collin/mahjong

d5af31aa6402b7f6acea8dcf81a2794ae24c5319 / README.md

1	# 台灣麻將 — four-player mahjong, on one touchscreen or over the wire
2
3	Sixteen-tile Taiwanese mahjong for four people sitting around a single laptop.
4	All four hands are on screen at once, each rotated to face its own edge — put a
5	piece of card or plastic over your strip so the others can't see your tiles.
6	Every label is Chinese with English underneath; the tiles themselves stay
7	Chinese, because that is what the tiles say.
8
9	Nobody else around? 單人對局 Single player on the lobby gives you the
10	bottom seat and hands the other three to the computer — same rules, same
11	table, same scoring. See [computer players](#computer-players).
12
13	Friends elsewhere? 線上對戰 Online game puts everyone at the same table
14	from their own devices, and 手機派對 Party mode keeps the laptop as the
15	table while phones scan a QR to hold their own tiles — see
16	[playing online](#playing-online).
17
18	```
19	npm install
20	npm run dev # then open the browser full-screen (F11)
21	npm test # rules engine, the bots, and 200 randomly-played hands
22	```
23
24	## Screen layout
25
26	```
27	┌──── 對家 (rotated 180°) ────┐
28	上家 (rotated 90°) │ wall, and the discard pool │ 下家 (rotated −90°)
29	└──── 自家 (upright, near you) ┘
30	```
31
32	Seat 0 is the bottom edge, and play runs 0 → 1 (right) → 2 (top) → 3 (left),
33	which is the normal counter-clockwise 東南西北 order.
34
35	Each strip shows, from the player's edge inwards: nameplate (seat wind, 莊
36	marker, 聽 badge, chip count) → concealed hand → action buttons → melds and
37	flowers. Discards are not in the strips: they are thrown into the middle and
38	stay there for the hand, the way they would be on a table. (A phone has no
39	middle to throw into, so the compact layout keeps a discard row per seat — see
40	[on a phone](#on-a-phone).)
41
42	## Playing
43
44	- The tile you just drew is held apart from the sorted hand with a gold ring
45	and a 摸 label, instead of being sorted invisibly into it. It merges into the
46	hand once you discard. 補花 replacements and kong replacements are marked the
47	same way.
48	- The wall is drawn in the centre as a square of four staggered sides, laid
49	out like a `#` the way it is built on a real table — every corner covered by
50	one wall carrying past the end of the next. All 144 tiles, at the size of the
51	tiles in your hand, because they are the same tiles. The gold stack is the
52	break point you draw from, and where that is depends on what the dealer threw:
53	stacks shrink to a single tile and then vanish as they are used, so the gap
54	opens wherever the dice opened the wall and grows from there. The 16-tile 底牌
55	tail at the other end is where kong and flower replacements come from, so the
56	square is eaten from both directions at once. See
57	[擲骰](#擲骰--where-the-wall-is-broken).
58	- Discard — drag a tile out of your row and it comes up out of your hand and
59	follows your finger anywhere on the table; let go and it goes in, from where
60	you let go and at the speed you let go at. Dragging along the row is still
61	arranging your hand — which of the two you meant is decided once, from whether
62	the movement is mostly along the row or out of it, and then it sticks. Let go
63	back over your own hand and the tile goes back. Tapping a tile twice, or the
64	打出 button, still works and lobs it in for you.
65	- The discard pool — every tile thrown lands in the middle and stays there
66	until the hand ends, with real weight: it skids, turns, knocks the tiles
67	already there out of its way, and comes to rest against them. Nothing is ever
68	stacked on anything — tiles are solved as rectangles, so two lying at an angle
69	lean on each other rather than overlapping. The tile still to be claimed is
70	the lit one.
71	- Over the wall or across the table — which of the two ways a tile goes in is
72	not a setting, it is whatever the wall allows. At the start of a hand the
73	square is a solid barrier and a discard has to be lobbed over it, so the
74	flick's speed decides how far across the pool it lands. As the wall is eaten
75	away, gaps open in front of one seat and then another, and from then on that
76	seat can slide a tile in instead — flat across the cloth at exactly the speed
77	it was flicked. Which it will be is a ray cast at the stacks actually standing
78	there, so a gap off to one side counts, and a stack worn down to a single tile
79	is low enough to go over. A seat whose wall is still up says 牆未開 on its
80	nameplate, so a lob is never a mystery.
81	- Throw it badly and it ends up in somebody's tiles — the middle stops
82	exactly where their hand starts, so a tile that comes off the pool arrives in
83	their lap, and one that falls short lands out by their seat. Either way their
84	row takes the knock and rocks back, and with 報牌 on they tell you about it —
85	喂，小心點 if you are lucky, 是在哈囉 or 你牌品很差欸 if you are not, and
86	never the same line twice running. How hard it got there only decides how
87	loudly. Never your own edge: you cannot be barged by your own discard.
88	- Arranging — drag any tile in your hand to reorder it; 理牌 sorts it back
89	into suit order. Hands are never auto-sorted after the deal, so an arrangement
90	you set up survives draws, claims and kongs.
91	- Rules — the `?` on your nameplate opens a bilingual rules panel anchored to
92	your own edge of the table and rotated to face you.
93	- Claiming — after a discard, every seat that can claim gets 胡 / 槓 / 碰 /
94	吃 / 過 buttons on their own strip, and they resolve by priority (胡 > 槓/碰 >
95	吃; ties go to the player nearest the discarder in turn order).
96	The table never blocks on a claim. The next player gets a 摸牌 button and
97	may draw whenever they like, which shuts the window on anyone who hasn't
98	called — exactly like shouting 碰 before the next player picks up. A claim
99	already declared still stands, so calling in time always wins the tile. If
100	everyone answers first, play advances on its own without the extra tap.
101	The seat that draws next gets no separate 過 button, because for them the two
102	are the same move: picking up is how you decline. Their draw button reads
103	過．摸牌 while they have something they could have called instead. Wanting to
104	decline but leave the window open for everyone else is just waiting, which is
105	what not pressing anything already does.
106	- On your turn — 自摸, 暗槓 and 加槓 appear automatically when legal.
107	加槓 offers everyone else a 搶槓 chance.
108	- Where the buttons go — on the same row as your tiles, at the right-hand end
109	of it, where the tile you are about to throw already is. The bar is out of the
110	strip's flow, so a button arriving moves nothing: 打出五萬 appearing when you
111	lift a tile used to shove the melds and flowers above it up the strip. Every
112	button on the bar is given one height for the same reason.
113	- On the keys — ← and → walk the selection along your hand and space throws
114	the tile that is lifted. How long you hold space is how hard it goes: the
115	tile draws back out of the hand while the key is down and leaves when you let
116	go, so a tap slides it in and a long hold sends it across the square. Escape
117	puts it back. The wall still decides whether it can be slid or has to be
118	lobbed, exactly as with a finger.
119	- When a hand ends — a big arrow drops onto the winner's edge of the table.
120	It lives inside their strip, so it turns with the seat and lands on the right
121	person wherever they are sitting, and 一炮多響 lights up every seat that
122	called. A 流局 has no winner to point at, so it turns the hands over instead:
123	who was 聽牌 and the tiles they were waiting on, the same reveal as at a real
124	table.
125	- The gear — beside the `?` on every nameplate, and it opens that player's
126	own copy of the table's controls: undo, sound, full screen, 設定. Anchored in
127	their strip and turned to face their edge, like the rules panel, so what you
128	open reads the right way up to you and to nobody else. These used to be a bar
129	in the middle of the table, which is the one place that belongs to everybody
130	— the pile lands there and it is upside down to two of the four.
131	- Undo — 復原 in that panel takes back the last action, naming what it will
132	undo (`復原玩家 2 打五萬`). It is in all four panels rather than only the
133	seat that made the mistake, because whoever spots the mis-tap should be able
134	to reach it. Twenty actions deep, cleared when the next hand is dealt.
135	Snapshots live outside the saved state, so an undo does not survive a
136	refresh: what you can take back is what happened while everyone was still
137	watching it happen.
138	- Sound — on by default, muted from the 🔊 button behind any seat's gear, or
139	from settings. A dry clack as a tile goes down, and a distinct
140	two-note chime when a claim window opens, which is how a slow player notices
141	their 碰 is available before the next player draws it shut. Everything is
142	synthesised with a few oscillators (`src/game/sound.ts`) rather than sampled,
143	so there is nothing to load and the cue lands on the same frame as the tile.
144	Browsers refuse to start audio before the page has been clicked, so the first
145	sound anyone hears is the deal — triggered by the button that starts it.
146	- 報牌 (voice) — a second switch under sound calls the game out loud: 碰,
147	吃, 槓, 胡了, 自摸, and the name of every tile as it is discarded — 三條,
148	五萬, 東風. A flower says 補花 and then which one. A new call cuts off one
149	still being spoken; at table pace the newest is the only one that matters.
150	See [the voice pack](#the-voice-pack) for where the audio comes from.
151	- 方位音 (sound by seat) — a third switch, on by default. Every noise comes
152	out of the edge its seat is sitting at: 上家 to your left, 下家 to your right,
153	and 對家 across the table, where it is quieter and has the top taken off it —
154	a metre of air and three people's arms do not carry 12 kHz. So you can tell
155	whose 碰 that was without looking up, which is the whole point of hearing it.
156	Tiles out in the middle are placed properly rather than by edge: the physics
157	knows to the pixel where a tile landed, and that is where the knock comes
158	from. Online the table is turned so your own seat is at the bottom, and the
159	sound turns with it. See [audio, by seat](#audio-by-seat).
160	- Settings — 設定 from the lobby, or from the game-over panel: player names,
161	底 / 台 / starting chips, the house-rule switches below, and sound. Kept in
162	`localStorage` separately from the save, so they carry over to the next game.
163	Stakes are locked once a game is under way — they'd otherwise rewrite chips
164	already won.
165
166	## Playing online
167
168	Two networked modes, both built on a room relay of our own — `server/rooms.ts`,
169	a couple hundred lines of Node on `ws`. The relay knows nothing about mahjong:
170	rooms with codes, host election by join order, one bag of shared state only the
171	host may write, and events fanned out to everyone else. One client — the
172	host — runs the engine, publishes the whole `GameState` as room state after
173	every move, and plays intents the other devices send as events. The engine was
174	already a pure JSON state machine, so nothing in `src/game/` knows the network
175	exists — the same trick `autoplay.ts` plays, stretched over a wire. The client
176	end of the wire is `src/net/room.ts`; the rest of `src/net/` is the game
177	riding it.
178
179	- 線上對戰 Online game — everyone on their own device. Whoever opens the
180	room picks 線上對戰 and gets a seat lobby; friends who open the same link
181	land in it, sit down, and the host deals. Empty seats go to the computer,
182	which runs on the host client — that is what stands in for a server on the
183	classic (free) tier. Each screen draws the same full table, turned so your
184	own seat is the bottom edge; other people's tiles are face down. Joining
185	mid-game takes over a vacant or computer seat, so a dropped friend can
186	reload and carry on.
187	- 手機派對 Party mode — the laptop stays the table, exactly like hotseat,
188	and each seat's corner of the felt wears a QR. Scanning one loads a
189	controller on the phone: just that hand, face up, with the claim buttons —
190	and the throw. Flick a tile up off the top of the phone and it sails in from
191	your edge of the common screen, at the speed and angle you let go of it
192	(`NetThrow`, mapped into table coordinates by `TablePool.throwFromNet`). The
193	seat's tiles go face down on the shared screen and its QR hides; hold the 📱
194	tag on the nameplate to show it again for a player who lost theirs. A phone
195	that leaves hands the seat back to the laptop. Seats never lock: a second
196	phone scanning the same QR joins the same hand — two people playing one
197	hand, whoever acts first acts. And with sound on, the phone in your hand is
198	what says your calls — see [audio, by seat](#audio-by-seat).
199
200	Design notes, in the order they bit:
201
202	- Seats are claims on a shared map, `seats: {ids, name}[]` in room state,
203	arbitrated by the host. Your own hand's arrangement never goes over the wire
204	— the state carries a multiset and each device keeps its own order
205	(`src/net/handOrder.ts`), because a round-trip inside a drag gesture is lag
206	you can feel.
207	- The host can change. The relay re-elects — the earliest joiner still
208	connected — when the host leaves; every other client already mirrors the
209	full state, so the new host starts its engine from what it was just watching
210	and the game carries on.
211	- A hidden host must keep hosting. Browsers suspend requestAnimationFrame
212	and throttle timers in background tabs, so nothing in `src/net/` runs on a
213	loop: state writes flush on a microtask, everything inbound arrives over the
214	WebSocket (whose delivery is not throttled), and dead connections are the
215	server's ping loop's problem. A party screen somebody tabbed away from
216	keeps answering.
217	- Identity is a UUID in sessionStorage, chosen by the device and taken at
218	its word by the relay. The seat map is keyed on it, so a reload or a wifi
219	blip walks back into its own seat. No auth — this is a home server for one
220	table of friends.
221	- Fairness is social, not cryptographic. Room state carries the whole
222	game, wall and hands included — a friend with devtools open can cheat.
223	Moving the engine into the relay would fix that; the server is ours now, so
224	only the work stands in the way (TODO).
225
226	### Running it
227
228	```
229	npm run dev # vite, with the relay on /ws of the same origin
230	npm run build && npm run serve # production: dist/ + relay, one process
231	```
232
233	The relay always lives at `/ws` on the page's own origin. In development
234	`vite.config.ts` attaches it to vite's server, so `npm run dev` is the whole
235	stack; in production `server/index.ts` serves the built `dist/` and the relay
236	from one port (`PORT`, default 8080), listening on the LAN by default so
237	phones on the same wifi can scan straight in. Anything further away wants TLS
238	in front — a reverse proxy with a certificate — since phones only get camera
239	and fullscreen on https.
240
241	Rooms live in memory. A restart drops them; the next visitor on an old link
242	recreates the room empty, and a host mid-game republishes its state on the
243	next move. Joining a room writes `?room=` back into the address bar, so the
244	page URL — the host's included — is the invite link.
245
246	A QR pointing at `localhost` is a QR only the host's machine can scan, so the
247	server always gives the invite links a public face: `PUBLIC_URL` if set, else
248	it runs its own rsgrok tunnel (the house ngrok replacement) — spawned
249	the moment the server knows its port, the https URL read off the tunnel-up
250	line, no `:4040` inspection API (another agent may own that port). Every QR
251	and invite link wears that origin instead of the page's. If the tunnel dies,
252	or `rsgrok` is not on the PATH (`RSGROK_BIN` points elsewhere), links fall
253	back to the page's own address and the tunnel is retried on later joins.
254
255	The tunnel always asks for the same subdomain — `mahjong-table`, or whatever
256	`TUNNEL_NAME` says — so restarts land back on the URL people already have
257	instead of burning a fresh name each run. A name someone else already holds
258	kills that first attempt before it prints a URL; the retry then goes out
259	nameless and takes whatever it is given.
260
261	## On a phone
262
263	The table assumes four people sitting around a screen lying flat, and about
264	770px in both directions before the middle is worth looking at. A phone has
265	neither, so under `(max-height: 620px), (max-width: 820px)` it switches to the
266	compact layout: nothing is rotated, everything reads upright for the one person
267	holding it, the other three seats shrink to cards showing what is public about
268	them, and the depth that frees up goes to your hand, which is allowed to wrap.
269
270	There is no centre square there — the middle collapses to a one-line bar showing
271	what the wall square was telling you anyway — so there is nowhere to throw a tile
272	to. The compact layout therefore keeps a discard row per seat, and discarding
273	is tap-twice or 打出, exactly as it was. The pool and the throw are a full-size
274	feature.
275
276	The breakpoint is written down once, in `COMPACT_QUERY` in `src/ui/compact.ts`,
277	which sets a `compact` class on `<html>` for the CSS to key off.
278
279	## Computer players
280
281	Single player seats you at the bottom and gives seats 1-3 to the computer.
282	Their tiles go face down and their 聽 / 過水 badges come off, since both would
283	give the hand away; everything public — the pool, melds, flowers, chips — stays
284	exactly as it is, and everyone turns their hand over when the hand ends. They
285	throw their tiles in like anyone else, and under the same rule: a computer seat
286	whose wall is open slides them across, and one still walled in lobs them over.
287
288	The engine does not know the bots exist. `AutoPlay` (`src/game/autoplay.ts`)
289	watches the same state the screen does, and when the seat being waited on
290	belongs to the computer it calls the identical method the button would have
291	called — `discard`, `respond`, `declareConcealedKong`. So scoring, sound,
292	saving, 過水 and 包牌 all work without a special case, and a bot cannot make a
293	move a person could not. It never acts for you and never closes your claim
294	window: if the table is waiting on you, it waits.
295
296	How they play (`src/game/bot.ts`) is one idea applied everywhere. A hand is
297	judged at its resting size — the (5 − melds) × 3 + 1 tiles you hold between a
298	discard and your next draw — by its 向聽 first and by its 進張 count second.
299
300	- Discard — try every distinct tile, keep the one that leaves the best
301	resting hand. Ties go to whatever is hardest to build on: a lone honour with
302	most of its copies already gone, before a lone 五萬 that still has neighbours
303	to meet.
304	- 碰 / 吃 — only when the hand that comes out the other side is strictly
305	closer to home. Melding costs concealment and flexibility, so a claim that
306	merely holds the 向聽 steady is declined — which is why the bots pass on
307	pungs that would narrow a two-sided wait to a single tile.
308	- 槓 — judged more kindly: it pays 台 and fetches a replacement, so standing
309	still is good enough.
310	- 胡 — always taken.
311
312	What they watch you do (`src/game/danger.ts`) is the other half. Efficiency
313	alone throws whatever is fastest and pays for it; these bots read the table
314	first, off the face-up table only — discard rows, exposed melds, the 過水 locks
315	the nameplates already show. Two separate questions:
316
317	- How close does each seat look? Turns taken (a hand is usually settled
318	inside ten goes each, long before the wall looks finished, so counting the
319	wall is the wrong clock), melds exposed, and what they have been throwing
320	lately. Nobody discards 五條 out of a hand that still needs shaping — it comes
321	out once the shape is done, so late middle tiles are the tell. A 過水 lock is
322	a confession: to be locked out of a tile you had to have been able to win on
323	it.
324	- How likely is this tile the one they want? An honour can only be caught by
325	a pair or a triplet; a 五萬 sits in the middle of every run through it. A tile
326	they discarded themselves was not their tile when it went down — not proof
327	now, but the best evidence there is. A tile with no copies left unseen cannot
328	be a pair or triplet wait at all. Two melds in one suit means stay out of that
329	suit. And two dragon pungs down means the third dragon is not going anywhere
330	near the table, because 包牌 bills the feeder for the entire hand.
331
332	Whether any of that changes the discard depends on the bot's own hand. At 聽牌
333	it pushes — nothing short of 包牌 is worth breaking a ready hand for. Two or
334	three away with somebody live across the table and it will give up a whole 向聽
335	step to throw something safe, which is what folding is.
336
337	The estimate is checked against ground truth in the tests rather than assumed:
338	over the tiles bots actually considered, the ones the model rated below 0.2 deal
339	in 0% of the time and the ones above 0.8 deal in 10.5%, cleanly monotonic in
340	between. Switching the read on cuts deal-ins by about 13% over a few hundred
341	hands, takes hands from ~30 discards to ~38, and moves the draw rate from
342	almost nothing to about one hand in ten — which is what a table where people
343	stop feeding each other actually looks like.
344
345	What they know is still only what they can see. `unseenFor` counts the four
346	copies of each tile and subtracts the bot's own hand plus every discard and
347	exposed meld on the table. Neither module ever reads an opponent's concealed
348	tiles or looks at the wall.
349
350	There is no difficulty setting, and the reading stops at the discard: claims are
351	still judged purely on speed, and a bot will take a 碰 that walks it into
352	trouble.
353
354	向聽 lives in `src/game/shanten.ts`, apart from `hu.ts`, because the two want
355	different things: the win check has to be exact, and this one has to be fast —
356	it runs a few hundred times for every discard a bot considers. The tests hold
357	them against each other over random hands, since they work in completely
358	different ways and any disagreement is a bug in the fast one.
359
360	Undo behaves differently against the computer: rewinding into the middle of its
361	turn would only hand the move straight back to it, so one press goes back to
362	the last point you had a decision to make, computer replies and all.
363
364	## Saving
365
366	The game state is plain data, so a save is just its JSON in `localStorage`,
367	rewritten after every move. Close the lid, refresh, or run the battery flat and
368	nothing is lost — the lobby offers 繼續對局 Resume above the two ways to
369	start a fresh one, showing whether it was a solo or a hotseat game, the round,
370	hand number, chip counts and when it was saved. Which seats the computer holds
371	is part of the state, so a save resumes as the kind of game it was. A
372	save is validated before it is offered (four players, 144 tiles accounted for),
373	so a truncated or hand-edited one is ignored rather than loaded into a broken
374	table. `VERSION` in `save.ts` retires old saves if the state shape changes.
375
376	## Rules implemented
377
378	- 144 tiles (four of each suit/honour, eight flowers), 16-tile hands, dealer
379	draws the 17th.
380	- 補花 at the deal and on every drawn flower, replacements from the back of the
381	wall.
382	- 吃 only from 上家; 碰/槓/胡 from anyone. 明槓, 暗槓, 加槓, 搶槓, 槓上開花.
383	- 流局 when 16 tiles remain (`Rules.wallReserve`); the dealer keeps the deal on a
384	draw or on a dealer win (連莊), otherwise the deal passes and the round wind
385	advances every four passes. A full 四圈 game is 16 dealer passes.
386
387	### House rules (switches in `Rules`, all on the settings screen)
388
389	- 過水 `sacredDiscard` (on) — pass on a tile you could have won with and it
390	is dead to you until your own next draw; the seat shows a 過水 badge listing
391	what it is locked out of, so the missing 胡 button is never a mystery. A draw
392	from either end of the wall lifts it. `sacredClearedByClaim` (off) decides
393	whether taking a 吃 / 碰 / 槓 lifts it too — tables genuinely differ.
394	- 一炮多響 `multipleWinners` (off) — one discard pays out to every seat that
395	calls on it, each settled separately against the discarder. With it off the
396	tile goes to the caller nearest the discarder. Either way the table now waits
397	for other seats that can win before settling, so the nearest seat wins the
398	tile rather than the quickest hand — and the 摸牌 button still closes the
399	window on anyone dithering.
400	- 包牌 `liability` (on) — feeding the pung that completes a visible 大三元
401	or 大四喜 makes the feeder answer for the whole hand, in place of all three
402	payers. Only the seat that fed the last of those sets is on the hook, and
403	only if it came off a discard: a hand that assembled them itself, or closed
404	the set with a 暗槓, has nobody to blame.
405
406	### 台 scoring (`src/game/tai.ts`)
407
408	自摸 1 · 門清 1 · 門清自摸 +1 · 全求人 2 · 平胡 2 · 五門齊 2 · 正花 1 each ·
409	花槓 2 · 八仙過海 8 · 圈風 / 門風 1 each · 三元牌 1 each · 小三元 4 · 大三元 8 ·
410	小四喜 8 · 大四喜 16 · 碰碰胡 4 · 混一色 4 · 清一色 8 · 字一色 16 ·
411	三暗刻 2 / 四暗刻 5 / 五暗刻 8 · 獨聽 · 單釣 1 · 搶槓 1 · 槓上開花 1 ·
412	海底撈月 1 · 河底撈魚 1 · 天胡 16 · 地胡 16 · 人胡 8 · 莊家 1 (連N拉N → 2N+1)
413
414	Ambiguous hands are decomposed every legal way and scored at the best reading.
415
416	Payment (`Game.settle`): one unit is `底 + 台 × 台值`
417	(`DEFAULT_RULES` = 底 3, 台 1, 100 chips each).
418	放槍一家付 — the discarder alone pays one unit; on 自摸 all three pay one unit
419	each. 拉莊 is billed to the dealer alone when the dealer is a payer, and added
420	to the whole hand when the dealer wins.
421
422	House rules vary a lot; the tai table and payments are plain data/functions in
423	`tai.ts` and `types.ts` if yours differ.
424
425	## Audio, by seat
426
427	A sound at a mahjong table comes from somewhere. You know whose 碰 that was
428	because it came from your left, and you know a tile has been thrown hard at the
429	far corner without watching it go. Both of those are cheap to keep, and both
430	are gone the moment everything comes out of the middle of one screen.
431
432	Every cue is a seat's. `SoundCue` carries a `seat` alongside the kind and
433	the tile — the seat that threw, called, or won — and leaves it off the things
434	that belong to the table rather than to anybody: the deal, a 流局, an undo. The
435	engine says whose only because a sound has to come from somewhere; what that
436	means in the room is entirely the UI's business, as it always was.
437
438	A seat becomes a place. `App.tsx` turns a seat into a *position round this
439	screen* — 0 the near edge, 1 the right, 2 across, 3 the left — because that is
440	what the ear wants and the seat number is not: online the table is turned so
441	you are always at the bottom, and the sound has to turn with it.
442	`game/sound.ts` gives each position a bus of its own: a pan, a gain, and a
443	lowpass that opens all the way for the near edge and closes to 5 kHz for the
444	far one. Distance is two things at once — quieter, and with the top taken off
445	— because between you and 對家 there is a metre of air, a wall of tiles, and
446	three people's arms, none of which carry treble. Tiles out in the middle skip
447	the edges entirely and are placed continuously, panned by where on the felt
448	they actually landed; the physics knows that to the pixel. Buses are built once
449	per spot and quantised, so a pool full of skidding tiles reuses a handful
450	rather than building one per contact. Old Safari has no `StereoPannerNode`; it
451	plays where it always did.
452
453	At a party table, the words come out of the player. Five devices in one
454	room, and the split the sound should take is the one the room already has: the
455	table makes the noise, because the tiles are on the table, and the phone in
456	somebody's hand says their calls, because the calls are theirs. So the party
457	screen drops the voice for a seat while keeping the clack, and the phone
458	holding that seat says 碰 and names its own discards and makes no table noise
459	at all.
460
461	That only works if the phone really is going to say it, so it is asked rather
462	than assumed. `sound.voiceLive()` is the honest answer — sound on, 報牌 on, the
463	audio hardware awake, the pack decoded — and every device reports it to the
464	host whenever it changes (`EV_VOICE`). The host works out, seat by seat, which
465	hands have a device that will speak for them and publishes that as `voices` in
466	room state; a nameplate wearing 🔊 next to its 📱 is a seat the table has gone
467	quiet for on purpose. Mute the phone, put it to sleep, hand the seat back —
468	the flag drops and the table takes the calls back mid-hand. The host's own
469	device never counts, even when it holds seats: it is the table, and a table
470	that fell silent on the grounds that it was about to speak would say nothing at
471	all.
472
473	A browser will not start audio before the page has been touched, and a phone
474	that arrived by QR may never touch anything that asks for it by name — so the
475	first touch anywhere unlocks it, which is also the moment it can start
476	claiming the job.
477
478	## The voice pack
479
480	A mahjong table only ever says about fifty things — 42 tile names and a handful
481	of calls — so the whole vocabulary is rendered ahead of time into
482	`public/voice/` (~330 kB of mp3) rather than left to whatever speech synthesis
483	the browser happens to have. On Linux that is usually espeak-ng, which is
484	intelligible but sounds like a modem; and on a machine with no Chinese voice at
485	all the feature would silently do nothing. Shipping the audio makes playback
486	instant, identical everywhere, and lets a call be cut off mid-word when the
487	next one lands, all through the same Web Audio graph as the chimes.
488
489	`scripts/voice.mjs` is the authoring step, not part of `npm run build`. It needs
490	[piper](https://github.com/OHF-Voice/piper1-gpl) and ffmpeg on PATH:
491
492	```
493	node scripts/voice.mjs # → public/voice/*.mp3 + manifest.json
494	PIPER_MODEL=/path/to/voice.onnx node scripts/voice.mjs # a different voice
495	```
496
497	The wording lives in that script, and some of it is deliberately not the bare
498	tile character: 東 alone is a direction where 東風 is the tile, and the dragons
499	are 紅中 / 發財 / 白板 the way they are actually called — which also gives the
500	phonemiser enough context to get the tone right, since 中 on its own is as
501	likely to come out zhòng.
502
503	The clips here were rendered with piper's `zh_CN-huayan-medium`. If you
504	redistribute this app, check that voice's model card in
505	[piper-voices](https://huggingface.co/rhasspy/piper-voices) for the terms
506	attached to it, the same way you would the tile art below — or re-render the
507	pack with a voice whose terms suit you, which is a single command.
508
509	## Tile art
510
511	`public/tiles/tiles.svg` is the postmodern tileset from
512	[gnome-mahjongg](https://gitlab.gnome.org/GNOME/gnome-mahjongg), extracted from
513	the installed binary's GResource — a 43×2 sprite sheet (second row is the
514	highlighted variant, used for a lifted tile). `public/tiles/back.png` is the
515	blank tile from its smooth theme, tinted jade, since a solitaire game has no
516	face-down art of its own.
517
518	How a tile is drawn on the canvas — the outline round it and the shadow under
519	it — lives in `src/ui/tileArt.ts`, and `npm run dev` serves `/tiles.html`, a
520	page of every face at every angle over the felt with a slider on each of those
521	numbers and the finished block ready to paste back. None of it can be judged
522	from the values: it is 246 white against a dark green at 35 pixels across, and
523	the only way to know is to look at it and move something. (`tiles.html` is not
524	one of the build's entry points, so it does not ship.)
525
526	The sheet is not a picture of a tile's face. It is a picture of a whole tile,
527	drawn in an oblique projection, with its own sides painted down the left and
528	along the bottom and its own light coming from the top right — a 16px bevel on a
529	128px cell. That is fine while every tile stands the same way up, and wrong the
530	moment they are scattered: rotating the sprite rotates a pre-rendered solid, so
531	a pool of discards ends up with a different sun on each tile.
532
533	So the art is cropped back to the flat face, and the solid is worked out
534	instead. A tile is a box lying on cloth: take the four corners of the rotated
535	rectangle, offset them by the projection (`depthAngle`, down and to the left,
536	the same direction the art used), and fill the two or three quads whose edges
537	the base falls away from — each shaded from the direction that edge faces *on
538	screen*. Turn the tile and the same physical side comes round to face a
539	different way and its shading changes with it, which is the whole point. No 3D
540	engine, no z-buffer: one projection vector and a dot product per edge.
541
542	Each cell of the sheet is cut out into its own canvas the first time it is
543	wanted. `drawImage` with a source rectangle is allowed to sample past that
544	rectangle when it resamples, and the row under every face is the highlighted
545	variant, whose border is bright blue — so a tile at any angle other than a right
546	one wore a blue fringe along one edge. Square on it never showed, which is why
547	it looked like a rotation bug rather than a spritesheet one.
548
549	A tile used to be drawn as two passes — a slab of ivory offset down the screen
550	with the face on top, so a sliver of the tile's own side showed along the bottom
551	edge. At the size a discard is actually drawn that never read as thickness; it
552	read as a second, paler shape stuck to the bottom of every tile. Shading it
553	better did not help, because the problem was that it was there. What gives a
554	tile its weight now is the shadow and the outline, both of which are true at
555	any size.
556
557	That art is GPL-2.0-or-later. Fine for playing at home; if you ever
558	distribute this app, either honour the GPL or swap the two files for art of your
559	own — `SPRITE_COL` in `tiles.ts` is the only mapping that would need updating.
560
561	Known gaps and house rules that aren't implemented yet are listed in
562	[TODO.md](TODO.md).
563
564	## Layout
565
566	```
567	public/tiles/ sprite sheet + tile back
568	src/game/tiles.ts tile codes, wall, shuffle, sprite mapping
569	src/game/hu.ts hand decomposition, 聽 detection, wait shapes
570	src/game/shanten.ts 向聽 / 進張 counting, for the computer players
571	src/game/bot.ts what a computer player discards and claims (pure)
572	src/game/danger.ts reading the table: who looks ready, which tiles are hot
573	src/game/autoplay.ts when it does it, and how long it appears to think
574	src/game/tai.ts 台 scoring
575	src/game/engine.ts state machine: deal, turns, claim resolution, settlement
576	src/game/ctl.ts TableCtl — the surface the UI drives, local or networked
577	src/game/wall.ts what is left of the square, and what still blocks a throw
578	src/net/room.ts the wire itself: join, reconnect, state, events
579	src/net/session.ts the room: host duties, seats, intents, migration
580	src/net/table.ts TableCtl over the wire: mirror + intents + hand overlay
581	src/net/protocol.ts what crosses the wire, in one place
582	src/net/handOrder.ts your own arrangement, kept on your own device
583	src/ui/Controller.tsx the phone at the party table: your tiles and the throw
584	src/ui/OnlineLobby.tsx seats and the deal button, before an online game
585	server/rooms.ts the relay: rooms, host election, state fan-out
586	server/index.ts production: dist/ and the relay from one port
587	src/table/physics.ts the discard pool: rectangles with weight, pure and testable
588	src/table/geometry.ts the table measured — colliders, launch points, throw gate
589	src/table/pool.ts game state ⇄ tiles in the middle, by diffing the discards
590	src/ui/ TileView, Hand (drag and throw), Seat, Center, Pool, Help
591	```
592
593	## The tiles in the middle
594
595	The pool is a small rigid-body solver (`src/table/physics.ts`) that knows nothing
596	about mahjong, the DOM, or the clock: fixed 1/120s steps, no randomness of its
597	own, and everything in table pixels. Given the same throws it produces the same
598	pile every time, which is what lets a refresh mid-hand come back to the pile you
599	had rather than a freshly scattered one — positions are derived from the hand
600	number and each tile's place in its thrower's discards, never saved.
601
602	The pile is handled directly. Press on a discard and it comes up out of the
603	pile, carried over the top of the others rather than ploughing through them;
604	let go slowly and it is set down there, flick and it goes off across the felt at
605	the speed it left your fingers — the same throw a tile gets out of a hand, made
606	from the middle of the table instead. Pressing on bare felt does nothing, and
607	the press passes through to whatever was really under it: the tiles are drawn on
608	a canvas with no elements to hit, so the hit test is against the physics and the
609	listener is a capturing one on the table itself.
610
611	A flick is the whole of a throw: the direction and the speed it leaves at are
612	the hand's, and nothing between the fingers and the felt changes either. The one
613	thing the table decides is height — with a standing wall in front of the
614	throw a flat tile would only skid into it, so it is lofted over instead, exactly
615	as far as it was thrown and simply in the air for the first part of the way. A
616	tile that carries past the square and out into the open stays there. (It used to
617	be re-aimed at the middle of the square when the flick's line missed it, which
618	put the tile on a line nobody had thrown and read, fairly, as a bounce off
619	nothing.)
620
621	What stops a tile is other tiles. There is no fence: the standing stacks of the
622	wall, the sets people have laid down and the sixteen each of them is holding are
623	all measured as colliders, so the pile is held in by the ring of tiles round it
624	exactly as it is on a real table, and spills through whatever gaps the wall has
625	been eaten into. The table's own edge is a backstop at the screen edge, there
626	only so a tile that got past all of that isn't lost.
627
628	It is drawn on a canvas that spans the whole table, not just the centre.
629	That is deliberate: `.slot` and `.seat` both clip their own contents, which is
630	why a tile can't be animated out of a strip as an element. On the canvas there is
631	nothing to clip it, so a tile lifted out of a hand crosses the table in one
632	piece.
633
634	The square is the whole wall: eighteen stacks of two a side, four sides, 144
635	tiles, the way it is built on a table. It used to be rebuilt to what was left
636	after a hand had been dealt — barely half of it — because eighteen full-size
637	stacks a side wants about 560px and no ordinary window has that between the top
638	and bottom strips. That bought a square at the price of it not being the wall:
639	a side ran out of stacks before it reached its corner, so the four of them never
640	met.
641
642	Nothing gives now, and in particular the tile does not. Every tile on the table
643	is one size — `--tile-w` in styles.css, in a hand, in the wall, and lying in the
644	middle — because they are the same tiles, and a tile that changed size between
645	the wall and your hand read as a different, smaller set sitting in the middle.
646	The square is built from that tile and is however big that comes to:
647	`wallSquare()` in `game/wall.ts` takes the tile and hands back the lengths, and
648	`WallRing` measures one rendered cell to find out what CSS made it. The wall
649	being bigger than the room between the strips is a fact about a 144-tile wall,
650	not a thing to solve by shrinking it.
651
652	The four walls are placed by CSS alone: each is pinned to its own edge of the
653	opening with `left`/`top`, runs its whole length from the corner it is built
654	from, and so carries one wall-depth past the far corner and over the end of the
655	next wall along. Every corner of the square is covered by exactly one wall and
656	no two overlap — that is the pinwheel. Nothing is rotated; a square wants no
657	rotation to describe it.
658
659	The overhang is exactly one wall-depth, which is what it takes to close a right
660	angle: two bands of thickness `t` meeting at an interior angle ψ overlap by
661	`t / tan(ψ/2)`, and at ninety degrees that is `t`. So the whole square measures a
662	wall's length plus one depth across, and leaves that length less one depth in
663	the middle — which is the opening, and which is what `.wall-ring` itself is.
664
665	The CSS only places what it is told: `.wall-side` is a row of stacks, laid across
666	on the two flat walls and down on the two upright ones, and `--wall-len` from
667	`WallRing` is the only length it is given. Every place in the wall is rendered
668	whether or not there is still a stack standing on it, because with the break
669	anywhere but a corner a wall is eaten from its middle — a row that closed the
670	gap up would drag the whole tail of the wall along the table behind it.
671
672	Where the four walls stand is found at the table itself rather than on a page
673	of sliders: take hold of a wall in a real game and push it. It goes where the
674	finger goes, and lets go saying where it landed — `[wall] top pushed to 0.5,-4.9
675	— top 0.5,-4.9 · right 0,0 · …` in the console, in tiles, which is the form
676	`WALL_PLACED` in `game/wall.ts` is written in, so what a push finds pastes
677	straight back in. Nothing about the hand moves: the wall is the same wall in the
678	same order and the next draw is still the next draw. There used to be a
679	`/wall.html` for this; the table is the honest place to do it, so that page is
680	gone.
681
682	## 擲骰 — where the wall is broken
683
684	The dealer throws three dice to open a hand, and the total does two jobs. It
685	counts round the seats — the dealer being one, and the count going the way the
686	turn goes — to pick whose wall is opened. Then the same number counts stacks in
687	from the right-hand end of that wall, and the break is behind them: the first
688	tile drawn is the next one along, and the drawing runs away to the left from
689	there, on round the square.
690
691	The square makes that cheap to say. Every wall is laid down from the corner its
692	own player's right hand falls on — that is what the pinwheel is — so the run of
693	72 places already starts at each seat's right, and the break is simply so many
694	places into the side the dice picked. `breakAt()` is those two lines.
695
696	Nothing about the tiles turns on it: the wall was shuffled before it was built,
697	so which stack is drawn first is decided either way. What it moves is where in
698	the middle of the table the gap opens and who has to reach furthest for the next
699	draw — which is the whole of what it does at a table too. The throw is made from
700	the same seeded rng that shuffled, so a seed replays a hand's gap as well as its
701	tiles.
702
703	In a dev build a panel in the corner of the table steps the total through every
704	one three dice can make, 3 to 18, and redraws the square on each; 整牆 144
705	puts every tile back, which is what the square is built to and what it only ever
706	is for the moment before the deal. `game.reroll(6, 6, 6)` does the same from the
707	console.
708	Nothing about the square is calculated twice. Its size lives entirely in CSS
709	(`--ws`, `--wd`), so `geometry.ts` measures it instead of restating that
710	arithmetic: `WallRing` already renders every stack as a real element tagged with
711	its index, and the colliders are those elements' bounding rects. That one
712	mapping is what makes the wall a physical object — the thing a thrown tile
713	bounces off, and the thing the throw gate casts its ray at.
714
715	### Seeing the colliders
716
717	Because every boundary is measured off the DOM rather than written down, the
718	only honest way to check a bounce is to draw the boxes in the coordinate space
719	the tiles are drawn in. Add `?colliders` to the address, or call `colliders()`
720	from the console while a hand is running:
721
722	\| drawn \| is \|
723	\| --- \| --- \|
724	\| solid rectangle at the screen edge \| the table itself. Nothing meets this in play — it is only there so a tile that got past everybody's tiles is still on the table afterwards \|
725	\| solid box on every tile \| a collider. Every tile on the table is one: the stacks still standing, the sets people have laid down, and the sixteen each of them is holding. Half stacks aren't drawn because they aren't colliders — a tile goes over them \|
726	\| dashed rectangle \| the wall square's opening — where a throw is aimed. It stops nothing, which is why the pile spills out of it \|
727	\| dotted rectangle, inset \| where the moving tile's own centre may be against the table's edge, which is its half width in from it \|
728	\| box hugging each pool tile \| the rotated rectangle it really collides with \|
729	\| dotted box round the moving tile \| the upright box the straight edges use instead. It comes apart from the rotated one as the tile turns \|
730
731	\| blue rays from a throw \| faint: the flick, as the tile was let go of. Bright: the line it was actually sent along, labelled `slide` or `lob`. These should lie on top of each other — the flick is the throw, and a tile leaving on a line nobody threw reads exactly like a bounce off something invisible \|
732	\| yellow cross \| where contact was actually made, fading over a second or so. One of these sitting in open felt with no box under it is a bounce off something that isn't a collider at all — a different bug from a box in the wrong place \|
733
734	Colliders mode is also a throwing sandbox: a flick throws for real but is not a
735	discard, so the tile stays in your hand, the turn never passes and the computer
736	players hold still. Throw the same tile at the same corner as many times as you
737	like. Sixty stay on the table before the oldest is swept off; `pool.clearLoose()`
738	sweeps them all. Tapping a tile to discard does nothing in this mode — throwing
739	is the thing being tested.
740
741	Add `pause=1` (`?colliders&pause=1`, or `pause()` from the console) to **stop
742	dead on contact**. The physics halts on the fixed step that resolved it and
743	drops the rest of the frame, so what's on screen is where the tile touched
744	rather than where it had got to by the end of the frame. Space carries on, →
745	takes one step, ↑ takes ten; the console says what it stopped on.
746
747	`colliders(false)` turns it off again. It repaints on toggle, so a settled table
748	doesn't have to be poked first. In a dev build `pool` is the live pool: the
749	overlay draws `pool.world.walls`, the physics' own copy rather than a fresh
750	measurement, so if what's drawn ever disagrees with the DOM it is the world that
751	went stale — which `pool.measuredAt` will show, since the stamp carries every
752	hand's shape.
753
754	## What is left of the wall
755
756	Four walls of eighteen full-size stacks want about 560px a side. No ordinary
757	window has that between the top and bottom strips, and the tile is not allowed
758	to shrink to make it fit — a tile in the wall is the same tile you play with, so
759	drawing it smaller was a visible lie.
760
761	What saves it is that nobody ever sees a whole wall: four hands come off the
762	front before the table is on screen, so barely half of it is left by then. So
763	only the stacks still standing are drawn, and they are laid out around a ring
764	cut to the middle rather than to eighteen — `ringLayout` in `game/wall.ts`
765	measures how many stacks a side can take (`WallRing` renders one hidden cell and
766	asks CSS how big it came out) and shares what is left over the four sides in
767	proportion. Every seat keeps a wall in front of it instead of the remainder
768	piling into one corner, and the order runs all the way round, so the break point
769	is still at the head of it and the 底牌 tail still at the end.
770
771	Shuffling the wall along as it is eaten costs nothing to look at, because every
772	stack shows the same green back — and it is what people do to a half-eaten wall
773	anyway.
774
775	`pool.ts` never listens for events. It diffs the discards against what it is
776	already drawing, keyed by `seat:index` — and those keys never shift, because
777	discards are only ever pushed and a claim only ever pops the one on top. So a
778	key that appeared is a tile to throw in and a key that went is a tile to take
779	off, which makes undo, 下一局, a claim and resuming a saved game all the same
780	code path. The engine has no idea any of it exists, and the save format did not
781	change.