1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
//! In Bevy, states are app-wide interdependent, finite state machines that are generally used to model the large scale structure of your program: whether a game is paused, if the player is in combat, if assets are loaded and so on.
//!
//! This module provides 3 distinct types of state, all of which implement the [`States`](state::States) trait:
//!
//! - Standard [`States`](state::States) can only be changed by manually setting the [`NextState<S>`](state::NextState) resource.
//! These states are the baseline on which the other state types are built, and can be used on
//! their own for many simple patterns. See the [state example](https://github.com/bevyengine/bevy/blob/latest/examples/ecs/state.rs)
//! for a simple use case.
//! - [`SubStates`](state::SubStates) are children of other states - they can be changed manually using [`NextState<S>`](state::NextState),
//! but are removed from the [`World`](bevy_ecs::prelude::World) if the source states aren't in the right state. See the [sub_states example](https://github.com/bevyengine/bevy/blob/latest/examples/ecs/sub_states.rs)
//! for a simple use case based on the derive macro, or read the trait docs for more complex scenarios.
//! - [`ComputedStates`](state::ComputedStates) are fully derived from other states - they provide a [`compute`](state::ComputedStates::compute) method
//! that takes in the source states and returns their derived value. They are particularly useful for situations
//! where a simplified view of the source states is necessary - such as having an `InAMenu` computed state, derived
//! from a source state that defines multiple distinct menus. See the [computed state example](https://github.com/bevyengine/bevy/blob/latest/examples/ecs/computed_states.rs)
//! to see usage samples for these states.
//!
//! Most of the utilities around state involve running systems during transitions between states, or
//! determining whether to run certain systems, though they can be used more directly as well. This
//! makes it easier to transition between menus, add loading screens, pause games, and the more.
//!
//! Specifically, Bevy provides the following utilities:
//!
//! - 3 Transition Schedules - [`OnEnter<S>`](crate::state::OnEnter), [`OnExit<S>`](crate::state::OnExit) and [`OnTransition<S>`](crate::state::OnTransition) - which are used
//! to trigger systems specifically during matching transitions.
//! - A [`StateTransitionEvent<S>`](crate::state::StateTransitionEvent) that gets fired when a given state changes.
//! - The [`in_state<S>`](crate::condition::in_state) and [`state_changed<S>`](crate::condition::state_changed) run conditions - which are used
//! to determine whether a system should run based on the current state.
#[cfg(feature = "bevy_app")]
/// Provides [`App`](bevy_app::App) and [`SubApp`](bevy_app::SubApp) with state installation methods
pub mod app;
/// Provides definitions for the runtime conditions that interact with the state system
pub mod condition;
/// Provides definitions for the basic traits required by the state system
pub mod state;
/// Provides [`StateScoped`] and [`clear_state_scoped_entities`] for managing lifetime of entities.
pub mod state_scoped;
/// Most commonly used re-exported types.
pub mod prelude {
#[cfg(feature = "bevy_app")]
#[doc(hidden)]
pub use crate::app::AppExtStates;
#[doc(hidden)]
pub use crate::condition::*;
#[doc(hidden)]
pub use crate::state::{
last_transition, ComputedStates, EnterSchedules, ExitSchedules, NextState, OnEnter, OnExit,
OnTransition, State, StateSet, StateTransition, StateTransitionEvent, States, SubStates,
TransitionSchedules,
};
#[doc(hidden)]
pub use crate::state_scoped::StateScoped;
}