Struct App 

pub struct App { /* private fields */ }

The central application object.

App owns the ECS world, resources, plugins, and systems. The typical lifecycle is:

1. Create with App::new.
2. Register plugins with add_plugin.
3. Call build to run all plugin registrations and sort systems.
4. Call run to hand control to the runner.

Implementations

impl App

pub fn new() -> Self

Create a new App with an empty world and a default infinite-loop runner.

Builds in TimePlugin — Res<Time> works without registering anything yourself — along with AudioPlugin (Res<AudioOutput>), and, on every target except wasm32, GamepadPlugin (Res<Gamepads>).

pub fn add_plugin(&mut self, plugin: impl Plugin) -> &mut Self

Queue a plugin to be built during build.

pub fn set_ready_gate<F>(&mut self, gate: F) -> &mut Self

where F: FnMut(&mut World, &mut Resources) -> bool + 'static,

Hold every stage idle until gate reports readiness.

gate is called once per update tick — instead of running any SystemStage — for as long as it returns false. As soon as it returns true, it is dropped and update goes back to running stages normally, forever after; there is no re-checking, so gate should only report true once its readiness condition can never become false again (e.g. inserting a resource that is never removed).

Only one gate can be active — a second call replaces the first — since this is meant for a single startup precondition (e.g. an in-flight async GPU backend init on wasm32, which can’t be waited on by blocking the only thread the browser gives it), not general scheduling.

pub fn add_resource(&mut self, res: impl Component) -> &mut Self

Insert a resource into the world immediately.

pub fn get_resource<'a, T: Component>(&'a self) -> Ref<'a, T>

Borrow resource T, panicking if it is absent.

pub fn get_resource_mut<'a, T: Component>(&'a self) -> RefMut<'a, T>

Mutably borrow resource T, panicking if it is absent.

pub fn try_insert_resource<T: Component>(&mut self, res: T) -> bool

Insert resource T only if it is not already present.

Returns true if the resource was inserted.

pub fn add_event<T: Component>(&mut self) -> &mut Self

Register event type T, making EventWriter<T> and EventReader<T> usable as system parameters.

pub fn add_async_event<T: Component>(&mut self) -> &mut Self

Register event type T as in add_event, and additionally make AsyncEventWriter<T> usable as a system parameter.

pub fn add_system<Marker>( &mut self, stage: SystemStage, system: impl IntoSystem<Marker> + 'static, ) -> &mut Self

Register a single system to run at stage.

pub fn add_systems<Marker>( &mut self, stage: SystemStage, systems: impl IntoSystemSet<Marker>, ) -> &mut Self

Register multiple systems to run at stage.

Accepts a tuple of systems via IntoSystemSet.

pub fn build(&mut self) -> &mut Self

Build all plugins and sort systems.

Plugins may register additional plugins during their build call; this repeats until no new plugins are added, up to a hard limit of 64 passes to catch accidental infinite registration cycles.

pub fn update(&mut self)

Run every stage once per tick, in [ALL_STAGES] order — unless a ready_gate is still pending, in which case this tick only checks the gate and returns.

pub fn set_runner<F>(&mut self, runner: F) -> &mut Self

where F: FnOnce(App) + 'static,

Replace the default runner with a custom one.

The runner receives ownership of the App and is responsible for calling update at the appropriate cadence (e.g. driven by a window event loop).

pub fn run(&mut self)

Consume the app and hand it to the configured runner.

Panics if no runner has been set.

Trait Implementations

impl Default for App

fn default() -> Self

Returns the “default value” for a type.