Hornet

A four-player chess engine for chess.com-style 4-player Free-For-All, with a native viewer so you can play against it and watch it think.

Under the hood it's built from one primitive — per-piece line projection feeding a query engine that returns a per-player utility vector V = ⟨U₁, U₂, U₃, U₄⟩ to a Max^n search. The evaluation is a vector, never a scalar: search backs up each player's components without ever collapsing them.

Status: pre-alpha. It plays a full game and puts up a fight, but it's early and rough edges are expected. Feedback welcome.

Curious what makes four-player chess a hard problem, and which research this engine stands on? See ABOUT.md — the reading list behind the project.

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Play it

No coding required. You'll install one free tool (Rust), download Hornet, then build and run it — about 10–15 minutes, most of it just waiting on the build to finish. The steps below are written for Windows; macOS / Linux notes are called out where they differ. If you've never done any of this, that's fine — follow it line by line.

Step 1 — Open a terminal (a terminal is just a window where you type commands)

• Windows: click Start, type PowerShell, and open it.
• macOS: press ⌘ + Space, type Terminal, press Enter.
• Linux: open your Terminal app.

Step 2 — Install Rust (the free toolkit that builds Hornet)

Open https://rustup.rs in your web browser, then:

• Windows: download rustup-init.exe and double-click it. A black window opens — just press Enter to accept the default option (1) and wait for it to finish. If it says it needs the Visual C++ Build Tools ("Desktop development with C++"), say yes and let it install — that's the piece that turns code into a program your computer can actually run.
• macOS / Linux: copy the one-line command the page shows you, paste it into your terminal, press Enter, and accept the defaults.

When it's done, close the terminal window and open a brand-new one (it only "sees" Rust in a fresh window). To check it worked, type this and press Enter:

cargo --version

You should see a version number (something like cargo 1.9x.x). If you instead see "command not found", close the terminal, open a fresh one, and try again.

Step 3 — Download Hornet (the easy way — no extra tools needed)

1. Go to https://github.com/FreyjaNellora/Hornet.
2. Click the green Code button, then Download ZIP.
3. Unzip the file (Windows: right-click it → Extract All). Note where it lands — for example Downloads\Hornet-main.

(Already have git? You can instead run git clone https://github.com/FreyjaNellora/Hornet.git.)

Step 4 — Point your terminal at that folder

In the terminal, type cd (the letters c, d, then a space), then drag the unzipped Hornet folder onto the terminal window — it fills in the path for you. Press Enter. (Or just type the path yourself, e.g. cd Downloads\Hornet-main.)

Step 5 — Build it — this turns the code into a program. The first build takes a few minutes; that's normal:

cargo build --release

Lots of lines scroll past. When you see Finished near the end, it worked.

Step 6 — Play:

cargo run -p hornet-view --release

A window opens with the board and the engine starts on its own. That's it — pick your color, click New game, and play (see How to play below).

Coming back later? You only do the setup once. Next time: Windows — open the Hornet folder and double-click play.bat. macOS / Linux — cd into the folder and run the Step-6 command again.

If something goes wrong

• cargo: command not found — close the terminal and open a new one (Rust only appears in terminals you open after installing it). Still nothing? Re-run the installer from https://rustup.rs.
• A build error mentioning a "linker" or link.exe (Windows) — the Visual C++ Build Tools were skipped during Rust's install. Install the "Desktop development with C++" workload (through the Visual Studio Installer), open a new terminal, and run cargo build --release again.
• A build error saying your Rust is too old, or something about an "edition" — run rustup update, then build again (Hornet needs Rust 1.85 or newer).
• Linux: the window won't open — install your distro's desktop graphics libraries (on Debian/Ubuntu: libxcb1 libxkbcommon0 libgl1).

How to play

• In the left panel, under You:, click the color you want to play (Red, Blue, Yellow, or Green). Hornet plays the other three seats.
• Click New game.
• On your turn, click one of your pieces, then click where it should go (legal destinations show as dots).
• Pause / Step freeze the engine so you can study a position; the right panel shows its candidate moves, the expected line, and the score breakdown (what it's thinking).
• Brain scan (live), in the right panel, streams the engine's effort level-by-level while it thinks — a running record of every "thought" of the game (Copy exports the whole thing).
• Set search depth with 4 / 8 / 12 / 16 — higher is stronger but slower.

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Develop & test

cargo test --release                 # the engine test suite
cargo run -p hornet-view --release   # the viewer (after a build)

The engine speaks a simple line protocol over stdin/stdout (newgame, go depth N, move e1-f3, board, status, eval, …), so you can also drive it directly without the viewer.

Layout

Path	What
hornet-engine/	The engine crate (zero runtime dependencies — std only).
hornet-view/	The native viewer (egui). A pure display layer: it spawns the engine and relays moves, but never makes a game decision itself.

License

See LICENSE.