93 lines
3.4 KiB
Markdown
93 lines
3.4 KiB
Markdown
# Smack a Brother
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Online platform fighter. Lobbies of up to 16 players, games of up to 8. Play it in the browser [here](https://shweetz.net/smack-a-brother/).
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## Clarification
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This application was developed with the assistance of a large language model.
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## Build
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After cloning and entering the repository's directory, make sure to initialize the submodules:
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```git submodule update --init --recursive```
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Everything (SDL, libdatachannel, simdjson) is built statically from the submodules. The game's resources are in `resources/` and get linked next to the executable.
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### Linux
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Needs OpenSSL, plus the X11/Wayland and audio headers SDL builds against.
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```
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mkdir build
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cd build
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cmake ..
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make
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```
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### Web
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Needs the [Emscripten SDK](https://emscripten.org/docs/getting_started/downloads.html).
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```
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emcmake cmake -B build-web -DCMAKE_BUILD_TYPE=Release
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cmake --build build-web
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```
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This makes `smack-a-brother.html`, `.js`, `.wasm` and `.data`. Rename the `.html` to `index.html` and serve all four.
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### Server
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The server builds on its own, without SDL. It needs OpenSSL (`libssl-dev` on Debian).
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```
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cmake -S server -B build-server -DCMAKE_BUILD_TYPE=Release
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cmake --build build-server
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```
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Run it with:
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```smack-a-brother-server [port] [first UDP port] [last UDP port]```
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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:
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```
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location /smack-a-brother/ws {
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proxy_pass http://127.0.0.1:47800;
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proxy_http_version 1.1;
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proxy_set_header Upgrade $http_upgrade;
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proxy_set_header Connection "upgrade";
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proxy_set_header Host $host;
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proxy_read_timeout 120s;
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}
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```
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Open the UDP range in the firewall (e.g. `ufw allow 47810:47899/udp`).
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## Netcode
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- 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.
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- 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.
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- 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.
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- The simulation is deterministic on every platform (strict floating point, own maths functions), so desktop and web play together. `tools/determinism_check.sh` checks this.
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- 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.
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- STUN: `stun.l.google.com:19302`.
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- The server address is set in Settings. Default: `wss://shweetz.net/smack-a-brother/ws`.
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### Joining a lobby directly
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- Desktop: `smack-a-brother --join CODE`
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- Web: `https://shweetz.net/smack-a-brother/?lobby=CODE`
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### Environment variables
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- `SAB_SERVER_URL`: use a different server, e.g. `ws://127.0.0.1:47800`
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- `SAB_NET_LAG`: add this many milliseconds of lag
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- `SAB_NET_LOSS`: drop this percent of input packets
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- `SAB_NET_STATS`: log how the client is keeping up with the server
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