brightness); the control range is 0..100. Contrast is exposed as ddc.vcp18, which maps to VCP 0x12.

The monitor's own capabilities reply identifies it as LCDXG49V, declares MCCS 2.2, and includes VCP 10 and 12. Windows uses the standard Microsoft monitor.inf; there is no ASUS monitor driver in this path.

The app also has a LocalSystem service and named pipes for privileged helper operations, but the brightness path does not require them. Direct VCP read and write both work on the connected ASUS XG49V (DISPLAY\AUS49A1) while DisplayWidget is running.

DDC/CI is a relatively slow serial protocol. The implementation waits briefly after writes and retries transient failures, which also reduces collisions with DisplayWidget's background polling.

Build

Download brightwheel.exe from the latest GitHub Release to run the tray app without installing Rust. The release ZIP also includes the optional CLI.

Install directly from crates.io on Windows:

cargo install brightwheel --locked

Build from a Windows shell:

cargo build --release

Building the tray executable requires the Windows SDK resource compiler (rc.exe) so Cargo can embed assets\brightwheel.ico. The resulting executable loads the tray icon from its own resources; the image files are not needed at runtime.

The repository can live on the WSL filesystem and be built by invoking cargo.exe from WSL. Incremental compilation is disabled for development and test profiles because Windows file locking is not supported for incremental caches accessed through \\wsl.localhost.

The executables are target\release\bright.exe and target\release\brightwheel.exe.

Development

The source is organized by responsibility:

• src/ddc owns physical monitor discovery, DDC/CI retries, and handle cleanup;
• src/autostart.rs and src/hdr.rs wrap their respective Windows APIs;
• src/cli.rs contains the typed command parser and CLI execution;
• src/tray separates gesture policy, Win32 lifecycle, tray presentation, and small resource-owning platform wrappers.

Run the same checks used by CI from a Windows shell. The formatting, Clippy, test, and package commands can also be run by invoking cargo.exe from WSL:

cargo fmt --all -- --check
cargo clippy --all-targets --locked -- -D warnings
cargo test --all-targets --locked
cargo doc --no-deps --locked
cargo publish --dry-run --locked

When running cargo doc through WSL, set CARGO_TARGET_DIR to a Windows-local directory. Rustdoc cannot create its lock file under a \\wsl.localhost target directory; CI and native Windows checkouts are unaffected.

The test suite covers hardware-independent behavior. DDC/CI and HDR integration still require a compatible physical monitor for manual verification.

Release

Pushing a vX.Y.Z tag whose version matches Cargo.toml runs the release workflow. It validates the project, builds both Windows executables, creates a ZIP and SHA-256 checksums, uploads them to a GitHub Release, and publishes the same version to crates.io.

Commands

bright list
bright get [MONITOR]
bright set PERCENT [MONITOR]
bright change DELTA [MONITOR]
bright capabilities [MONITOR]
bright hdr
bright hdr-toggle

Examples:

bright.exe get
bright.exe set 65
bright.exe change -5

get, set, and change print only the resulting percentage, which makes the binary easy to call from a taskbar widget, AutoHotkey, PowerToys, or a tray UI.

API references

• GetVCPFeatureAndVCPFeatureReply
• SetVCPFeature
• GetPhysicalMonitorsFromHMONITOR