The Problem
Mateusz is a backend developer who writes Rust at work and wants to build a small arcade game for a game jam next weekend. He has 14 hours. He knows ownership and traits, but not game-engine structure: where the game loop lives, how to move things at a frame-rate-independent speed, how to keep menu and gameplay apart.
Bevy is the natural choice for a Rust developer, but it changes its API in nearly every release. Tutorials from two years ago use EventWriter, bundle structs and other names that no longer exist, and the code an AI assistant remembers is often from those versions. Each wrong guess costs a five-minute compile.
The Solution
The bevy skill pins the current release (0.20) and shows the forms that compile today: component tuples instead of bundles, Single for the one player entity, Message types for communication, States for menu and play. The rust skill covers the surrounding language and Cargo work, such as reading borrow-checker errors and setting up the dev profile. The agent checks every name against the tagged examples and docs.rs before using it.
Step-by-Step Walkthrough
Step 1: Create the project and pin the version
Create a new Rust project called dodge_game with Bevy 0.20 and the recommended dev profile for fast iteration. Check that it compiles.
rustup update stable
cargo new dodge_game
cd dodge_game
cargo add bevy@=0.20.0
The agent appends the officially recommended profile to Cargo.toml:
[profile.dev]
opt-level = 1
[profile.dev.package."*"]
opt-level = 3
cargo run --features bevy/dynamic_linking
The first build compiles the engine and takes a few minutes. A window opens. If the build stops on a missing alsa, udev or wayland library, the agent tells Mateusz which apt-get install line to run instead of running sudo itself.
Step 2: Spawn the player and the camera
Add a blue paddle at the bottom of the screen that moves with the arrow keys at 300 units per second.
The agent writes a Player component, a setup system that spawns Camera2d and a Sprite::from_color entity, and a move_player system that takes Single<&mut Transform, With<Player>>, reads ButtonInput<KeyCode> and multiplies by time.delta_secs(). It registers both with add_systems(Startup, setup) and add_systems(Update, move_player).
cargo run --features bevy/dynamic_linking
The paddle slides smoothly and moves at the same speed on Mateusz's 60 Hz laptop and on his 144 Hz monitor.
Step 3: Add falling hazards and a score
Every 0.8 seconds spawn a red block above the screen that falls at 200 units per second. Hitting the paddle resets the score, missing it adds one.
The agent adds a Hazard component, a repeating Timer kept in a Local, and a Score resource. The fall and hit system carries a Without<Player> filter on the hazard query, because the same system also reads the player's Transform and Bevy rejects overlapping queries. It despawns hazards with commands.entity(entity).despawn().
cargo check
The agent chains the three systems with .chain() so spawn, move and collision happen in a fixed order each frame.
Step 4: Split menu and play with states
Show nothing but a Menu state until Space is pressed, then switch to InGame. Game systems should only run in InGame.
The agent derives States on an AppState enum with #[default] Menu, calls init_state::<AppState>(), sets run_if(in_state(AppState::InGame)) on the gameplay systems, and adds a small system that calls next.set(AppState::InGame) when just_pressed(KeyCode::Space).
Step 5: Ship a release build
Build an optimised version I can send to the other jam team members.
cargo build --release
ls -lh target/release/dodge_game
The agent reminds Mateusz that the dynamic_linking feature must not be used for this build, and that the assets folder (none yet) would need to sit next to the executable.
Real-World Example
Mateusz had a playable loop in the first evening: a paddle, falling blocks, a score printed through info!, and a menu state. On the second day he added a high-score resource and a Message called PlayerHit that a sound system and a screen-shake system both read. When he upgraded from a pinned 0.19 to 0.20 on Sunday, cargo check listed 11 errors; the agent worked through them by category using the migration guide and the project compiled again in about 20 minutes. His team submitted a Linux release binary before the deadline.