# MAP.md — Barkour code index

Vanilla-JS canvas game, no build step. ES modules under `js/`, served statically.

- `index.html` — DOM shell: all screens (menu/host/join/charselect/game/result) as overlay divs; loads PeerJS from CDN (online play only), then `js/main.js`.
- `style.css` — overlay/menu styling; canvas letterboxed to 16:9 via CSS.
- `js/consts.js` — grid (TILE=12, 80×45 → 960×540), tile enum `T`, input bitmask `B`, item ids, physics constants, snapshot rate.
- `js/rng.js` — seeded mulberry32 (`makeRng`); `randomSeed()` is UI-side only.
- `js/mapgen.js` — side-view `generateMap(seed)`: ground heightmap, pits, towers, islands, one-way platforms, crystals (hp 3), pads, spikes, rail saws, spawns; `PALETTES`; `sawPos()` polyline eval (ping-pong or loop).
- `js/mapgen_arena.js` — top-down `generateArena(seed)`: mirrored (left↔right) walls/pits, corner spawns, guaranteed corridors spawn→center, fallback pit pair (pits are the only KO mechanic), mirrored saw pairs.
- `js/physics.js` — center-based AABB vs tile grid: `moveEntity` (per-axis, one-way platform aware), `raycast`, `boxFree`, `standingOnPlat`.
- `js/characters.js` — `CHARS` data (stats + visual params) and `updateCharacter()`: per-dog special movement (air dash / charge+pound / grapple constraint / blink / jetpack).
- `js/sim.js` — **authoritative, DOM-free side-view sim**: `createGame`, `step(game, inputs)` (60 Hz), combat (`hurt`: damage% → knockback), mining/items/hazards/KO/respawn/match-end, `snapshot`/`applySnapshot` for netplay. Sets `game.kind='side'`.
- `js/sim_arena.js` — top-down "Dogpit" sim, **same export surface as sim.js** (main.js swaps modules per match). x/y plane + z hop axis; KOs via pit falls; specials re-imagined per dog (dash cooldown, ram/slam, zip-leash, blink, hover). Sets `game.kind='arena'`.
- `js/input.js` — keyboard → bitmasks; slot 0 = WASD+FGH, slot 1 = arrows+KL;.
- `js/net.js` — PeerJS wrapper: `hostRoom`/`joinRoom`; room key = host peer id suffix; signaling via PeerJS cloud, game traffic pure P2P. Runs a 2s heartbeat + 8s watchdog (WebRTC close events are unreliable); broker `network` errors are ignored once the data channel is up.
- `js/render.js` — canvas: cached seeded background, tiles, procedural dog drawing, particles/ghosts driven by sim events (`fxEvents`), HUD, banners. Branches on `game.kind`: side view (`drawTiles`/`drawDog`) vs top-down (`drawTilesArena`/`drawDogTop`, z-height lifts the dog off its shadow).
- `js/audio.js` — WebAudio-synthesized sfx; `playEvents` maps sim events → sounds.
- `js/main.js` — app state machine: screens, char select (incl. mode toggle: `gameMode` 'side'|'arena', host-authoritative over the wire via `mode`/`start`/`rematch` messages), three match drivers (local / host / client) sharing one rAF fixed-timestep loop; `matchSim` points at the active sim module.
- `test/smoke.mjs` — `npm test`: headless mapgen determinism + chaotic full matches + targeted mining/stocks scenarios.

## Conventions & gotchas

- **Client never simulates.** In netplay the joiner only sends input bits and renders `applySnapshot` state; anything render reads must survive the snapshot round-trip (player `st` is re-shaped there).
- **Sim events are the only side-channel**: fx, audio, *and* client tile mutations (`tile`/`crack` events) ride on them. Host accumulates `pendingEvs` between snapshots.
- All sim/mapgen randomness must use the seeded RNG — never `Math.random()` inside `js/sim.js`/`js/mapgen.js`/`js/characters.js` paths.
- Velocities must stay < TILE (12 px/tick) or AABB collision tunnels.
- 7 as an arc end-angle in render means "> 2π" (full circle), a deliberate shorthand.