Your first project

The goal: a new Unreal project with a Rust actor that writes to the log when the game starts.

Creating the project

rusteal new MyGame --dir ~/Projects

rusteal new does everything a first build needs:

1. creates the Unreal project in ~/Projects/MyGame, from the engine’s Blank template;
2. installs the Rusteal plugins into its Plugins/;
3. writes the Rust workspace in Rust/, with your game crate and a HelloActor;
4. runs the whole build pipeline: it builds the project with the Unreal Build Tool, generates the Rust bindings for your engine, builds the game crate and deploys the library.

The first build takes a while: it compiles the engine module and generates bindings for the whole engine API. The builds after it only compile your crate.

rusteal new does not run git init, but it writes a .gitignore that covers Unreal’s and Cargo’s build output, so the right files are picked up when you do.

The Rust code

The game crate is in Rust/my-game/. Its src/lib.rs declares the library and its modules:

#![allow(unused)]
fn main() {
rusteal_runtime::entry!();

mod hello;
}

entry!() is required once per library: it is the function the Unreal plugin calls when it loads the library. Every other file is a normal Rust module.

src/hello.rs declares the actor:

#![allow(unused)]
fn main() {
use bindings::prelude::*;
use rusteal_runtime::{uclass, uclass_impl};

#[uclass(parent = Actor)]
pub struct HelloActor {}

#[uclass_impl]
impl HelloActor {
    #[ufunction(Override)]
    fn receive_begin_play(&mut self) {
        log::info!("[MyGame] Hello from Rust");
    }
}
}

• #[uclass(parent = Actor)] makes HelloActor an Unreal class whose parent is AActor.
• #[uclass_impl] marks the block where its Unreal functions are.
• #[ufunction(Override)] on receive_begin_play implements the engine’s ReceiveBeginPlay event, the one a Blueprint’s Event BeginPlay node implements.
• log::info! writes to the Output Log (see Logging).

In the editor

1. Open MyGame.uproject.
2. In the main menu, open Window > Place Actors.
3. In the Place Actors panel, type HelloActor in the search box.
4. Drag HelloActor from the panel into the level viewport.
5. Press Play in the toolbar.
6. Open the Output Log tab (Window > Output Log if it is not open).

The log shows:

LogRusteal: [MyGame] Hello from Rust

Screenshot: the Place Actors panel with HelloActor found by the search, and the Output Log showing the message. (images/getting_started/hello_actor.png)

Changing the code

Change the message in hello.rs, then build the crate again:

cd ~/Projects/MyGame
rusteal build

The editor reloads the library as soon as the build deploys it, without a restart, and shows a notification. Press Play again to see the new message. The iteration loop explains what a reload changes, and how rusteal watch builds on every save.

The flags of rusteal new