Pin

A tiny Windows system-tray utility that lets you "pin" any window so it stays on top of other windows. Inspired by DeskPins, rewritten in Rust.

How it works

1. Launch pin.exe — a pin icon appears in the system tray.
2. Left-click the tray icon — your mouse cursor turns into a pin (pin_off). You are now in selection mode.
3. Click any window — that window becomes topmost and a small pin badge (pin_on) appears at the right side of its title bar, just left of the minimize button.
4. Click the pin badge — the window is unpinned and the badge disappears.
5. Right-click the tray icon — opens a menu with Unpin all and Quit.
6. In selection mode you can press Esc or right-click anywhere to cancel.

The pin badge follows the target window as you move/resize it (~60 fps).

Build

Requires Rust stable, Windows target.

cargo build --release

The binary is at target/release/pin.exe.

Tagged releases are built by GitHub Actions. Pushing a v* tag builds the Windows release binary, packages it as an MSI installer with WiX/cargo-wix, and uploads pin-<tag>-windows-x64.msi to the GitHub Release.

Cross-compile from Linux/WSL works too:

rustup target add x86_64-pc-windows-gnu
cargo build --release --target x86_64-pc-windows-gnu

Test

cargo test

There are ~20 unit tests covering icon decoding, geometry math, and pin-set state transitions; plus two Windows-only integration tests that exercise SetWindowPos/GetWindowLong against a real hidden window.

Run with logs:

set RUST_LOG=debug
cargo run

Architecture

src/
  main.rs       — entry point (just calls pin::run)
  lib.rs        — module declarations
  app.rs        — main message loop, owns PinnedSet/Tray/Picker
  tray.rs      — system-tray icon + right-click menu (tray-icon crate)
  selection.rs  — "selection mode": transparent capture window + SetSystemCursor
  overlay.rs    — floating pin_on badge: layered topmost window + 16ms timer
  pinned.rs     — OS-agnostic pin/unpin set (testable with FakeApi)
  win.rs        — Win32 thin wrapper + WindowApi trait for testability
  resources.rs  — embedded PNG/ICO + decode/resize/BGRA helpers
tests/
  integration_pin.rs — Win32 round-trip test of WS_EX_TOPMOST

Key Win32 design choices (cross-referenced against DeskPins source for prior art):

• Selection mode: 1×1 transparent topmost popup + SetCapture to catch the click, plus SetSystemCursor/SystemParametersInfo(SPI_SETCURSORS) to swap the global cursor (the only reliably visible mechanism for a hidden popup).
• Overlay: WS_EX_LAYERED + UpdateLayeredWindow with premultiplied BGRA so the transparent PNG renders correctly. A 16ms SetTimer repositions the badge over the target and re-applies HWND_TOPMOST if the target has been knocked off the topmost group.
• No DLL injection / no global hooks — everything runs in one process via standard Win32 APIs.

License

AGPL-3.0-or-later.