Trait bevy::state::prelude::ComputedStates

pub trait ComputedStates: 'static + Send + Sync + Clone + PartialEq + Eq + Hash + Debug {
    type SourceStates: StateSet;

    // Required method
    fn compute(sources: Self::SourceStates) -> Option<Self>;

    // Provided method
    fn register_computed_state_systems(schedule: &mut Schedule) { ... }
}

A state whose value is automatically computed based on the values of other States.

A computed state is a state that is deterministically derived from a set of SourceStates. The StateSet is passed into the compute method whenever one of them changes, and the result becomes the state’s value.

/// Computed States require some state to derive from
#[derive(States, Clone, PartialEq, Eq, Hash, Debug, Default)]
enum AppState {
    #[default]
    Menu,
    InGame { paused: bool }
}


#[derive(Clone, PartialEq, Eq, Hash, Debug)]
struct InGame;

impl ComputedStates for InGame {
    /// We set the source state to be the state, or a tuple of states,
    /// we want to depend on. You can also wrap each state in an Option,
    /// if you want the computed state to execute even if the state doesn't
    /// currently exist in the world.
    type SourceStates = AppState;

    /// We then define the compute function, which takes in
    /// your SourceStates
    fn compute(sources: AppState) -> Option<Self> {
        match sources {
            /// When we are in game, we want to return the InGame state
            AppState::InGame { .. } => Some(InGame),
            /// Otherwise, we don't want the `State<InGame>` resource to exist,
            /// so we return None.
            _ => None
        }
    }
}

you can then add it to an App, and from there you use the state as normal

    App::new()
        .init_state::<AppState>()
        .add_computed_state::<InGame>();

Required Associated Types

type SourceStates: StateSet

The set of states from which the Self is derived.

This can either be a single type that implements States, an Option of a type that implements States, or a tuple containing multiple types that implement States or Optional versions of them.

For example, (MapState, EnemyState) is valid, as is (MapState, Option<EnemyState>)

Required Methods

fn compute(sources: Self::SourceStates) -> Option<Self>

Computes the next value of State<Self>. This function gets called whenever one of the SourceStates changes.

If the result is None, the State<Self> resource will be removed from the world.

Provided Methods

fn register_computed_state_systems(schedule: &mut Schedule)

This function sets up systems that compute the state whenever one of the SourceStates change. It is called by App::add_computed_state, but can be called manually if App is not used.

Object Safety

This trait is not object safe.

Implementors