How it works

Windows: Raw Input for the HID digitizer usage page 0x0D / touchpad 0x05, parsed with HidP_*, so it keeps working while other windows have focus. A WH_MOUSE_LL hook hides edge clicks and freezes the pointer. SendInput sends keys. Brightness goes through WMI on a background thread. The settings window, tray icon and on-screen display are plain Win32 with per-monitor DPI awareness.
Linux: the touchpad is read from /dev/input/event* (evdev multitouch protocol B). Keys, media keys and the zoom wheel are sent through virtual uinput devices. A tiny local web server serves the settings page.
Shared: the settings, the touchpad geometry and the whole gesture engine are the same code on both systems.

No network access, no telemetry. Margin only reads the touchpad and writes your settings and a small log file.

#Build and test

cargo build --release      # target/release/margin  (margin.exe on Windows)
cargo test                 # unit tests: settings, geometry, shortcuts, the gesture engine, the evdev parser...

Tests that use real hardware or the registry are marked #[ignore] and run on request (Windows):

powershell

cargo test brightness_write -- --ignored --nocapture   # nudges the panel by 1 %, reads it back, restores it
cargo test startup_round_trip -- --ignored             # writes and removes the "start with Windows" value

On Linux, tools/linux-e2e.py runs the real daemon against a fake touchpad created through uinput, performs finger gestures and checks the key events that come out (volume, Alt held through a slide, corner presses, settings reload, custom keys). It needs root and a kernel with uinput, and a desktop would also see the fake touchpad, so use a VM, container or WSL:

cargo build --release && sudo python3 tools/linux-e2e.py target/release/margin

#Code layout

Everything runs on one thread per program (Windows: one message loop; Linux: one poll loop). The gesture logic has no OS calls in it, so it is unit-tested without a touchpad.

Module	Role
`settings.rs`, `geometry.rs`	settings model and JSON; where each edge and corner sits on the pad
`engine.rs`	the gesture state machine; turns touch frames and clicks into effects (pure, tested)
`keys.rs`	shortcut parsing and key codes; `SendInput` on Windows
`touchpad/evdev.rs`, `touchpad/tracker.rs`	evdev event parser (pure, tested on every OS); fingers and button state
`touchpad/raw.rs`, `hook.rs`, `brightness.rs`, `hud.rs`, `tray.rs`, `ui/`, `app.rs`, ...	Windows: Raw Input, mouse hook, WMI, on-screen display, tray, settings window
`linux/`	Linux: device discovery, daemon loop, uinput output, corner actions, settings web server and page

build.rs embeds the Windows manifest (per-monitor DPI, visual styles), version info and an icon generated from the same drawing code the tray uses. A GitHub Actions workflow tests on Linux and Windows and builds the release binaries when a v* tag is pushed.