This repository contains a basic multiplayer game inspired by Achtung, die Kurve!, written in Rust using Bevy Engine (v0.18) and Avian Physics. The goal of the project was to explore network programming when real-time movement is involved.

Features

• Implementation of Achtung, die Kurve! (also known as Curve Fever)
• Local multiplayer (up to 5 players)
• Online multiplayer (up to 5 players) over UDP using bevy_renet
• Touch controls for mobile devices
• Cross-platform (Linux, Windows, WebAssembly)

Note

Check out the branch with-bevy-renet for a P2P multiplayer implementation with renet which uses UDP. However, this version does not support WebAssembly multiplayer due to browser limitations around UDP.

Demo

Online multiplayer:

Menu:

Lobby with touch controls enabled:

In-game:

How to develop

Using Nix Flakes, JetBrains RustRover & Direnv

You can run this project in any way you like, but I have set things up to make it easy to develop using JetBrains RustRover. For this, you'll need:

• direnv
• Any Direnv integration plugin e.g. https://plugins.jetbrains.com/plugin/15285-direnv-integration
• nix

This way, you'll just need to direnv allow in the project directory after which all prerequisites (incl. Rust, Cargo, all Bevy dependencies, etc.) will be available to you. The JetBrains plugin will ensure that the environment is available to your IDE and you can run the project from there (vs cargo build and cargo run in the terminal).

How to deal with RustRover making problems again

RustRover will always fail to sync the project when you open it because it doesn't wait for direnv. Just re-sync immediately after the failure and it will work.

Did RustRover forget where the Rust standard library is again? Run the below and update the path in the settings:

find /nix/store -type d -name rust_lib_src

Using the Nix flake

Upgrade the flake by running nix flake update --flake . in the repository's base directory.

How to build WASM for the web

Warning

The web version does not support online multiplayer due to browser limitations around UDP.

Prerequisites

1. Run (already included in the Flake if using Nix):

   rustup target add wasm32-unknown-unknown

2. Set RUSTFLAGS environment variable:
   1. Linux:

      export RUSTFLAGS="--cfg=web_sys_unstable_apis --cfg=getrandom_backend=\"wasm_js\""

   2. Windows:

      $env:RUSTFLAGS="--cfg=web_sys_unstable_apis --cfg=getrandom_backend=`"wasm_js`""

3. Make sure you have Node.js with serve installed

Building

Then you can build the WASM file:

1. Build the WASM file:

   RUSTFLAGS='--cfg=web_sys_unstable_apis --cfg=getrandom_backend="wasm_js"' cargo build --target wasm32-unknown-unknown --release --no-default-features

2. Clean the /www/public directory and copy the game's assets over:
   • Linux:

     ./scripts/clean-mooplas-files.sh
     ./scripts/copy-assets.sh

   • Windows:

     ./scripts/clean-wasm-files.ps1
     ./scripts/copy-assets.ps1

3. Run wasm-bindgen to generate the JS bindings and move all relevant files to the /www/public directory:
   1. Linux:

      wasm-bindgen --out-dir ./www/public --target web ./target/wasm32-unknown-unknown/release/mooplas.wasm

   2. Windows:

      wasm-bindgen.exe --out-dir ./www/public --target web ./target/wasm32-unknown-unknown/release/mooplas.wasm

Optimising

You can optimise the WASM file (from the Unofficial Bevy Cheat Book):

# Optimize for size (z profile).
wasm-opt -Oz -o output.wasm input.wasm

# Optimize for size (s profile).
wasm-opt -Os -o output.wasm input.wasm

# Optimize for speed.
wasm-opt -O3 -o output.wasm input.wasm

# Optimize for both size and speed.
wasm-opt -O -ol 100 -s 100 -o output.wasm input.wasm

Running

Finally, to run the game in your browser locally, run the below and paste the URL copied to your clipboard into your browser:

npx serve ./www/public