Breakthrough

A browser version of the abstract strategy game Breakthrough, with a built-in AI opponent. Pure TypeScript, runs entirely in the browser — no install, no server, no account.

▶ Play: https://MartinMSPedersen.github.io/Breakthrough-Web/

The game

Breakthrough is played on an 8×8 board. Each player starts with two rows of identical pieces.

• Move one square straight or diagonally forward into an empty square.
• Capture only diagonally forward (never straight).
• Win by landing any piece on the far edge of the board — or by capturing every enemy piece.

Dead-simple rules, genuinely deep play. White moves up the board, Black moves down.

Playing

• Click a piece to select it (legal destinations highlight green), then click a square to move — or drag and drop.
• Mode — play the engine as White or Black, watch it play itself (Two Machines), or play a friend on the same screen (Human vs Human).
• Engine depth — higher is stronger but slower. 4 is instant; 8–10 plays a tough game.
• Vary engine play — on by default, so the engine doesn't play the exact same game every time. Turn off for fully deterministic, repeatable play.
• Themes — Classic, Slate, High Contrast, Sepia.
• Save / Load — export the game to a .game file or load one back. The format is compatible with the original desktop (Java) version.
• Undo, Flip board, and an optional engine output log showing the search depth, score, and principal variation.

The AI runs in a Web Worker, so the board stays responsive while it thinks.

Running locally

npm install
npm run dev      # builds + serves on http://localhost:8000 (live reload)

Static build (what gets deployed):

npm run build:web   # outputs to dist/web/

Deploying to GitHub Pages

A GitHub Actions workflow (.github/workflows/deploy.yml) builds and deploys on every push to main. No build artifacts are committed — CI builds from source.

First-time setup: in the repo, Settings → Pages → Source → GitHub Actions, then push to main. The site goes live at https://<user>.github.io/<repo>/.

Tests

The engine is verified against the original Java implementation:

npm run perft         # move-generation & hashing correctness
npm run search-test   # search verification

perft counts the game tree's leaf nodes from the start position; it produces exactly 6,182,818 at depth 5, matching the reference engine. The search explores an identical node count to the Java original at every depth — strong evidence the port is exact, not just approximately right.

How it's built

A faithful TypeScript port of a Java engine:

• Board — two 64-bit bitboards (bigint), incremental Zobrist hashing.
• Search — negamax with alpha-beta, iterative deepening, a transposition table, killer-move ordering, principal-variation search, and a quiescence search tuned for Breakthrough's winning-push tactics.
• UI — a <canvas> board, the engine in a Web Worker, plain DOM controls. No framework.

See ARCHITECTURE.md for the module layout and porting notes.

License

MIT — see LICENSE.