horizon/docs/windows-arm64.md

Windows ARM64

Horizon builds the game and launcher as native Windows ARM64 executables for aarch64-pc-windows-msvc. GitHub Actions builds and checks them on a Windows ARM64 runner.

Build from source

Use Windows 11 on ARM, or cross-compile from Windows x64. Install stable Rust, the aarch64-pc-windows-msvc Rust target, Visual Studio C++ build tools for ARM64, and a Windows SDK with ARM64 libraries. Install LLVM/Clang and put clang.exe on PATH; the ring dependency uses Clang to compile its ARM64 code. The MSVC target also needs the Visual C++ linker and Windows import libraries.

To run horizon-prepare compile-exporters, install JDK 25 and Python 3.10+; that command compiles the Java exporters used by the game.

rustup target add aarch64-pc-windows-msvc
cargo build --release --locked --target aarch64-pc-windows-msvc `
  -p horizon-client -p horizon-client-lib --bin horizon-client --bin horizon-ctl `
  -p horizon-prepare --bin horizon-prepare -p horizon-server --bin horizon-server

The launcher has a separate workspace:

cd launcher
cargo test --release --locked --target aarch64-pc-windows-msvc --lib
cargo build --release --locked --target aarch64-pc-windows-msvc

Releases and limitations

The game archive, horizon-windows-arm64.zip, is attached to the Nightly release and listed in its signed SHA256SUMS. The launcher archive, horizon-launcher-windows-arm64.zip, and horizon-launcher-setup-arm64.exe are attached to the launcher releases and listed in their signed SHA256SUMS.

Launcher updates always follow the launcher's own process architecture. Game architecture is a separate choice in Settings on native Windows ARM, detected from the machine even when an x64 launcher runs under emulation. Automatic preserves existing behavior: an x64 launcher uses x64, and an ARM64 launcher prefers ARM64. Either launcher can choose x64 or ARM64 for the game. The choice is saved and used for installs and updates; when a release has no ARM64 archive, ARM64 selection safely installs the signed x64 fallback. A changed choice installs the selected version again when automatic updates are on; otherwise use Install selected build on the Versions page. Launching is blocked with an explanation if a manual choice does not match the installed game. Choosing a game architecture never changes or replaces the launcher binary.

Native-mod compilers remain independent of this setting. The managed compiler currently builds x64 only; an x64 launcher cannot build native mods for an ARM64 game, and the ARM64 launcher has no matching compiler yet. The launcher refuses mismatched native-mod builds rather than producing a binary for the wrong game.

On Windows ARM64, Graphics API: Auto tries DirectX 12 before Vulkan following a device-loss observed in testing. Vulkan remains selectable in settings.

The Windows ARM64 game and launcher check in ci.yml runs only by hand (gh workflow run checks --ref <branch>); the Nightly and launcher releases build these archives on every run.