<div align="center">
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/logo.png" alt="Rusteal logo" width="256">
# Rusteal
[](https://crates.io/crates/rusteal)
[](https://github.com/viniciusmorgado/rusteal#license)
[](https://deps.rs/crate/rusteal)
</div>
---
**Rust bindings for Unreal Engine 5.8**
Rusteal lets you write Unreal Engine games and plugins in Rust: gameplay, reusable gameplay systems, editor tools. Your Rust code compiles to a shared library that is loaded by a small UE C++ plugin. All UE API calls cross the FFI boundary through a function pointer table — no C++ compilation required during Rust iteration.
> **⚠️ Early Stage Project** — Rusteal is under active development and **not ready for production use**. APIs will change without notice, documentation is incomplete, and many UE features are not yet covered. Contributions and feedback are welcome, but please do not use this for shipping projects.
---
## Why use Rusteal
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/mascot.png" alt="The Rusteal mascot" width="280" align="right">
**Use every core.**
The gameplay that weighs on a frame (AI for hundreds of
agents, simulations, pathfinding, procedural generation) spreads across every
core with `rayon` or threads of your own, and the compiler guarantees the
threads never race. The results reach Unreal's objects back on the game
thread, through `task::spawn`.
**Iterate in seconds.**
Your gameplay is a library of its own: Cargo rebuilds
your crate alone, without the Unreal Build Tool, and `Rusteal.Reload` swaps
the new code into the running editor.
**Test without the engine.**
Combat rules, inventories, economies and AI
written as plain Rust run under `cargo test`, with property tests and
benchmarks, without opening Unreal.
**Crash less.**
The borrow checker rules out use-after-free and data races in
your code, and a panic is caught at the FFI boundary and logged instead of
taking the editor down.
**Stay deterministic, share the rules.**
Fixed-point math and seeded random
numbers give the same simulation on every machine, the base of rollback and
lockstep netcode. The same rules crate can run in a dedicated Rust server, a
balancing tool or the web, with Unreal as the presentation.
**Bring the Rust ecosystem.**
crates.io is one line away: `serde` for saves
and configs, `rapier` for deterministic physics, `ggrs` for rollback,
`wasmtime` or `rhai` for sandboxed mods, `ort` for local inference.
**Feel at home on both sides.**
`#[uclass]`, `#[uproperty]` and
`#[ufunction]` speak Unreal's language, so anyone who knows the engine knows
where things go. Everything around them is Rust: structs and traits, `Result`
for errors, pattern matching, Cargo, rust-analyzer and clippy.
<br clear="right">
## Future migration to UE6
We are aware of the deep changes Unreal Engine 6 makes to the engine's
foundations: gameplay moving to Verse, Scene Graph replacing Actors and
Components, and Blueprints being deprecated once the new framework matures. We
follow them in Epic's own UE6 development stream (`ue6-main` in Epic's Unreal
Engine repository), and Rusteal's adaptation happens on the
[`ue6`](https://github.com/viniciusmorgado/rusteal/tree/ue6) branch, which
stays apart from `main` until UE6 ships.
So far, adapting Rusteal to UE6 looks feasible, with limited impact: Verse is
being built on the same UObject reflection and Unreal Header Tool that Rusteal
generates its bindings from. What changes, what Rusteal depends on and the open
questions are tracked in the
[UE6 radar](https://github.com/viniciusmorgado/rusteal/blob/ue6/docs/ue6-radar.md), on the `ue6` branch.
---
This README serves two different readers:
| **make a game** with Rusteal | [Making a game](#making-a-game) | the `rusteal` CLI from crates.io; not this repository |
| **make a plugin** (a gameplay system, an editor tool) with Rusteal | [Making a plugin](#making-a-plugin), after [Making a game](#making-a-game) | the `rusteal` CLI from crates.io; not this repository |
| **work on Rusteal itself** (its crates, CLI or UE plugins) | [Working on Rusteal](#working-on-rusteal) | a clone of this repository |
## Acknowledgments
Rusteal is a hard fork of [**uika**](https://github.com/VioletHelianthus/uika) by [**VioletHelianthus**](https://github.com/VioletHelianthus), who designed and wrote the foundation this project stands on: the reflection-driven code generator, the UHT exporter plugin, the reification of Rust structs as `UClass`es, and the runtime. Thank you.
Rusteal does not intend to stay compatible with the original uika, unless its author wants to port the improvements back. From here on it develops the Unreal bindings independently.
## Making a game
Everything from here to [Making a plugin](#making-a-plugin) is about using
Rusteal to write a game, and applies to a plugin's code as well. None of it
needs this repository.
### Prerequisites
The versions come from the engine's own requirements
(`Engine/Config/Windows/Windows_SDK.json` and `Engine/Config/Linux/Linux_SDK.json`
in UE 5.8.2) and from Rusteal's crates, which need Rust 1.88.
**Linux (x64)**
| A C toolchain | any | `build-essential` (Debian, Ubuntu), `gcc` (Fedora), `base-devel` (Arch) | the linker Rust uses (`cc`) |
| Rust | stable, 1.88 or newer | [rustup](https://rustup.rs) | installing the `rusteal` CLI, building your game crate |
| Unreal Engine | 5.8 | Epic's Linux build ([unrealengine.com/linux](https://www.unrealengine.com/linux)) or built from source | the game |
The engine brings the rest: the clang 20.1.8 toolchain UBT compiles with
(`v26_clang-20.1.8-rockylinux8`) and the .NET 10 SDK that runs UBT and UHT.
**Windows (x64)**
| Visual Studio IDE | Community, Professional or Enterprise; 2022 17.8 or newer, or 2026 18.0 or newer | [visualstudio.microsoft.com](https://visualstudio.microsoft.com) | the C++ compiler UBT uses, and the linker Rust uses |
| Rust | stable, 1.88 or newer, `x86_64-pc-windows-msvc` | [rustup](https://rustup.rs) (`rustup-init.exe`) | installing the `rusteal` CLI, building your game crate |
| Unreal Engine | 5.8 | the Epic Games Launcher | the game |
Any edition of the Visual Studio IDE works (Community is free). In the Visual
Studio Installer (**Modify** on an existing install), the **Workloads** tab needs
exactly two workloads:
| **Desktop development with C++** | Desktop & Mobile | MSVC, the C++ compiler and linker; the Windows SDK |
| **.NET desktop development** | Desktop & Mobile | the .NET Framework SDK (UBT stops with *Could not find NetFxSDK install dir* without it) |
**Game development with C++** and its Unreal Engine components are optional:
they add the IDE's Unreal integration, which the engine's command-line build,
the one Rusteal runs, does not use.
Then, in the **Individual components** tab, check that these are selected:
- **MSVC v143 x64/x86 build tools 14.44** for Visual Studio 2022, **MSVC
x64/x86 build tools 14.50** for 2026. The engine refuses 14.39 to 14.43,
14.44 before 14.44.35211 and 14.50 before 14.50.35723, and warns about
versions newer than these (the "latest" component of Visual Studio 2026
installs 14.51); with both installed, it picks the one it prefers;
- **Windows 11 SDK 10.0.22621** (10.0.19041 at least; UBT stops with
*Platform Win64 is not a valid platform to build* without one);
- **.NET Framework 4.6.2 targeting pack**.
Install Visual Studio before Rust: rustup uses its build tools for the MSVC
toolchain. The engine brings the .NET SDK for UBT and UHT.
Rust must use the MSVC host: `rustup show` prints *Default host:
x86_64-pc-windows-msvc*. If your default toolchain is a `-windows-gnu` one,
for another project, it can stay: set the default host
(`rustup set default-host x86_64-pc-windows-msvc`) and install
`stable-x86_64-pc-windows-msvc`, then pin it in your game project, either with
a `rust-toolchain.toml` or, for the directory holding your projects,
`rustup override set stable-x86_64-pc-windows-msvc --path <dir>`.
### Install
```bash
cargo install rusteal
```
That installs the `rusteal` binary; the engine plugins and the project
templates travel inside it. The first command that needs the engine asks where
it is and keeps the answer in `~/.config/rusteal/config.toml` — the only
per-machine setting Rusteal has.
Every command is also a Cargo subcommand: `cargo rusteal watch` is
`rusteal watch`, run from anywhere inside the project. An IDE that runs Cargo
commands (RustRover, VS Code's rust-analyzer tasks) can then start
`rusteal watch` or `rusteal build` with a Cargo run configuration whose command
is `rusteal watch`, the same on Linux and Windows.
### A new project
```bash
rusteal new MyGame --dir ~/Projects
```
`rusteal new` creates a UE project from one of the [templates](#templates),
`blank` unless `--template` names another, installs the Rusteal plugins, writes
the Rust workspace and runs the whole build pipeline. With `blank`, open
`MyGame.uproject`, drop a `HelloActor` into the level and press Play: the
Output Log shows `[MyGame] Hello from Rust`.
It does not run `git init` — versioning is your call — but it does write a
`.gitignore` covering the Unreal and Rust build output, so a later `git init`
picks up the right files.
Two flags: `--no-build` stops after writing the project, leaving the pipeline
for a later `rusteal build --all`; `--runtime-path` makes the project depend on a
Rusteal checkout instead of the published crates, which is for working on
Rusteal itself — see [Working on Rusteal](#working-on-rusteal).
### Templates
```bash
rusteal new MyGame --template third-person
rusteal new MyGame --template third-person --variant combat
```
A template is one of the engine's templates with its gameplay written in
Rust: the C++ classes are gone, the Rust crate in `Rust/` takes their place,
and their Blueprint children, with the same names, have Rust parents. The
engine's Blueprint-only templates (`vr`, `ar`, `intro`) keep their Blueprints too, reparented
to Rust classes and holding only data: meshes, materials, effects, input
assets, widget layouts and Anim Blueprint graphs.
The engine's templates come with variants, genre starting points the C++
version puts all in one project. Here each is its own project: `--variant`
picks one, and without it the project is the template alone (`base`). A
variant project is the template plus that variant, as the engine's Blueprint
templates make it, and opens and plays the variant's level.
| `blank` (default) | | The engine's Blank template and a `HelloActor` in Rust. |
| `first-person` | | The engine's First Person template: its character, camera manager, game mode and player controller in Rust, playable as it comes (keyboard, mouse, gamepad, touch). |
| `first-person` | `horror` | A dark level explored with a flashlight and a sprint that runs on stamina, its meter on screen. |
| `first-person` | `shooter` | An arena shooter: weapon pickups from a data table, projectiles and grenades, team scores, and NPCs run by a StateTree that sense, snipe and shoot. |
| `top-down` | | The engine's Top Down template: its character, game mode and point and click player controller in Rust (the engine's Blueprint-only base Blueprints made their children), playable as it comes (mouse, touch). |
| `top-down` | `strategy` | A real-time strategy start: units selected with clicks, boxes and touches, sent along the navigation mesh by EnvQueries, and interacting with the units they reach. |
| `top-down` | `twin-stick` | A twin stick shooter: projectiles, dashes and area attacks against waves of enemies run by a StateTree, pickups and a combo score. |
| `intro` | | The engine's Intro To Unreal template: its guided tour level, whose stations are the four [features](#features) below (copycat mannequins, checkpoints, triggers and doors, effects, animated keys, gizmos, editor hints), and its first person character, in Rust. |
| `third-person` | | The engine's Third Person template: its character, game mode and player controller in Rust, playable as it comes (keyboard, mouse, gamepad, touch). |
| `third-person` | `combat` | Melee combat: combo and charged attacks, enemies run by a StateTree, spawners, checkpoints, damageable props. |
| `third-person` | `platforming` | Double jump, wall jump, coyote time, a dash, local multiplayer and respawn. |
| `third-person` | `side-scrolling` | A side view platformer: soft platforms, jump pads, moving platforms, pickups with a counter and an NPC run by a StateTree. |
| `vehicle` | | The engine's Vehicle template: its sports car and offroad car on Chaos Vehicles, game mode, player controller and speed and gear HUD in Rust, playable as it comes (keyboard, gamepad, steering wheel, touch). |
| `vehicle` | `offroad` | The offroad car on an offroad level, its game mode ready for local split screen players. |
| `vehicle` | `time-trial` | A race track with a start countdown, gates to pass in order, laps and the best lap time. |
| `ar` | | The engine's Handheld AR template on ARCore and ARKit: its pawn (touch gestures to pick a detected plane, place the object on it, then move, rotate and scale it; light estimation), plane and placeable actors and its styled menus in Rust. It runs in the editor; Rusteal does not build for Android or iOS yet. |
| `vr` | | The engine's Virtual Reality template on OpenXR: its pawn (teleport along the navigation mesh, snap turn, hand poses), grabbable objects, pistol and projectiles, 3D menu, passthrough and spectator camera in Rust. |
Names are matched loosely (`side-scrolling`, `SideScrolling`), and `rusteal
new` with an unknown template or variant lists them all.
#### Features
A feature is gameplay any template can take: a Rusteal plugin with its Rust
classes, which `--feature` adds to the new project (as many as wanted).
```bash
rusteal new MyGame --template third-person --feature mannequin
```
| `mannequin` | `Mannequin` | `CopycatAnimInstance`, an Animation Blueprint parent that copies a character's movement (ground speed, direction, moving, falling), the player's unless told which, and `BP_CopycatMannequin`, the Intro To Unreal template's copycat mannequin; `ReachingMannequin`, whose right hand reaches for a `ReachTarget` placed in the level (two-bone IK solved in Rust). |
| `checkpoints` | `Checkpoints` | `BP_SpawnPoint`s that save the player's progress when walked past (`CheckpointSaveData`), and a world subsystem (`CheckpointSubsystem`) that brings the player back to the last one when the level starts or on `RespawnPlayer`. |
| `interactables` | `Interactables` | `BP_DoorTrigger`, a switch broadcasting its `Trigger` event; `BP_Light`s and a `BP_DoorFrame_Unlockable` that it toggles and unlocks; `BP_ConfettiTrigger`, a Niagara burst; `BP_SequenceTrigger`, which plays a level sequence; `BP_Metasound`, a MetaSound with a seed parameter; `BP_DangleBlocks`, cubes hanging on physics constraints. |
| `tour` | `Tour` | The tour pieces: `BP_TextSwitcher` (text that changes in game), `BP_Titles` (station numbers), animated `BP_KeyboardKey`s and `BP_MouseKey`s, `BP_GizmoDemo` (the move, rotate and scale gizmos at work), `BP_TemplateCube`, `BP_SplinePath` (decal arrows along a spline) and `BP_UI_Update` (editor panels shown in game). |
The `intro` template is made of all four: `rusteal new MyTour --template intro`
adds them by itself, and its level's Blueprints are children of their Rust
classes.
Each feature is written into `Plugins/<Plugin>/`, enabled in the `.uproject`,
built with the project, and brings the engine content it needs when the
project lacks it (`mannequin` copies the `Characters` pack, `interactables`
and `tour` the `LevelPrototyping` one). Its Blueprints are in the plugin's
content (**Plugins > <Plugin> Content** in the Content Browser), children of
its Rust classes holding the meshes, materials and widget layouts. An existing
project takes one with `rusteal plugin new <Plugin> --template <feature>`.
Other features add files to the project instead of a plugin: the setup of a
tool around it.
| `rustrover` | `Rust/.run/` | RustRover run configurations, stored as project files: **Rusteal Watch** (`cargo rusteal watch`) and **Rusteal Test** (`cargo test -p <game crate>`), the same on Linux and Windows. Open the project's `Rust` folder in RustRover to find them. |
### Screenshots
#### `first-person`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/first-person.png" alt="The first-person template in play" width="800">
#### `first-person` `horror`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/first-person-horror.png" alt="The first-person template's horror variant in play" width="800">
#### `first-person` `shooter`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/first-person-shooter.png" alt="The first-person template's shooter variant in play" width="800">
#### `top-down`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/topdown.png" alt="The top-down template in play" width="800">
#### `top-down` `strategy`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/topdown-strategy.png" alt="The top-down template's strategy variant in play" width="800">
#### `top-down` `twin-stick`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/topdown-twinstick.png" alt="The top-down template's twin-stick variant in play" width="800">
#### `third-person`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/third-person.png" alt="The third-person template in play" width="800">
#### `third-person` `combat`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/third-person-combat.png" alt="The third-person template's combat variant in play" width="800">
#### `third-person` `platforming`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/third-person-platforming.png" alt="The third-person template's platforming variant in play" width="800">
#### `third-person` `side-scrolling`
<img src="https://raw.githubusercontent.com/viniciusmorgado/rusteal/HEAD/assets/templates/third-person-sidescrolling.png" alt="The third-person template's side-scrolling variant in play" width="800">
### An existing project
```bash
rusteal setup /path/to/YourProject # plugins + starter rusteal.toml
rusteal build --all # from anywhere inside the project
```
`setup` does not write the Rust workspace; create it as below, or copy the
layout `rusteal new` produces.
### Versions
A project is tied to one Rusteal version: `Rust/Cargo.toml` pins
`rusteal-runtime`, `rusteal-core` and `rusteal-ffi` to it (`"=x.y.z"`), and the
plugins in `Plugins/` carry it. Before doing anything, `build`, `generate` and
`setup` check it against the CLI's own version (`rusteal --version`):
- the CLI is newer: `rusteal upgrade` moves the project to it — the pins, the
plugins (`Plugins/Rusteal` and `Plugins/RustealGenerator` are replaced
wholesale) and a full build;
- the project is newer: install the CLI it uses, `cargo install rusteal@x.y.z`.
The plugin checks the library as well: a `librusteal` built against another
version is refused at load, with both versions in the Output Log.
### Project layout
Everything lives in one repository; the only thing outside it is the engine path
in the CLI's own configuration.
```
YourProject/
├── YourProject.uproject
├── rusteal.toml # project configuration (versioned)
├── Source/YourProject/ # the C++ module UBT needs
├── Plugins/Rusteal/ # runtime plugin + generated C++ wrappers
├── Plugins/RustealGenerator/ # UHT exporter
├── Intermediate/Rusteal/uht/ # reflection JSON (build output)
└── Rust/
├── Cargo.toml # workspace
├── your-game/ # your code (cdylib)
└── bindings/ # generated by `rusteal build --all`, committed
```
**`Rust/Cargo.toml`** — `rusteal new` pins the version of the CLI that created
the project:
```toml
[workspace]
members = ["your-game", "bindings"]
resolver = "3"
[workspace.dependencies]
rusteal-runtime = "=x.y.z"
rusteal-core = "=x.y.z"
rusteal-ffi = "=x.y.z"
glam = "0.33"
```
**`Rust/your-game/Cargo.toml`:**
```toml
[lib]
crate-type = ["cdylib"]
[dependencies]
rusteal-runtime = { workspace = true }
bindings = { path = "../bindings" }
glam = { workspace = true }
```
**`Rust/your-game/src/lib.rs`:**
```rust
rusteal_runtime::entry!();
mod my_game;
```
The runtime types come from `rusteal_runtime::prelude`, the engine types from
the generated crate's own `bindings::prelude`.
## Build Pipeline
The CLI orchestrates a 5-step build. `rusteal build` runs steps 4 and 5, the
Rust libraries, which is all a change to Rust code needs; `rusteal build
--all` runs the five, which the first build of a project needs, and so does
every change to what the bindings are generated from: the engine version, or
the modules and the blocklist in `rusteal.toml`.
| 1 | UE Build | Compiles UE project, triggers RustealGenerator → JSON reflection data |
| 2 | Codegen | Reads JSON → generates the `bindings` crate + C++ wrappers |
| 3 | UE Rebuild | Compiles the generated C++ wrappers into the UE module |
| 4 | Cargo Build | `cargo build` of your cdylib crate, with the dev profile (`--release`: the release profile) |
| 5 | Deploy | Copies the library to `Plugins/Rusteal/Binaries/<Platform>/` (`rusteal.dll`, `librusteal.so`) |
Commands take the project directory, or find it by walking up from the current
one:
```bash
# The Rust libraries (steps 4-5), while you work on the game
rusteal build
# The same, every time a source file changes, until Ctrl+C
rusteal watch
# Every step
rusteal build --all
# Codegen and everything after
rusteal build --from 2
# Only one step
rusteal build --step 3
# Just regenerate the bindings crate and the C++ wrappers
rusteal generate /path/to/YourProject
# The game library for shipping
rusteal build --release
```
### Development and release builds
The game library is built with Cargo's dev profile by default, which is what
every build above does while you work on the game, and with the release
profile when `--release` is given, which is the build to ship. The two want
opposite things, and the templates set them up for that in the workspace's
`Rust/Cargo.toml`, the only place Cargo reads profiles from (in the game
crate's own `Cargo.toml` they are ignored with a warning):
- **dev** (iterating): recompiling after a change must be fast, and the game
must still run well in the editor. Only the game crate, the one that
changes, is barely optimized; the runtime crates and the generated
bindings, which compile once, are fully optimized. A change to the game
crate rebuilds in about a second. The game crate has full debug info; the
dependencies and the bindings keep only file and line, enough for
backtraces: with all of theirs, the library would be over a hundred
megabytes, which every hot reload loads again.
- **release** (shipping): the fastest library possible, however long it
takes to build. The whole program is optimized as one unit (link-time
optimization, a single codegen unit), which also drops the parts of the
bindings the game does not use.
The optimization levels follow Bevy's recommendations for game projects
([Bevy setup](https://bevy.org/learn/quick-start/getting-started/setup/));
trimming the dependencies' debug info is Rusteal's, for hot reload. The
Rusteal crates and the `rusteal` binary are not affected: these profiles only
shape the game's library.
## Key Concepts
### Object References
```rust
// Lightweight handle (8 bytes, Copy). May become invalid if UE GCs the object.
let actor: UObjectRef<Actor> = world.spawn_actor(&transform)?;
// RAII GC root. Prevents garbage collection until dropped.
let pinned: Pinned<Actor> = actor.pin()?;
// Checked access — verifies the object is still alive before use.
let checked = actor.checked()?;
checked.k2_get_actor_location();
// Upcast to any ancestor, checked at compile time (a Character is an Actor);
// downcast with `cast::<T>()`, checked at runtime.
let as_object: UObjectRef<Object> = actor.upcast_to::<Object>();
```
### Defining UE Classes
```rust
#[uclass(parent = Actor)]
pub struct MyActor {
#[component(root)]
root: SceneComponent,
#[component(attach = "root")]
mesh: StaticMeshComponent,
#[uproperty(BlueprintReadWrite, default = 100)]
health: i32,
// Assets and classes, assigned in a Blueprint child
#[uproperty(EditAnywhere)]
pickup_sound: UObjectRef<SoundBase>,
#[uproperty(EditAnywhere)]
projectile_class: SubclassOf<Actor>,
#[uproperty(EditAnywhere)]
materials: UeArray<UObjectRef<MaterialInterface>>,
// Rust-only field (not exposed to UE)
internal_state: Vec<String>,
}
#[uclass_impl]
impl MyActor {
#[ufunction(Override)]
fn receive_begin_play(&mut self) { /* ... */ }
#[ufunction(BlueprintCallable)]
fn take_damage(&mut self, amount: i32) {
self.set_health(self.health() - amount);
}
}
```
A `#[uproperty]` is `bool`, `i32`, `i64`, `u8`, `f32`, `f64`, an object
(`UObjectRef<T>`), a class (`SubclassOf<T>`, UE's `TSubclassOf<T>`), a
`UeArray` of any of those, of `FName`s or of structs (`UeArray<OwnedStruct<FLinearColor>>`), a struct (`OwnedStruct<FVector>`), an `FName`, a
`String` (`FString`) or an engine enum (`ECollisionChannel`). Each gets a
getter named after the field and a `set_` setter (`BlueprintReadOnly` is
about Blueprints; the class's own code writes it, as C++ does); an array's
getter returns a view of the array inside the object, changed in place, and
a struct's a copy. `default = ...` is for the scalar
types and enums; the others are set in `#[class_defaults]` or a Blueprint
child, as the engine's templates do. `EditAnywhere`, `EditDefaultsOnly`,
`VisibleAnywhere`, `BlueprintReadWrite`, `BlueprintReadOnly`, `SaveGame` and
`Config` are UE's specifiers; any other argument is a compile error. `Config`
reads and saves a property in the ini files of its class's config category
(`#[uclass(parent = ..., config = "Game")]`), as project settings do; see
[Project settings](#project-settings).
`SaveGame` is UE's flag for what a save writes: an archive that is a save
game archive (`ArIsSaveGame`, the usual way to save actors' state) serializes
only the properties that carry it. `GameplayStatics::save_game_to_slot` writes
a `SaveGame` object whole, flagged or not; marking its fields keeps them right
when it is serialized some other way. A save game class is a Rust class whose
parent is `SaveGame`:
```rust
#[uclass(parent = SaveGame)]
pub struct Progress {
#[uproperty(SaveGame)]
unlocked_difficulty: i32,
#[uproperty(SaveGame)]
best_times: UeArray<f32>,
}
let save = GameplayStatics::create_save_game_object(SubclassOf::<Progress>::base().upcast());
Progress::from_obj(save)?.set_unlocked_difficulty(2);
GameplayStatics::save_game_to_slot(save, "progress", 0);
let loaded = Progress::from_obj(GameplayStatics::load_game_from_slot("progress", 0))?;
```
A field with no attribute is Rust's alone, kept outside UE's object: its
getter returns a copy (a clone), `set_` replaces it, and `<field>_mut()`
changes it in place (a map, a vector).
The UE name is the field's in PascalCase, with a `b_` prefix as UE's bool
`b` (`b_force_touch_controls` is `bForceTouchControls`, as the bindings name
UE's own); `name = "NPC"` gives another, and `category = "..."` the property's
category. Matching the C++ names keeps the values a Blueprint saved when its
parent moves from C++ to Rust.
A `#[component]` is created with the object. `attach` names its parent: a
component the class declares before it, or an inherited one by its field-style
name (`root_component`, `mesh`); `socket` names a socket on that parent:
```rust
#[component(attach = "root_component")]
camera_boom: SpringArmComponent,
#[component(attach = "camera_boom", socket = "SpringEndpoint")]
follow_camera: CameraComponent,
```
A component's subobject is named after its field too, or as
`#[component(name = "Collision Check Box")]` says: a Blueprint child's
changes to an inherited component are kept by that name.
What a C++ constructor sets on inherited properties goes in a
`#[class_defaults]` method of the `#[uclass_impl]` block. It runs once, on the
class default object, which every instance and Blueprint child starts from:
```rust
#[class_defaults]
fn class_defaults(&mut self) -> RustealResult<()> {
let me = self.as_ref().checked()?;
me.set_use_controller_rotation_yaw(false);
me.get_character_movement().checked()?.set_max_walk_speed(500.0);
self.camera_boom()?.checked()?.set_target_arm_length(400.0);
Ok(())
}
```
A Rust class's parent may be a Rust class, as a C++ class's may be a C++
class: `#[uclass(parent = FirstPersonCharacter)]` makes a class with the
parent's properties, components and functions, whose components may attach to
the parent's by their field names (`attach = "first_person_camera_component"`)
and whose class defaults start from the parent's. An event both override runs
the child's code, which calls the parent's as C++ calls `Super::`:
```rust
#[ufunction(Override)]
fn receive_begin_play(&mut self) {
if let Ok(mut parent) = FirstPersonCharacter::from_obj(self.as_ref()) {
parent.receive_begin_play(); // pub(crate) in the parent's impl
}
// ...
}
```
In the generated bindings, an engine class reference (`TSubclassOf<T>`, such
as a game mode's `DefaultPawnClass`) is a `SubclassOf<T>`, not an object:
`get_default_pawn_class()` returns `SubclassOf<Pawn>`, and
`SubclassOf::<MyPawn>::base().upcast()` passes a Rust class where a parent's is
expected.
Static functions, such as a function library's (`UGameplayStatics`,
`UKismetSystemLibrary`), are called on the class, as in C++:
`GameplayStatics::get_player_controller(world, 0)`.
Private engine properties that Blueprint can read (`ACharacter`'s `Mesh`,
`CharacterMovement` and `CapsuleComponent`) have getters, and no setters when
they are read-only.
A `#[ufunction]` takes the scalar types, objects (`UObjectRef<T>`), classes
(`SubclassOf<T>`) and structs (`UStructRef<T>`, a reference into the call's
parameters; `to_owned()` keeps a copy), and returns a scalar, an object or a
class, or a `RustealResult` of one when it can fail (see [Errors](#errors)). It
is `BlueprintCallable` unless it says otherwise:
- `BlueprintPure`: callable without execution pins;
- `Override`: Rust code for an engine event of a parent class, taking what it
takes (an enum as its type or `u8`, an out struct as a `UStructRef` written
in place, a scalar out parameter as an `OutRef<T>`). A C++ virtual has its
event: `Landed` is `OnLanded`, `Tick` is `ReceiveTick`, `EndPlay` is
`ReceiveEndPlay`, `OnPossess` is `ReceivePossess`;
- `BlueprintImplementableEvent`: an event a Blueprint child implements; the
method's body is empty, and calling it runs the Blueprint's graph. It
takes structs as `&OwnedStruct<T>`;
- `Exec`, with the default or with `BlueprintPure`: a console command too,
see [Console commands and variables](#console-commands-and-variables).
`name = "K2_OnMovementModeChanged"` gives the UE name when the method's name
in PascalCase is not it. Any other argument is a compile error.
A class implements UE interfaces by class path: a C++ interface
(`/Script/Module.Interface`) or a Blueprint Interface asset
(`/Game/Path/BPI_Foo.BPI_Foo_C`). Its functions are `#[ufunction]`s named as
the interface's, taking the same parameters in the same order, and returning
its return value; C++'s `IFoo::Execute_Bar(Object)`, a Blueprint's interface
message and `DoesImplementInterface` reach them as they reach a Blueprint's.
```rust
#[uclass(parent = Actor, implements = ["/Game/Interaction/BPI_Usable.BPI_Usable_C"])]
pub struct Door {
#[uproperty(EditAnywhere)]
locked: bool,
}
#[uclass_impl]
impl Door {
/// BPI_Usable's Use(Instigator: Actor) -> bool
#[ufunction]
fn r#use(&mut self, instigator: UObjectRef<Actor>) -> bool {
!self.locked()
}
}
```
Interfaces load once the engine is initialized (a game module's or an
asset's cannot be loaded earlier), so the class implements them from then on.
An interface whose functions are not Blueprint events (marked
`CannotImplementInterfaceInBlueprint`) has only a C++ implementation and is
refused, as Blueprints refuse it. Between Rust classes, a Rust trait is the
lighter tool.
### Defining UE Structs
A data table's rows, or a struct a class's properties hold, can be declared in
Rust too, as UHT's `USTRUCT()`:
```rust
#[ustruct]
pub struct WeaponTableRow {
/// Mesh to display on the pickup
#[uproperty(EditAnywhere)]
static_mesh: SoftObjectRef<StaticMesh>,
/// Weapon class to grant on pickup
#[uproperty(EditAnywhere)]
weapon_to_spawn: SubclassOf<ShooterWeapon>,
}
```
Every field is a `#[uproperty]` of the kinds a class's are (no `default`: a
struct starts zeroed), since the struct's memory is UE's: a data table's, an
object property's, an `OwnedStruct`'s. The type itself is a marker, like the
bindings' engine structs, and the fields are read and written through the
generated `WeaponTableRowExt` trait on `UStructRef<WeaponTableRow>` and
`OwnedStruct<WeaponTableRow>`. A data table's row is found as C++'s
`FindRow<T>`, by the table and row name or by an `FDataTableRowHandle`:
```rust
let Some(row) = self.weapon_type().get_row::<WeaponTableRow>() else { return };
let mesh = row.static_mesh().load_synchronous()?;
self.set_weapon_class(row.weapon_to_spawn());
```
`SoftObjectRef<T>` is UE's `TSoftObjectPtr<T>`: an object by path, loaded on
demand (`load_synchronous`), or `get` if it already is.
### Defining UE Enums
An enum a Rust class's properties or functions use, and a Blueprint can pick
from a dropdown, is declared in Rust too, as UHT's `UENUM(BlueprintType)`:
```rust
#[uenum]
pub enum EGrabType {
None,
Snap,
Custom = 3,
Free,
}
#[uclass(parent = SceneComponent)]
pub struct GrabComponent {
#[uproperty(EditAnywhere, default = EGrabType::Free)]
grab_type: EGrabType,
}
```
A `#[uenum]` has unit variants with values up to 254, as a Blueprint enum's
`uint8`; the macro sets the representation. It is a property type, a
`#[ufunction]` parameter or return value, and a `match` like any Rust enum.
Engine enums from the bindings are ufunction parameters and return values too.
### Widgets
A Rust `UserWidget` reaches the widgets its Widget Blueprint's layout names as
C++'s `UPROPERTY(meta = (BindWidget))` does: a property with the widget's name
and `BindWidget` (`BindWidgetOptional` when the layout may leave it out) is
set when the widget is created. A widget animation of the Widget Blueprint is
reached the same way with `BindWidgetAnim` (`BindWidgetAnimOptional`), which
makes the property `Transient`, as the engine requires; `Transient` keeps any
property out of what is saved.
```rust
#[uclass(parent = UserWidget)]
pub struct MenuWidget {
#[uproperty(BindWidget, BlueprintReadOnly)]
restart_button: UObjectRef<Button>,
}
#[uclass_impl]
impl MenuWidget {
#[ufunction(Override)]
fn construct(&mut self) {
let me = self.as_ref().upcast_to::<UserWidget>();
if let Ok(button) = self.restart_button().checked() {
let _ = button.on_clicked().add_ufunction(&me, "Restart");
}
}
#[ufunction(BlueprintCallable)]
fn restart(&mut self) {
// ...
}
}
```
### Input
With the `enhanced-input` feature (on in new projects), input works as in the
engine's C++ templates: a Blueprint child assigns the input actions and mapping
contexts, the player controller adds the contexts, and the pawn binds the
actions to its functions once its input component exists, in
`receive_restarted` (C++ does it in `SetupPlayerInputComponent`):
```rust
use bindings::enhanced_input::{ETriggerEvent, FInputActionValue, InputAction};
use bindings::prelude::*; // bind_action, enhanced_input_subsystem, InputActionValueExt
#[uclass(parent = Character)]
pub struct MyCharacter {
#[uproperty(EditAnywhere)]
move_action: UObjectRef<InputAction>,
}
#[uclass_impl]
impl MyCharacter {
#[ufunction(Override)]
fn receive_restarted(&mut self) {
let me = self.as_ref();
let _ = bind_action(&me, self.move_action(), ETriggerEvent::Triggered, "Move");
}
#[ufunction(BlueprintCallable)]
fn r#move(&mut self, value: UStructRef<FInputActionValue>) {
let axis = value.axis2d(); // Value.Get<FVector2D>()
// ...
}
}
```
`bind_action` names the function by its UE name (`fn r#move` is `Move`), which
takes nothing, or the parameters of the engine's dynamic binding signature or
a leading part of them: the value, the seconds the action has been evaluated
and triggered, and the action itself. Engine functions work too (`"Jump"`).
```rust
#[ufunction]
fn charge(
&mut self,
value: UStructRef<FInputActionValue>,
elapsed_seconds: f32, // FInputActionInstance::GetElapsedTime()
triggered_seconds: f32, // GetTriggeredTime()
source_action: UObjectRef<InputAction>,
) {
// ...
}
```
`enhanced_input_subsystem(controller)` is where a player controller adds its
mapping contexts.
Touch controls follow the same template: `runtime::input::should_display_touch_interface()`
is the C++ `SVirtualJoystick::ShouldDisplayTouchInterface()` (a Slate check,
not in reflection), and `create_widget_of_class(&controller, class)` spawns a
widget whose class a Blueprint child assigns, as `CreateWidget<T>(this, Class)`
does.
### Delegates
An engine delegate (`OnActorBeginOverlap`, `OnDestroyed`, a component's
`OnComponentBeginOverlap`) takes a Rust closure, or a `#[ufunction]` by name
as C++'s `AddDynamic` does: once, however many times it is bound.
```rust
// A closure; dropping the binding unbinds it, detach() keeps it for as long
// as the actor lives.
actor.checked()?.on_destroyed().add(move |destroyed| { /* ... */ })?.detach();
// A #[ufunction] of this class taking the delegate's parameters.
me.checked()?.on_actor_begin_overlap().add_ufunction(&me, "BeginOverlap")?;
```
A Rust class declares its own multicast delegate with `#[udelegate]` in its
`#[uclass_impl]` block: C++'s `DECLARE_DYNAMIC_MULTICAST_DELEGATE` and a
`BlueprintAssignable` property, so Blueprints (a UMG widget showing the
health, say) bind it like any engine delegate. The method's body stays empty;
calling it broadcasts. Next to it come `<name>_add(closure)` and
`<name>_add_ufunction(target, "Function")` for Rust listeners.
```rust
#[uclass_impl]
impl PlayerCharacter {
/// Broadcast when health or armor change.
#[udelegate]
pub fn on_health_changed(&self, health: f32, armor: f32) {}
fn take_hit(&mut self, damage: f32) {
// ...
self.on_health_changed(self.health(), self.armor()); // broadcast
}
}
// elsewhere
character.on_health_changed_add(|health, armor| { /* ... */ })?.detach();
```
Its parameters are the scalar types, `#[uenum]`s, objects, classes and structs (as
`&OwnedStruct<T>`; a closure receives an `OwnedStruct<T>`). `#[udelegate(name =
"...")]` gives the UE name when the method's PascalCase is not it.
### Dynamic Calls
For Blueprint-defined functions or APIs not covered by generated bindings:
```rust
let mut call = DynamicCall::new(&actor, "SetMobility")?;
call.set("NewMobility", 2u8)?;
call.call()?;
```
### Errors
What fails in the engine (a destroyed object, a wrong cast, a missing
function) is a `RustealResult<T>`, whose `RustealError` says what went wrong,
on which object, why Unreal refused when it says, and where in your code:
```text
invalid cast: expected Pawn (object StaticMeshActor_0 of class StaticMeshActor)
at my-game/src/turret.rs:42:23
while aiming at the target
at my-game/src/turret.rs:30:14
```
```text
index out of range: Unreal: index 5 past the 0 elements of Items (ArrayProperty of Turret)
```
A `#[ufunction]` returns a `RustealResult<T>` when it can fail; Unreal sees it
return `T`. An `Err` is reported with the function's name and the function
returns the default value; called from a Blueprint, the error is a Blueprint
runtime error on the node that called it. Reported errors (and panics, with
their file and line) go to the Output Log with the Blueprint call stack, and
to the **Rusteal** tab of the Message Log (*Window > Message Log*), where the
object and the Rust line are links: the line opens in your IDE.
```rust
#[ufunction]
fn reload(&mut self) -> RustealResult<i32> {
let magazine = self.magazine().checked()?;
Ok(magazine.rounds())
}
```
`{e}` is one line, `{e:#}` adds the causes and the location, `{e:?}` is the
report above, and `e.log(LOG_WARNING)` writes it to the Output Log. The location
is the line of your call, since the functions returning a `RustealResult` pass
their caller's along. `.context("aiming at the target")` adds what the code was
doing, on any `Result` (another crate's error becomes the cause) and on an
`Option`; `?` converts the standard library's errors by itself. `kind()` is an
`ErrorKind` to match on (`e.is(ErrorKind::InvalidCast)`), and `bail!` and
`ensure!` return errors of your own. `RustealError` implements
`std::error::Error`, so it also goes into `anyhow` or an error type of yours.
### Hot Reload
During development, rebuild your Rust library and reload without restarting the editor:
```bash
rusteal build
```
The editor reloads each library as soon as `rusteal build` deploys it again,
with a notification (`Rusteal.AutoReload 0` in the console turns that off).
`rusteal watch` runs that build every time you save a Rust file, so saving is
all it takes; a build that fails prints its errors and the watch goes on
(`--plugin <Name>` watches one plugin). To reload by hand, in the UE console:
```
Rusteal.Reload
```
`Rusteal.Reload` swaps every Rust library of the project; `Rusteal.Reload
<Name>` only one (the game's is named after the project, a plugin's after the
plugin). Function bodies update immediately. A class whose `#[uproperty]`s,
`#[component]`s, `#[ufunction]`s or parent changed is created again, and its
objects move to the new class: the actors in the level, its Blueprint
children and its Rust subclasses, keeping their property values. Rust-private
fields start over on every reload. A changed `#[ustruct]` still needs an editor
restart, and so does a changed class outside the editor (`-game`). How it
works, and why: [docs/hot-reload.md](docs/hot-reload.md).
#### Console commands
Typed in the editor's console: the `` ` `` key in the viewport, or the **Cmd**
box at the bottom of the **Output Log** tab.
| `Rusteal.Reload` | Reloads every Rust library of the project. |
| `Rusteal.Reload <Name>` | Reloads one library: the game's is named after the project, a plugin's after the plugin. |
| `Rusteal.AutoReload 0` | Stops reloading a library when `rusteal build` deploys it again; `Rusteal.Reload` still works. |
| `Rusteal.AutoReload 1` | Reloads a library when it is deployed again, the default. |
### Packaging a game
```bash
rusteal package # Development, into <project>/Packaged
rusteal package --shipping --output ~/Builds/MyGame
```
`rusteal package` builds every library with the release profile, then cooks
and packages the game for the platform it runs on (the engine's
`BuildCookRun`). The packaged game stages each Rust library it loads, the
game's and its runtime plugins'. Assets that only Rust code loads by path
(`load_object`) are not found by the cooker through references: list their
directory in *Project Settings > Packaging > Additional Asset Directories to
Cook*.
### Platform optimizations
Some engine settings only make sense on one platform. `rusteal.toml` lists them
per platform (`linux`, `windows`, `mac`), as
`[optimizations.<platform>.<File>.<Section>]`, and the CLI writes the table of
the platform it was compiled for into the project's
`Config/<Platform>/<Platform><File>.ini`, between two Rusteal comment lines:
```toml
[optimizations.linux.Engine.ConsoleVariables]
"r.Vulkan.CpuWaitForFence" = 0
```
```ini
; Rusteal optimizations, written by rusteal from rusteal.toml [optimizations]: begin
[ConsoleVariables]
r.Vulkan.CpuWaitForFence=0
; Rusteal optimizations: end
```
Every template ships this Linux setting: the swapchain image is waited on with
a GPU semaphore instead of a CPU fence, because NVIDIA's Linux driver crashes
in `vkWaitForFences` after the swapchain goes out of date (resizing, closing a
window, stopping PIE). Epic ships the same value on Android.
| `rusteal new` | Writes them into the new project. |
| `rusteal watch` | Writes them when it starts, so every machine a developer works on gets them. |
| `rusteal package` | Writes them for the packaged game, then puts the project's files back as they were. |
| `--optimizations off` (or `0`) | On any of the three: leaves them out (`watch`: removes them until the next `watch`). |
- A key you already set yourself in that `.ini`, outside the Rusteal lines,
keeps your value; the rest of the file is never touched.
- A Windows CLI never writes Linux settings, and a Windows package never
carries them (the engine stages `Config/Linux` only for Linux).
- A project whose `rusteal.toml` has no `[optimizations]` table gets the
defaults above; an empty `[optimizations]` turns them all off.
- Settings changed in the engine install itself, such as
`Engine/Config/Linux/LinuxEngine.ini`, apply to every project and every
game packaged with that engine, whatever `--optimizations` says, and are
lost when the engine is reinstalled or upgraded.
## Making a plugin
Rusteal makes Unreal Engine plugins too: a plugin whose code is a Rust
library of its own, loaded next to the game's. A gameplay system written once
(an inventory, dialogue, quests, AI) goes into any project as a plugin, and an
editor tool brings what Rust does well into the editor: work on many assets at
once, parsers and other libraries from crates.io, all of it off the game
thread when it is heavy.
A plugin's library is either kind:
| `runtime` | games and the editor | `Runtime` | gameplay systems, anything a packaged game needs |
| `editor` | the editor only | `Editor` | tools: menus, asset validation, editor scripting |
Everything in [Making a game](#making-a-game) applies to a plugin's code: its
classes, properties, functions, components, delegates and interfaces are
written the same way.
### A new plugin
A plugin lives in a Rusteal project, which builds it with the engine and gives
it a level to be tried in: the game it is for, or a project made for it.
```bash
rusteal new PluginLab # any Rusteal project works
cd PluginLab
rusteal plugin new Inventory # Plugins/Inventory/, built
rusteal plugin new LevelTools --template editor # an editor plugin
```
`rusteal plugin new` writes the plugin into the project's `Plugins/`, lists it
in the `.uproject` and runs the build pipeline. The plugin's name is also its
C++ module's: letters and digits, not the project's own name.
| `blank` (default) | A runtime plugin with a `HelloComponent` in Rust. |
| `editor` | An editor plugin: an editor subsystem, a *Tools* menu entry counting the project's assets on a background thread, a console command doing the same, and an asset validator. |
| `inventory` | A runtime gameplay plugin: items as data assets (`<Name>Item`), an inventory component stacking them and broadcasting its changes (`<Name>Component`), a world subsystem (`<Name>Subsystem`), project settings for its limits (`<Name>Settings`) and console commands giving, taking and listing the player's items. |
| `mannequin` | The `mannequin` feature (see [Features](#features)). |
### Plugin layout
```
Plugins/Inventory/
├── Inventory.uplugin # the plugin, depending on Rusteal
├── rusteal.toml # the plugin's library: crate, kind, modules
├── Source/Inventory/ # its C++ module, which hands the library to Rusteal
│ └── Generated/ # generated C++ wrappers (versioned)
├── Rust/
│ ├── Cargo.toml # the plugin's own workspace
│ ├── inventory/ # its code (cdylib)
│ └── bindings/ # generated by `rusteal build --all`, committed
├── Binaries/<Platform>/ # librusteal_Inventory.so, rusteal_Inventory.dll
└── Content/ # the plugin's assets
```
The plugin carries everything it needs, so the directory can be copied into
another Rusteal project at the same version, or kept in a repository of its
own. Its `Rust/Cargo.toml` pins the Rusteal crates as the project's does, and
`rusteal upgrade` moves both.
A plugin's classes live in its module's package, as a C++ plugin's do:
`/Script/Inventory.InventoryComponent`, where the game's are in
`/Script/Rusteal`. That is their path in assets, ini sections and editor
Python (`unreal.load_class(None, "/Script/Inventory.InventoryItem")`).
### Building
`rusteal build` builds every library of the project: the game's and each
plugin's. `--plugin <Name>` limits the codegen, Cargo and deploy steps to one
plugin, which is what iterating on it needs:
```bash
rusteal build --plugin Inventory
```
In the editor, `Rusteal.Reload` swaps every library, `Rusteal.Reload
Inventory` only that one.
A plugin binds the engine modules its `rusteal.toml` lists, like a game. A
module far bigger than a plugin needs can be limited to some classes (and the
ones they derive from):
```toml
UnrealEd = { module = "unreal_ed", feature = "editor", classes = ["EditorActorSubsystem", "EditorAssetSubsystem"] }
```
### Subsystems
A subsystem is where a plugin's system usually lives: the engine makes one for
every class deriving from a subsystem base, with the lifetime of the game, a
world, the engine or a local player. A Rust class derives from Rusteal's
parents, which turn the engine's C++ virtuals into events:
| `RustealGameInstanceSubsystem` | game | `receive_initialize`, `receive_deinitialize`, `receive_should_create_subsystem` |
| `RustealWorldSubsystem` | world (game and PIE; editor worlds with `bCreateInEditorWorlds`) | the same, `receive_post_initialize`, `receive_world_begin_play`, `receive_tick` with `bWantsTick` |
| `RustealEngineSubsystem` | process | the same as the game's |
| `RustealLocalPlayerSubsystem` | local player | the same, `receive_player_controller_changed` |
| `RustealEditorSubsystem` (editor libraries) | editor | the same as the game's |
```rust
#[uclass(parent = RustealWorldSubsystem)]
pub struct Waves {}
#[uclass_impl]
impl Waves {
#[class_defaults]
fn class_defaults(&mut self) -> RustealResult<()> {
self.as_ref().checked()?.set_wants_tick(true);
Ok(())
}
#[ufunction(Override)]
fn receive_world_begin_play(&mut self) { /* ... */ }
#[ufunction(Override)]
fn receive_tick(&mut self, delta_seconds: f32) { /* ... */ }
}
```
Other code finds it as it finds any subsystem:
`SubsystemBlueprintLibrary::get_world_subsystem(context, class)`.
### Project settings
A class whose parent is `DeveloperSettings` and that names a config category
shows in *Project Settings*, its `Config` properties saved in that category's
files (`config = "Game"`: `Config/DefaultGame.ini`):
```rust
#[uclass(parent = DeveloperSettings, config = "Game")]
pub struct InventorySettings {
#[uproperty(Config, EditAnywhere, category = "Inventory", default = 20)]
max_slots: i32,
}
let slots = InventorySettings::get_default()?.max_slots();
```
The plugin templates bind the `DeveloperSettings` module; a game adds it to
its `rusteal.toml` (`DeveloperSettings = { module = "developer_settings",
feature = "engine" }` in `[codegen.modules]`). `get_default()` is the class
default object, which holds the settings: the defaults, overridden by what
the ini files hold, under the class's path and the properties' UE names:
```ini
[/Script/Inventory.InventorySettings]
MaxSlots=30
```
### Console commands and variables
```rust
use rusteal_runtime::runtime::console;
pub const GOD_MODE: ConsoleVariable<bool> = ConsoleVariable::new("inventory.infinite");
fn startup() {
let _ = GOD_MODE.register("Items are never used up", false);
let _ = console::register_command("inventory.give", "inventory.give <item> [count]", |args, world| {
// args: ["sword", "2"]; world: the world the command runs in
});
}
rusteal_runtime::on_load!(startup);
```
`on_load!` runs a function each time the library loads, hot reloads included:
an unload removes the library's commands and variables, and the next load
registers them again. A `ConsoleVariable<T>` (`bool`, `i32`, `f32`,
`String`) reads and writes any variable by name, the engine's too
(`ConsoleVariable::<i32>::new("t.MaxFPS").set(60)`).
A `#[ufunction(Exec)]` is a console command on the classes the console reaches,
as `UFUNCTION(Exec)` is in C++: the player controller, its pawn and HUD, the
cheat manager, the game mode and the game state. The command is the function's
UE name: `fn give_gold(&mut self, amount: i32)` is `GiveGold 100`.
### Work off the game thread
UE's objects belong to the game thread; Rust's threads, `rayon` and `tokio`
are free to do the rest. `task::spawn` runs the work on a thread of its own
and hands its result back on the game thread, where UE can be called again:
```rust
use rusteal_runtime::runtime::task;
task::spawn(
move || index_assets(&paths), // a background thread: no UE calls
move |index| apply_index(index), // the game thread, a frame later
);
task::run_on_game_thread(|| { /* from any thread */ });
```bash
rusteal plugin package Inventory --output ~/Packages
```
builds the plugin's library with the release profile and copies the plugin
into `~/Packages/Inventory`: its sources (the C++ module, the Rust crate, the
generated code), content and configuration, its binaries for the platform it
was built on (the Rust library, the editor module), and none of the build
output. Another Rusteal project at the same version takes it into its
`Plugins/` and builds it with `rusteal build --all`; a binary for another platform
comes from packaging there. A game packaged with [`rusteal
package`](#packaging-a-game) stages the libraries of its runtime plugins with
its own.
### What a plugin cannot do yet
Slate UI, details panel customizations, custom asset editors, scripted asset
actions, importers and Blueprint nodes are not covered yet; what they take, and
what to do meanwhile, is in
[`docs/plugin-roadmap.md`](https://github.com/viniciusmorgado/rusteal/blob/main/docs/plugin-roadmap.md).
## Platform Support
| Linux (x64) | Supported (Unreal Engine 5.8.2) |
| Windows (x64) | Supported |
| macOS | Not yet tested |
## Known limitations
- **Mobile.** Rusteal does not build for Android or iOS yet. The `ar`
template, made for ARCore and ARKit devices, runs in the editor, and the
touch controls of the other templates can be tried there, but none of them
can be packaged for a phone or a tablet. Mobile support is being actively
worked on.
- **Consoles.** Rusteal does not build for consoles yet; console support is
being actively worked on too.
## Working on Rusteal
This part is for changing Rusteal itself: its crates, the `rusteal` CLI and the
UE plugins in `ue_plugin/`. To make a game, none of it is needed; see
[Making a game](#making-a-game).
### Prerequisites
Everything in [Making a game › Prerequisites](#prerequisites), plus:
| Git | the distribution's package (`git`); on Windows, [Git for Windows](https://git-scm.com/download/win) | cloning the repository |
| [clangd](https://clangd.llvm.org) (optional) | the distribution's package or LLVM; Zed downloads it on its own | C++ support in the editor, for `ue_plugin/` |
| [.NET 10 SDK](https://dotnet.microsoft.com/download) (optional) | Microsoft, or the distribution's package (`dotnet-sdk-10.0`) | C# support in the editor, for the exporter in `ue_plugin/RustealGenerator/` |
The checkout builds with the MSRV, Rust 1.88.0, whatever your default
toolchain is: `rust-toolchain.toml` pins it, and rustup installs it on the
first `cargo` command. The file names no host, so rustup completes it with its
default host; on Windows that must be `x86_64-pc-windows-msvc` (see the
Windows prerequisites above).
### Development environment
The settings that depend on the machine live in `.env` at the repository root,
which is not versioned; `.env.example` lists them:
| `RUSTEAL_DEV_ENGINE_ROOT` | The Unreal Engine root, the directory holding `Engine/` |
Linux:
```bash
git clone https://github.com/viniciusmorgado/rusteal.git
cd rusteal
cp .env.example .env # then fill it in
cargo xtask dev-setup
```
Windows (PowerShell):
```powershell
git clone https://github.com/viniciusmorgado/rusteal.git
cd rusteal
Copy-Item .env.example .env # then fill it in
cargo xtask dev-setup
```
Rusteal is developed against a UE project: the plugins in `ue_plugin/` are built
inside one, and the C++ editor support reads what that build generates (UHT's
`*.generated.h` headers and UBT's compile commands). `dev-setup` asks which one:
1. **An existing project.** It must have this checkout's plugins installed and
built (`cargo run -p rusteal -- setup <project>`, then `build`); `dev-setup`
only reads it, never changes it, and stops with those commands if they are
missing. Plugin headers that differ from the checkout's are reported.
2. **A new blank project**, created at the path you give with
`rusteal new --runtime-path` on this checkout, and built. The last component
of the path is the project name.
To skip the question, pass the answer: `cargo xtask dev-setup --project <path>`
or `cargo xtask dev-setup --new <path>`.
Then it writes:
- **`compile_commands.json`** at the repository root, for clangd: the compile
commands UBT gives for that project, pointed at `ue_plugin/`;
- **the exporter's `.csproj.props`**, so C# language servers resolve the
engine's `EpicGames.*` assemblies, and a `dotnet restore` of `rusteal.sln`
with the .NET SDK bundled with the engine. The solution has two projects, both
for IDEs only: the exporter (`ue_plugin/RustealGenerator/Source/RustealExporter/`),
and `ide/RustealRules/`, which gives the plugins' `*.Build.cs` files the context
UBT compiles them with. Without that project a language server analyzes those
files with no references at all: nothing resolves, and every `using` is
reported as unnecessary. UBT compiles the `Build.cs` files without implicit
usings, so a `using System.IO;` there is required, and the project makes the
editor agree.
Run it again after adding a source file to the plugin, or after changing a
header that declares a `UCLASS` or `USTRUCT` and rebuilding it in the project:
a generated header only matches the header it was made from.
`.env` is for working on Rusteal only:
| Engine path from | `.env` | the `rusteal` CLI, which asks once and keeps it in `~/.config/rusteal/config.toml` (the platform's config directory elsewhere) |
| Read by | `cargo xtask` only | the `rusteal` CLI |
| Writes the exporter's `.csproj.props` | `cargo xtask dev-setup`, in this checkout | `rusteal setup`, in the game project |
The `rusteal` CLI never reads `.env`, so it does not change which engine a game
builds with.
### Testing a change
The workspace builds, tests and lints without the engine:
```bash
cargo build --workspace
cargo test --workspace
cargo clippy --workspace --no-deps
```
Anything that touches the engine is tested in a UE project of your choice,
driven by this checkout's CLI (`cargo run -p rusteal --`, from the repository
root). A new project that depends on this checkout:
```bash
cargo run -p rusteal -- new Probe --dir /tmp --runtime-path .
```
After changing the runtime, the macros or a game crate:
```bash
cargo run -p rusteal -- build /tmp/Probe
```
After changing the UE plugins in `ue_plugin/`, reinstall them into the project
and build it:
```bash
cargo run -p rusteal -- setup /tmp/Probe
cargo run -p rusteal -- build /tmp/Probe --all
```
In the editor, each `build` reloads the library by itself, changed classes
included (see [Hot Reload](#hot-reload)); a change to the UE plugins needs an
editor restart.
A project made with `--runtime-path` follows that checkout: the CLI acts on it
only when built from the same checkout, so drive it with `cargo run -p rusteal --`
from there. After pulling, `setup` reinstalls the plugins at the checkout's
version.
### `--runtime-path`
It decides where the generated project takes Rusteal from:
| `Rust/Cargo.toml` says | `rusteal-runtime = "=x.y.z"` | `{ path = "<checkout>/rusteal-runtime" }` |
| Crates come from | crates.io | the local checkout |
| A change in the runtime reaches the game | on the next published version | on the next build |
| The project builds on another machine | yes | no (the path is this machine's) |
So: without it for a real game, with it while working on Rusteal — a change in
`rusteal-core` shows up in the project you test with on the next `build`,
with nothing to publish in between.
### What lives where
| `rusteal-ue-flags` | UE reflection flag constants |
| `rusteal-ffi` | `#[repr(C)]` types and the API table: the Rust ↔ C++ contract |
| `rusteal-core` | the safe runtime: object references, lifecycle, containers, math |
| `rusteal-macros` | `#[uclass]`, `#[uclass_impl]` and their attributes |
| `rusteal-runtime` | what a game depends on; re-exports the above |
| `rusteal-codegen` | reflection JSON → the `bindings` crate and the C++ wrappers; owns `manual/` |
| `rusteal-cli` | the `rusteal` binary; owns `templates/` and `plugin_templates/`, and embeds `ue_plugin/` |
Changing the C++ plugin means running `cargo run -p rusteal -- sync-plugin`
before publishing, which refreshes the snapshot the binary embeds.
### Adding a template
A template is a directory under `rusteal-cli/templates/`, one directory per
variant inside it, `base` being the template without `--variant`; they are
embedded in the binary when it is built, and nothing else registers them. A
variant directory mirrors the root of the project it creates:
- `template.toml` names the engine template the project starts from
(`engine_template`), the paths of it to leave out (`exclude`: the C++
gameplay the template replaces, the other variants), the level to open
when it is not the engine template's own (`default_map`), a one-line
`description` and the `next_step` printed at the end;
- every other file is written into the project over the engine template's:
`*.tera` files are rendered with [Tera](https://keats.github.io/tera/) and
lose the extension, the rest (Blueprints, meshes) is copied as is;
- `{{ variable }}` works in folder and file names too:
`Rust/{{crate_name}}/src/lib.rs.tera`.
The context is the same for every template: `project`, `crate_name`,
`version`, `glam_version` and, with `--runtime-path`, `runtime_path`.
Each variant is complete on its own. A new one starts as a copy of the
closest existing one (a variant from its template's `base`) and is changed
from there, never layered on top of it. Its Blueprints come from a project
where they were made and played, saved with the engine version Rusteal
targets. A variant with something to see has a screenshot in
`assets/templates/`, shown in [Screenshots](#screenshots).
A plugin template is a directory under `rusteal-cli/plugin_templates/`,
written into `Plugins/<Name>/` by `rusteal plugin new --template <name>`:
its `template.toml` has the `description` and the `next_step`, and its files
are rendered the same way, with `plugin`, `crate_name`, `version`,
`glam_version` and `runtime_path` as context. The plugin's module, its
`Build.cs` and `<Name>Module.cpp`, come with the template: copy them from
`blank` (a runtime module) or `editor` (an editor module).
A plugin template with a `[feature]` table in its `template.toml` is a
feature: `plugin` is the plugin's name in the project (its assets live under
`/<plugin>/`, so a feature with `Content/` keeps that name), and
`shared_packs` lists the engine template packs it needs
(`High/Characters` is `Templates/TemplateResources/High/Characters`), copied
into the project's `Content/` without replacing what is there. A template's
`template.toml` bundles features with `features = [...]`.
Engine APIs Rusteal uses that Unreal has deprecated are tracked in
[`docs/ue-deprecations.md`](https://github.com/viniciusmorgado/rusteal/blob/main/docs/ue-deprecations.md): what, since which UE
version, until when and where. A new engine version means checking its
warnings against that list.
What Rusteal still lacks to write Unreal's Third Person template entirely in
Rust, in the order the template needs it, is mapped in
[`docs/third-person-gaps.md`](https://github.com/viniciusmorgado/rusteal/blob/main/docs/third-person-gaps.md).
How the engine templates' variants were ported, where the Rust ports differ
from the C++ and what they still work around is in
[`docs/template-variants.md`](https://github.com/viniciusmorgado/rusteal/blob/main/docs/template-variants.md).
What Rusteal does not do yet for plugins (Slate, details customizations,
importers, Blueprint nodes...), and what each takes, is in
[`docs/plugin-roadmap.md`](https://github.com/viniciusmorgado/rusteal/blob/main/docs/plugin-roadmap.md).
What Unreal Engine 6 changes for Rusteal — Verse, Scene Graph, the end of
Blueprints — and the open questions to check as Epic publishes details are in
the [UE6 radar](https://github.com/viniciusmorgado/rusteal/blob/ue6/docs/ue6-radar.md), kept on the `ue6` branch (see
[Future migration to UE6](#future-migration-to-ue6)).
Commits are small — one per fix.
### Releases and versions
Everything Rusteal ships carries one version: the seven crates (they inherit
`[workspace.package].version` through `version.workspace = true`), the two UE
plugins and the FFI contract between them.
**Where it comes from.** The release is cut from a `develop` → `main` PR. The
`prepare-release` workflow takes the last released version from crates.io
(`max_version` of the `rusteal` crate, the one source that cannot drift) and
bumps it by the commits the PR adds: `BREAKING CHANGE:` → major, `feat:` →
minor, anything else → patch. It never reads the version from the repository's
files. If nothing that goes into a package changed since the last tag, it skips
the release.
**Where it is written.** The same bump commit writes it everywhere at once:
| `Cargo.toml` | `[workspace.package].version` and the internal `{ version, path }` dependencies | `0.2.1` |
| `ue_plugin/*/*.uplugin` | `VersionName` | `"0.2.1"` |
| `ue_plugin/*/*.uplugin` | `Version` | `2001` |
Tags (`v0.2.1`), crates.io and the manifests only ever use `major.minor.patch`.
**The integer form.** Two places cannot hold `0.2.1`: the `.uplugin` `Version`
field, which UE requires to be an integer, and `RustealApiTable::version`, a
`u32`. Both use the same encoding, `major * 1_000_000 + minor * 1_000 + patch`
(`rusteal_ffi::encode_version`). It is always derived from the version, never
a source of it. Minor and patch must stay below 1000, or the number would be
ambiguous; `encode_version` refuses such a version at compile time, so it cannot
slip through.
**How it is kept in line.**
- `rusteal-cli/tests/plugin_version.rs` fails if either `.uplugin` disagrees with
the workspace version, so a descriptor edited by hand turns CI red.
- At load, the plugin compares its own version with the library's
`rusteal_version()` export and refuses a library built against another one;
`rusteal_runtime::init` checks the table's `version` again.
- Before `build`, `generate` and `setup`, the CLI compares the project's pins
and plugins with its own version (see [Versions](#versions)).
`Cargo.lock` is not versioned: every build would rewrite the internal versions
in it. A dependency release that breaks the workspace shows up in CI, where it
gets fixed. `cargo install rusteal --locked` still works, because cargo packs a
lock file of its own into the published crate.
## License
Licensed under either of:
- Apache License, Version 2.0 ([LICENSE-APACHE](https://github.com/viniciusmorgado/rusteal/blob/main/LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0>)
- MIT license ([LICENSE-MIT](https://github.com/viniciusmorgado/rusteal/blob/main/LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
at your option.