Slime Dungeon

A cute 3D co-op dungeon crawler for 2–4 players, built on Colyseus 0.18 and three.js. Descend through procedurally generated floors, bonk slimes with your sword, and share one pool of hearts with the rest of the party.

npm start

Open http://localhost:5173 in two or more tabs (or browsers). Add ?mode=hard for fewer hearts and more, faster slimes; hard and normal parties never share a room.

• WASD / arrow keys: move. Space: swing (hold to keep swinging).
• Every slime that touches a hero costs the party one shared heart. At zero hearts the run restarts on a fresh dungeon.
• The stairs open once someone grabs the floor's key or the floor is cleared. Step on them to take the whole party down, and earn a heart back.
• Floors get bigger, with more and faster slimes. Blue ones appear on floor 2 and pink ones on floor 3, and a king slime guards the stairs on every third floor.

In development the client loads @colyseus/sdk/debug. The on-page panel shows per-reconciler drift (✓ matched / ~ jitter / ✗ diverging) and lets you tune interpolation. From the console, __net(150, 30) simulates 150 ms RTT ± 30 ms jitter, and __net() turns it off. Your own hero should still respond instantly, other heroes and slimes stay smooth, and swings still land on the slime you see.

Walking and swinging should keep the reconciler at 0 drift at any latency. Getting hit by a slime is the exception: the server shoves your hero, so you'll see one correction spike per hit. Persistent drift with nobody getting hit would mean the client and server steps have diverged.

• Fixed tick, buffered input. The room runs setFixedTimestep() at 30 Hz and consumes each client's inputs from defineInput(HeroInput), applying stepHero once per input. sanitize clamps the movement axes, because nothing off the wire is trusted.
• Only the seed is synced. The tile grid never crosses the wire: the state carries seed and floor, and generateDungeon() is a pure function of them. The predicted hero therefore collides against exactly the walls the server uses.
• Your hero is predicted. predict.reconciler() runs the same stepHero locally the moment an input is sent, then rolls back and replays unacknowledged inputs whenever a patch acknowledges one. Knockback from a slime is just a velocity on the hero that stepHero integrates, so a server-side shove replays cleanly. Hero positions are float64, so the reconciler adopts them bit for bit. t.number() would quietly drop to float32.
• Everyone else is interpolated. Other heroes and slimes render 100 ms in the past (mode: "lerp"). A snap threshold makes a floor change pop instead of gliding across the map.
• Sword hits are lag-compensated. Slime positions are recorded with allowRewindState(). When a swing starts, the server tests the arc against rewind.lastSeenBy(attacker), which is where that player's screen was drawing the slimes. The input's render-time stamp is bound to the same 100 ms interpolation delay, so the drawn position and the rewound one agree.
• Hits feel instant. The client also judges its own swing against the slimes as last drawn, and flashes them through predict.defineEvent(). The server's hp drop confirms the prediction; a hit nobody predicted (someone else's) plays when it arrives.

• src/app.config.ts: server configuration. Registers the dungeon room with filterBy(["mode"])
• src/rooms/DungeonRoom.ts: the authoritative game
• src/rooms/schema/DungeonState.ts: synchronized state and the input schema
• src/shared/: code both sides run (step, dungeon generator, combat, slime stats)
• src/client/: three.js renderer, HUD, controls, sound
• test/DungeonRoom.test.ts: boots the real server and connects real SDK clients
• test/shared.test.ts: determinism and generation checks for the shared code

• npm start: run Vite. Client and server share one port, with HMR
• npm test: run the mocha test suite
• npm run build: build the client (dist/client/) and the server (dist/server/)
• npm run loadtest: connect N simulated clients with @colyseus/loadtest

DungeonRoom.onDrop() holds a dropped player's seat for 30 seconds. Their hero stays in the dungeon, ghosted and ignored by slimes, while the SDK retries. onLeave() removes the hero only once they're gone for good.

• https://docs.colyseus.io/netcode
• https://docs.colyseus.io/room/reconnection