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shweet e9d8cac926 Weapons built from traits, fashion, Hourglass, About tab, and Ithaca

- Every attack is now assembled from traits on its definition instead
  of per-weapon code: an anchor and path (thrusts, out-and-back, arcs),
  shared flight physics (gravity, drag, acceleration, homing, and one
  wall response: end, burst, stick, crawl, bounce, stop, pass, return,
  latch), and flags like bouncy, drifting, tethered, orbiting, instant
  and arming. Melee are projectiles too.
- Shots have a lifetime and a fade (when damage bottoms out). Range is
  speed times lifetime. Ricochets and the Vacuum wind lifetime back.
- The Vacuum pulls anyone's shots, and its airblast flips them out
  along the aim, claiming enemies' (fading into your colour).
- New trinket: Hourglass, longer projectile lifetime and range. Ropes
  and chains lengthen with it and the Accelerator.
- Fashion: 23 items worn on the head, face or torso, chosen in Profile.
- Flamethrower flames hit continuously, the whip coils and sweeps,
  bouncing shots roll over ramps, and Ricochet relights grenade fuses.
- Profile tab, colour tooltips, option hints on every setting, an
  About tab with credits and links, and the Ithaca font.
- Loadouts lock once readied, tomatoes clear with the match, and the
  round-over pause is 4 seconds.
- CC0 license. Tools and CLAUDE.md are no longer tracked, and the web
  shell moves to web/.

2026-11-10 15:27:12 -05:00

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Smack a Brother

Online platform fighter. Lobbies of up to 16 players, games of up to 8. Play it in the browser here.

Clarification

This application was developed with the assistance of a large language model.

Build

After cloning and entering the repository's directory, make sure to initialize the submodules:

git submodule update --init --recursive

Everything (SDL, libdatachannel, simdjson) is built statically from the submodules. The game's resources are in resources/ and get linked next to the executable.

Linux

Needs OpenSSL, plus the X11/Wayland and audio headers SDL builds against.

mkdir build
cd build
cmake ..
make

Web

Needs the Emscripten SDK.

emcmake cmake -B build-web -DCMAKE_BUILD_TYPE=Release
cmake --build build-web

This makes smack-a-brother.html, .js, .wasm and .data. Rename the .html to index.html and serve all four.

Server

The server builds on its own, without SDL. It needs OpenSSL (libssl-dev on Debian).

cmake -S server -B build-server -DCMAKE_BUILD_TYPE=Release
cmake --build build-server

Run it with:

smack-a-brother-server [port] [first UDP port] [last UDP port]

Defaults are 47800, 47810 and 47899. It only listens on 127.0.0.1, so put it behind a reverse proxy that handles TLS. For nginx:

location /smack-a-brother/ws {
    proxy_pass http://127.0.0.1:47800;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_read_timeout 120s;
}

Open the UDP range in the firewall (e.g. ufw allow 47810:47899/udp).

Netcode

The server runs every lobby: a sandbox everyone in the lobby shares, plus the games queued in it. Each is its own simulation. All of them run on one thread, at 60 ticks a second.
Clients send their inputs ahead of time. Each tick the server takes what has arrived (repeating a player's last inputs if they're late), steps the simulation, and sends everyone the inputs it used. Every 60 ticks it also sends a checksum.
Clients run the same simulation about 3 ticks ahead of the server, guessing other players' inputs. When the server's inputs differ from the guess, the client rolls back and replays.
The simulation is deterministic on every platform (strict floating point, own maths functions), so desktop and web play together.
Clients connect over a WebSocket first (lobbies, chat, WebRTC signaling). Then they open a WebRTC connection to the server with two data channels: a reliable one, and an unreliable one for inputs and frames. If WebRTC can't connect, everything stays on the WebSocket.
STUN: stun.l.google.com:19302.
The server address is set in Settings. Default: wss://shweetz.net/smack-a-brother/ws.

Joining a lobby directly

Desktop: smack-a-brother --join CODE
Web: https://shweetz.net/smack-a-brother/?lobby=CODE

Environment variables

SAB_SERVER_URL: use a different server, e.g. ws://127.0.0.1:47800
SAB_NET_LAG: add this many milliseconds of lag
SAB_NET_LOSS: drop this percent of input packets
SAB_NET_STATS: log how the client is keeping up with the server

License

The game's code and art are released into the public domain under CC0 1.0. Not covered by that: the Ithaca font (SIL Open Font License, see resources/font/LICENSE.txt), the sound effects cut from the Sound Ideas libraries (see resources/sfx/SOURCES.md), and the libraries in external/, each under its own license.

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