Rules

Rules — the league cabinet

Every number the sim actually runs on. If a number here and a number in src/lane/ disagree, the code is right and this file is a bug.

The shape of a game

• num_agents = 4. One seat = one lane = one quadrant of the cabinet screen. Seat s plays lane s; there is deliberately no seat→lane permutation, because the four lanes are identical by construction.
• Each lane is a 17 × 17 tile screen, drawn into one 35 × 35 tile board with a one-tile gutter: lane origins (0,0), (18,0), (0,18), (18,18).
• maxTicks = 2880 ticks = 120.0 s at 24 Hz, with a floor of minTicks = 1440: the episode does not end early on "all four lanes over" before tick 1440 — over lanes sit on their GAME OVER screen.
• 24 decision turns of turnTicks = 120 ticks (5.0 s).

Isolation — the invariant

stepLane(lane, cmd, preset, tick, par) is a pure function of one lane's own state, that lane's own action byte and that lane's own RNG stream. It takes no SimServer, reads no other lane and writes no other lane. Consequently:

• rewriting lane j's whole action-byte stream leaves every other lane's per-tick state byte-identical;
• lane i run alone in a one-lane sim reproduces its four-lane trajectory exactly;
• four lanes fed the identical action-byte stream finish with identical points, lives, screens, sprite positions and RNG draw counts — the fairness proof.

The one thing that crosses lanes is the scoreboard, and it crosses in the observation layer only: each seat sees every rival's alias, score, lives and screen and nothing else. It is composed outside stepLane and is never read back by the sim.

Units

The whole sim is integers: replays are re-simulated by the emscripten/wasm32 build of the same module the native amd64 server ran, and their per-tick gameHash chains must agree bit for bit. There is no floating point, no trigonometry and no square root anywhere in src/lane/{sim,grid,rom,maps, sprites,sim_types,sim_config,sim_state}.nim — grep-enforced by tests/test_determinism.nim.

The action byte

One byte per seat per tick, 15 legal values:

dir = cmd mod 5      # 0 stay, 1 up, 2 down, 3 left, 4 right
act = cmd div 5      # 0 none, 1 fire, 2 brake

cmd >= 15 is repaired to 0 in both the server and the replay runtime, so a corrupt byte can never desynchronise the two.

The three cartridges

Everything else — grid size, tile size, tick rate, maxTicks, minTicks, the decision cadence, the wall-clock budget, the action byte, the scoring formula and num_agents — is identical across all three, which is what makes one score scale and one budget arithmetic correct for all of them.

chomper — maze-chomp

The committed map has 120 pellets, 4 power pellets, 127 walkable tiles and one wrap tunnel across row 8 (leaving column 0 re-enters at column 16).

• Avatar: moves along corridors, turns only at tile centres, with a 6-tick turn latch (a buffered direction older than 6 ticks is discarded). brake halves speed for that tick — it is how you let a hunter commit before you do.
• Sprites: four Chasers starting at (8,4), (4,8), (12,8), (8,1). Speeds 1 250 (chasing) / 900 (fleeing) / 2 000 (returning) µu per tick. At every tile centre a chaser picks the legal direction (never a reverse unless it is the only one) minimising the tunnel-aware Manhattan distance to its target; ties break UP, LEFT, DOWN, RIGHT. Targets: H0 your tile, H1 two tiles ahead of your facing, H2 four ahead, H3 six ahead. Every scatterTicks (drawn per screen in [360, 600]) the roster flips to Scatter for 120 ticks and takes the four corners instead.
• Points: pellet 10, power pellet 50, eating a fleeing chaser 100 / 150 / 200 / 250 by chain position within one power window, screen clear +500.
• Power window: 144 ticks (6.0 s); every non-returning chaser flees and reverses once, and the chain counter resets.
• Life lost: your box overlaps a chasing/scattering chaser's box (both boxes 8 000 µu on a side, centred).
• Screen clear: every pellet and power pellet gone.

brickfall — brick-breaking

Walls on row 0 and columns 0 and 16; row 16 is the drain; 60 bricks on rows 3–6; a 3-tile paddle on row 15.

• Avatar: only left/right do anything; the paddle centre is clamped to x ∈ [18 000, 186 000].

• Ball: served from (8,12) after a 24-tick delay at BallFan[j] for j drawn from {1,2,4,5} (never straight down, never a wall-grazer).

• The fan — a committed 7-entry integer table indexed by which seventh of the paddle the ball struck. Every entry has vy < 0, so a paddle can never send the ball back into the drain, and every magnitude is within 5 % of 2 800 µu/tick:

  BallFan = [(-2600,-1200), (-2100,-1900), (-1200,-2500), (0,-2800),
             (1200,-2500), (2100,-1900), (2600,-1200)]
  

• Speed ramp: every 8 brick hits speedPermille += 50, capped at 1 400; the applied velocity is (v · speedPermille) div 1000.

• Points: brick row 3 = 50, row 4 = 30, row 5 = 20, row 6 = 10 (1 650 per screen); screen clear +350.

• Life lost: the ball's centre crosses y = 192 000 µu, the top of row 16.

gallery — shooter gallery

Walls on row 0, columns 0 and 16 and row 16; six bunker tiles on row 12 (each takes 3 hits); a 3-tile paddle on row 14.

• Avatar: fire spawns a friendly bolt (vy = -4 000 µu/tick) from the paddle centre, at most 2 in flight, with a 6-tick reload.
• Sprites: 32 marchers in a 4 × 8 formation on rows 2–5. The formation moves as one body: every marchTicks (screen 1: 20 ticks) it steps one tile horizontally, and when any marcher would leave columns 1…15 the whole body steps one tile down and reverses. marchTicks shortens per eight marchers destroyed, so a thinning formation accelerates. A live marcher fires a hostile bolt (vy = +2 600) when the per-tick draw is below fireChancePermille (18) and fewer than 3 hostile bolts are in flight; the firing marcher is the lowest live one in a drawn column.
• Saucer: 12/1000 per tick, never within 240 ticks of the last, crossing row 1 at 3 000 µu/tick. 100 points.
• Points: top marcher rank 30, then 20, 10, 10; saucer 100; wave clear +300.
• Life lost: a hostile bolt overlaps you, or any marcher reaches row 13 (which also resets the formation and restores the bunkers — a setback, not an instant game over).

The design note lists the eight formation columns as 1, 3, 5, 7, 9, 11, 13 and 15. That spread is flush against the note's own "would leave columns 1…15" bounds rule, so the body would step DOWN on every march tick and breach row 13 in 160 ticks — a wave nothing could clear. The eight columns shipped are adjacent and centred (5…12), which leaves four tiles of room to the left and three to the right: a drop every ~7 march steps, ~1 120 ticks to a breach, which is the pacing every other number in the note is sized for.

No tunnelling, proved rather than hoped

The fastest collidable is a gallery bolt at 4 000 µu/tick; the shallowest contact window is half a tile plus a box half-side, 6 000 + 3 000 = 9 000 µu. 9 000 > 4 000, so every collidable is overlapped for at least two consecutive end-of-tick positions in every legal configuration. tests/test_physics.nim asserts the inequality directly and cross-checks the swept test against the end-position test over 50 000 randomised states.

Scoring

scoreMicro[s] = 10 000 · points[s] + 1 000 000 · lives[s]
score[s]      = scoreMicro[s] / 1 000 000        (three decimals)

Placement is computed once at game over by this exact chain: higher score, then more lives left, then earlier lastScoreTick (reaching the same total sooner is better play), then lower seat index. The index tiebreak makes the chain total, so placements is always a strict permutation of 1…4 and exactly one seat wins. There are no shared places.

The league ranks by the seat's mean results.scores value across its episodes. results.rom records which cartridge an episode played, so a board can always be split per ROM afterwards.

Ending

A seat that never connects does not end the episode: the lobby timeout expires, the no-show is reported to COGAME_PLAYER_FAILURE_URI, its lane is driven by arcader for the whole run, and the round plays to a normal ending.

There is no rescue rule, no mercy and no difficulty reduction. A lane whose avatar never moves loses three lives and finishes near zero — a legible, correctly scored failure.