HydroChess WASM

A high-performance Rust chess engine compiled to WebAssembly, designed for Infinite Chess variants.

📚 Documentation

Document	Description
Setup Guide	Install Rust, wasm-pack, and build the engine
Contributing Guide	Workflow for adding features and testing changes
SPRT Testing	Run strength tests to validate engine changes

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✨ Features

Search

• Iterative deepening with aspiration windows
• Alpha-beta pruning with principal variation search
• Null move pruning and late move reductions (LMR)
• Transposition table with Zobrist hashing
• Killer moves and history heuristic for move ordering
• Quiescence search for tactical accuracy
• Static Exchange Evaluation (SEE) for capture pruning
• Lazy SMP Multithreading: Scalable parallel search with runtime implementation dispatch

Evaluation

• Material counting with tuned piece values
• Piece-square considerations for positional play
• King safety evaluation
• Pawn structure analysis (isolated, doubled, passed pawns)
• Endgame detection with specialized mop-up evaluation
• Insufficient material draw detection

Infinite Chess Support

• Coordinate-based board: Arbitrary positions (not limited to 8x8)
• Fairy pieces: Amazon, Chancellor, Archbishop, Centaur, Hawk, Knightrider, Rose, Huygen, and more
• Variant-specific evaluation: Chess, Confined Classical, Obstocean, Pawn Horde, Palace

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🚀 Quick Start

# 1. Install Rust and wasm-pack (see docs/SETUP.md for details)
rustup target add wasm32-unknown-unknown
cargo install wasm-pack

# 2. Build for browser (Single-threaded)
wasm-pack build --target web

# 3. Build for browser (Multi-threaded / Lazy SMP)
node build_mt.js

# 4. Output is in pkg/ - ready for use with your bundler

For detailed setup instructions, see docs/SETUP.md.

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📖 Usage

JavaScript API

import init, { Engine } from './pkg/hydrochess_wasm.js';

await init();

const engine = new Engine(gameStateJson);

// Get best move with time limit (milliseconds)
const result = engine.get_best_move_with_time(500);
// Returns: { from: "5,2", to: "5,4", promotion: null, eval: 34 }

// Get all legal moves
const moves = engine.get_legal_moves_js();

Multithreaded usage (Lazy SMP)

To use parallel search, you must initialize the WASM module's thread pool and set the desired number of threads:

import init, { Engine, initThreadPool } from './pkg/hydrochess_wasm.js';

await init();

// Initialize thread pool (e.g., 2 threads)
await initThreadPool(2);

const engine = new Engine(gameState);
const result = engine.get_best_move_with_time(1000); // Now uses 2 threads

Note

Parallel WASM requires specific HTTP headers (Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp) to be served by your web server.

Game State Format

const gameState = {
    board: {
        pieces: [
            { x: "1", y: "1", piece_type: "r", player: "w" },
            { x: "5", y: "1", piece_type: "k", player: "w" },
            // ... all pieces
        ]
    },
    turn: "w",
    special_rights: ["1,1", "5,1", "8,1"],
    en_passant: null,
    halfmove_clock: 0,
    fullmove_number: 1,
    move_history: [
        { from: "5,2", to: "5,4", promotion: null },
        // ... moves played
    ],
    game_rules: {
        promotion_ranks: { white: ["8"], black: ["1"] },
        promotions_allowed: ["q", "r", "b", "n"],
        win_conditions: { white: ["checkmate"], black: ["checkmate"] }
    }
};

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🧪 Testing

# Run all unit tests
cargo test --lib

# Run with coverage
cargo llvm-cov --lib

# Run perft tests (move generation validation)
cargo test --test perft

For testing engine strength changes, see sprt/README.md.

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📄 License

This project is licensed under the GNU General Public License v3.0 - see LICENSE for details.

🔗 Links

• Infinite Chess - Play infinite chess online
• Chess Programming Wiki - Engine development resources
• Stockfish - The world's strongest open-source chess engine