Portes (Πόρτες)
A photorealistic 3D game of Portes, the Greek game of tavli closest to backgammon, played against the
computer. Five difficulty levels from Beginner to Expert, plus a level-10 coach, Mr. Makis, who plays
the best move he can find on your board and explains why.
No accounts, no ads, no tracking, no network calls: the game is a static page and everything it remembers
(settings, scores, saved games) stays in your browser or on your phone.
Features
- Five computer levels, each measured to beat the one below it in self-play (points share 99.5%, 82.8%,
63.3%, 53.8%), from random play to a two-ply expectimax search. The evaluation was tuned by self-play.
- Mr. Makis, the coach: plays his move on your board, explains it from the position (hits and the pips
they cost, home points against a checker on the bar, blots left open and their chance of being hit, the
race) and shows the next two candidates with win estimates from play-outs. Measured against the Expert:
23 games to 17, 26 points to 23.
- Mistake review: after a game, Mr. Makis finds your costliest moves (every move scored two rolls
deep, the doubtful ones played out to the end) and shows each one in replay: the position, your move,
and his move as a what-if, with the win chance each one gives.
- Puzzles: 32 "find the best move" positions from computer games, each with an answer Mr. Makis proved
by playing every candidate to the end hundreds of times. Graded Easy to Master by which computer level
already finds the move.
- Guided lessons (the Learn button, and a welcome screen on the first visit): nine short scripted
positions on the real board, one rule each: the board and the 3-1 opening, hitting, closed points,
entering from the bar, closing the door, the larger die, doubles, bearing off, mars.
- The bar: hit checkers fly to the centre bar and must come back in before anything else moves.
- Phone layout: in landscape the board comes first, with a drawer for everything else; drag a checker
to move it.
- Hint, Undo (a hit checker goes back too), an optional opening throw, match to 5,
auto-end turn, winning chances, Admit loss / Computer quits as a single or double.
- Game records: the last five games kept automatically, up to ten named saves, move-by-move replay,
Continue from here, and
.vbg files to share a game (every move of an imported file is re-checked by
the rules engine).
- Ten board styles (woods and marbles), a room dimmer, a retro lamp with a pull-chain switch, free or
locked camera, point numbers, favourite setups you can save and export (
.vbs).
- Strategy guide (English and Greek) built from 3,000 computer-vs-computer games: hitting, your home board,
blots, the race, how games end. Every figure is generated by
test/strategy-stats.mjs and checked by
test/strategy-check.mjs.
- And, for the bad days, Slam!: fold the board shut with a bang. The game carries on exactly where it was.
Rules as implemented
From bkgm.com ("Portes") and Wikipedia ("Tavli"):
- 15 checkers each in the backgammon start (2 on your 24-point, 5 on 13, 3 on 8, 5 on 6). The two sides
travel in opposite directions towards their own home boards.
- A point with two or more opposing checkers is closed. Landing on a single opposing checker (a blot)
hits it to the bar. One checker playing both dice touches down on the point between: that point
must be open, and a blot there is hit.
- Bar first: while you have a checker on the bar nothing else moves. A die
d enters it on the
opponent's home board (your point 25 − d); if only one checker can come in, the rest of the roll is lost.
- Play both dice if you can (four moves on doubles); if only one can be played, the larger.
- Bear off once all 15 are in your home board (a checker on the bar counts as outside), exactly or with a
higher die from your furthest-back point.
- A win is 1 point; mars (the loser has borne off nothing) is 2. There is no triple game and no
doubling cube.
src/engine.js is the authority: its header lists the rules, and test/rules.mjs checks them with
hand-worked edge cases. test/legality.mjs re-implements the rules independently (absolute board with a
bar per colour, brute force over every die order) and checks, for every roll in thousands of positions,
that the moves the game offers are exactly the legal ones, that every play the computer can choose
replays click by click through the same turn API the board uses, and that game results agree.
PORTES_ENGINE=<path> points it at a modified engine: one-rule mutants (no bar-first, landing on two, no
hit, no larger-die rule, entering onto closed points, ...) are all caught.
Run it locally
The game has no build step. Serve the folder over HTTP (ES modules and the AI web worker do not load from
file://):
python serve.py # http://127.0.0.1:8835, with caching disabled for development
Tests
node test/rules.mjs # rules engine, edge cases, random full games, file formats
node test/legality.mjs # every legal play vs an independent brute-force rules implementation
node test/legality.mjs 12 200 # the same, a quick pass (~45 s)
node test/lessons.mjs # the guided lessons vs the engine (instant)
node test/strategy-check.mjs # the strategy guide's figures re-measured, EN/EL parity
node test/selfplay.mjs 200 1-2 2-3 3-4 4-5 # each level against the one below
node test/makis.mjs 40 120 # Mr. Makis against the Expert (slow)
node test/make-puzzles.mjs 8 8 150 40 # regenerate src/puzzles.js (worker threads)
node test/strategy-stats.mjs 3000 4 # the figures quoted in the strategy guide
test/browser-harness.mjs plays whole games through the page in a browser and checks the 3D board (both
bars included) against the engine after every turn (instructions in its header).
Project layout
| Path | What |
|---|
index.html | Page shell, HUD, sheets, styles; the import map points three at vendor/. |
src/engine.js | Pure rules and AI (no DOM): legality with hits and the bar, the interactive turn API, full-turn enumeration, evaluation, the five levels and Mr. Makis's analysis. |
src/ai-worker.js | Runs the computer's choice and Mr. Makis off the main thread. |
src/main.js | Renderer, board and checker geometry (the bar on the centre rail), animation, input, turn flow, HUD, settings. |
src/records.js | Game records, move notation, .vbg / .vbs file formats with validated import. |
src/textures.js, src/themes.js | Procedural wood and marble textures; the ten board styles. |
src/lessons.js | The nine guided lessons as pure data: positions, rule text, goals and answers. |
src/puzzles.js | The puzzles, generated by test/make-puzzles.mjs. |
src/effects.js | Visual effects: the computer's last-move trails and the win confetti. |
src/sound.js | Synthesised sounds (no audio files). |
strategy.html | The strategy guide (standalone page, English and Greek). |
vendor/ | three.js r170 and three of its example modules (see THIRD-PARTY-NOTICES.md). |
app/ | Capacitor wrapper that packages the game as an Android app. |
test/ | Rules tests, the legality audit, self-play matches, the tuner, puzzles and the guide's statistics. |
Build the Android app
Requirements: Node 18+, JDK 21 and the Android SDK (platform 35, build-tools 35).
cd app
npm install
node sync-web.mjs # copies index.html, strategy.html, src/ and vendor/ into app/www
npx cap add android # first time only; afterwards: npx cap sync android
node make-icons.mjs # draws the launcher icons and splash into the Android project
node patch-android.mjs # MainActivity: immersive landscape, keeps the phone's font size from scaling the HUD
cd android
./gradlew assembleDebug # -> app/build/outputs/apk/debug/app-debug.apk
In the app the strategy guide opens as a full-screen sheet over the game, and file exports are not
available (Android's WebView does not download files); importing .vbg / .vbs files works.
Licence
MIT. three.js is MIT-licensed as well; see THIRD-PARTY-NOTICES.md.
