bevy/crates/bevy_ecs/src/schedule/condition.rs
Aldrich Suratos 1e2132672e
Copy over docs for Condition trait from PR #10718 (#10748)
# Objective

Resolves #10743.

## Solution

Copied over the documentation written by @stepancheng from PR #10718.

I left out the lines from the doctest where `<()>` is removed, as that
seemed to be the part people couldn't decide on whether to keep or not.
2023-11-27 16:33:22 +00:00

1216 lines
41 KiB
Rust

use std::borrow::Cow;
use std::ops::Not;
use crate::system::{
Adapt, AdapterSystem, CombinatorSystem, Combine, IntoSystem, ReadOnlySystem, System,
};
/// A type-erased run condition stored in a [`Box`].
pub type BoxedCondition<In = ()> = Box<dyn ReadOnlySystem<In = In, Out = bool>>;
/// A system that determines if one or more scheduled systems should run.
///
/// Implemented for functions and closures that convert into [`System<Out=bool>`](crate::system::System)
/// with [read-only](crate::system::ReadOnlySystemParam) parameters.
///
/// # Marker type parameter
///
/// `Condition` trait has `Marker` type parameter, which has no special meaning,
/// but exists to work around the limitation of Rust's trait system.
///
/// Type parameter in return type can be set to `<()>` by calling [`IntoSystem::into_system`],
/// but usually have to be specified when passing a condition to a function.
///
/// ```
/// # use bevy_ecs::schedule::Condition;
/// # use bevy_ecs::system::IntoSystem;
/// fn not_condition<Marker>(a: impl Condition<Marker>) -> impl Condition<()> {
/// IntoSystem::into_system(a.map(|x| !x))
/// }
/// ```
///
/// # Examples
/// A condition that returns true every other time it's called.
/// ```
/// # use bevy_ecs::prelude::*;
/// fn every_other_time() -> impl Condition<()> {
/// IntoSystem::into_system(|mut flag: Local<bool>| {
/// *flag = !*flag;
/// *flag
/// })
/// }
///
/// # #[derive(Resource)] struct DidRun(bool);
/// # fn my_system(mut did_run: ResMut<DidRun>) { did_run.0 = true; }
/// # let mut schedule = Schedule::default();
/// schedule.add_systems(my_system.run_if(every_other_time()));
/// # let mut world = World::new();
/// # world.insert_resource(DidRun(false));
/// # schedule.run(&mut world);
/// # assert!(world.resource::<DidRun>().0);
/// # world.insert_resource(DidRun(false));
/// # schedule.run(&mut world);
/// # assert!(!world.resource::<DidRun>().0);
/// ```
///
/// A condition that takes a bool as an input and returns it unchanged.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// fn identity() -> impl Condition<(), bool> {
/// IntoSystem::into_system(|In(x)| x)
/// }
///
/// # fn always_true() -> bool { true }
/// # let mut app = Schedule::default();
/// # #[derive(Resource)] struct DidRun(bool);
/// # fn my_system(mut did_run: ResMut<DidRun>) { did_run.0 = true; }
/// app.add_systems(my_system.run_if(always_true.pipe(identity())));
/// # let mut world = World::new();
/// # world.insert_resource(DidRun(false));
/// # app.run(&mut world);
/// # assert!(world.resource::<DidRun>().0);
pub trait Condition<Marker, In = ()>: sealed::Condition<Marker, In> {
/// Returns a new run condition that only returns `true`
/// if both this one and the passed `and_then` return `true`.
///
/// The returned run condition is short-circuiting, meaning
/// `and_then` will only be invoked if `self` returns `true`.
///
/// # Examples
///
/// ```should_panic
/// use bevy_ecs::prelude::*;
///
/// #[derive(Resource, PartialEq)]
/// struct R(u32);
///
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # fn my_system() {}
/// app.add_systems(
/// // The `resource_equals` run condition will panic since we don't initialize `R`,
/// // just like if we used `Res<R>` in a system.
/// my_system.run_if(resource_equals(R(0))),
/// );
/// # app.run(&mut world);
/// ```
///
/// Use `.and_then()` to avoid checking the condition.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, PartialEq)]
/// # struct R(u32);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # fn my_system() {}
/// app.add_systems(
/// // `resource_equals` will only get run if the resource `R` exists.
/// my_system.run_if(resource_exists::<R>().and_then(resource_equals(R(0)))),
/// );
/// # app.run(&mut world);
/// ```
///
/// Note that in this case, it's better to just use the run condition [`resource_exists_and_equals`].
///
/// [`resource_exists_and_equals`]: common_conditions::resource_exists_and_equals
fn and_then<M, C: Condition<M, In>>(self, and_then: C) -> AndThen<Self::System, C::System> {
let a = IntoSystem::into_system(self);
let b = IntoSystem::into_system(and_then);
let name = format!("{} && {}", a.name(), b.name());
CombinatorSystem::new(a, b, Cow::Owned(name))
}
/// Returns a new run condition that returns `true`
/// if either this one or the passed `or_else` return `true`.
///
/// The returned run condition is short-circuiting, meaning
/// `or_else` will only be invoked if `self` returns `false`.
///
/// # Examples
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// #[derive(Resource, PartialEq)]
/// struct A(u32);
///
/// #[derive(Resource, PartialEq)]
/// struct B(u32);
///
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # #[derive(Resource)] struct C(bool);
/// # fn my_system(mut c: ResMut<C>) { c.0 = true; }
/// app.add_systems(
/// // Only run the system if either `A` or `B` exist.
/// my_system.run_if(resource_exists::<A>().or_else(resource_exists::<B>())),
/// );
/// #
/// # world.insert_resource(C(false));
/// # app.run(&mut world);
/// # assert!(!world.resource::<C>().0);
/// #
/// # world.insert_resource(A(0));
/// # app.run(&mut world);
/// # assert!(world.resource::<C>().0);
/// #
/// # world.remove_resource::<A>();
/// # world.insert_resource(B(0));
/// # world.insert_resource(C(false));
/// # app.run(&mut world);
/// # assert!(world.resource::<C>().0);
/// ```
fn or_else<M, C: Condition<M, In>>(self, or_else: C) -> OrElse<Self::System, C::System> {
let a = IntoSystem::into_system(self);
let b = IntoSystem::into_system(or_else);
let name = format!("{} || {}", a.name(), b.name());
CombinatorSystem::new(a, b, Cow::Owned(name))
}
}
impl<Marker, In, F> Condition<Marker, In> for F where F: sealed::Condition<Marker, In> {}
mod sealed {
use crate::system::{IntoSystem, ReadOnlySystem};
pub trait Condition<Marker, In>:
IntoSystem<In, bool, Marker, System = Self::ReadOnlySystem>
{
// This associated type is necessary to let the compiler
// know that `Self::System` is `ReadOnlySystem`.
type ReadOnlySystem: ReadOnlySystem<In = In, Out = bool>;
}
impl<Marker, In, F> Condition<Marker, In> for F
where
F: IntoSystem<In, bool, Marker>,
F::System: ReadOnlySystem,
{
type ReadOnlySystem = F::System;
}
}
/// A collection of [run conditions](Condition) that may be useful in any bevy app.
pub mod common_conditions {
use super::NotSystem;
use crate::{
change_detection::DetectChanges,
event::{Event, EventReader},
prelude::{Component, Query, With},
removal_detection::RemovedComponents,
schedule::{State, States},
system::{IntoSystem, Res, Resource, System},
};
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the first time the condition is run and false every time after
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `run_once` will only return true the first time it's evaluated
/// my_system.run_if(run_once()),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // This is the first time the condition will be evaluated so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// // This is the seconds time the condition will be evaluated so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn run_once() -> impl FnMut() -> bool + Clone {
let mut has_run = false;
move || {
if !has_run {
has_run = true;
true
} else {
false
}
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource exists.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// app.add_systems(
/// // `resource_exists` will only return true if the given resource exists in the world
/// my_system.run_if(resource_exists::<Counter>()),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `Counter` hasn't been added so `my_system` won't run
/// app.run(&mut world);
/// world.init_resource::<Counter>();
///
/// // `Counter` has now been added so `my_system` can run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn resource_exists<T>() -> impl FnMut(Option<Res<T>>) -> bool + Clone
where
T: Resource,
{
move |res: Option<Res<T>>| res.is_some()
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource is equal to `value`.
///
/// # Panics
///
/// The condition will panic if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default, PartialEq)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `resource_equals` will only return true if the given resource equals the given value
/// my_system.run_if(resource_equals(Counter(0))),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `Counter` is `0` so `my_system` can run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// // `Counter` is no longer `0` so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn resource_equals<T>(value: T) -> impl FnMut(Res<T>) -> bool
where
T: Resource + PartialEq,
{
move |res: Res<T>| *res == value
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource exists and is equal to `value`.
///
/// The condition will return `false` if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default, PartialEq)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// app.add_systems(
/// // `resource_exists_and_equals` will only return true
/// // if the given resource exists and equals the given value
/// my_system.run_if(resource_exists_and_equals(Counter(0))),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `Counter` hasn't been added so `my_system` can't run
/// app.run(&mut world);
/// world.init_resource::<Counter>();
///
/// // `Counter` is `0` so `my_system` can run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// // `Counter` is no longer `0` so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn resource_exists_and_equals<T>(value: T) -> impl FnMut(Option<Res<T>>) -> bool
where
T: Resource + PartialEq,
{
move |res: Option<Res<T>>| match res {
Some(res) => *res == value,
None => false,
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource of the given type has been added since the condition was last checked.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// app.add_systems(
/// // `resource_added` will only return true if the
/// // given resource was just added
/// my_system.run_if(resource_added::<Counter>()),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// world.init_resource::<Counter>();
///
/// // `Counter` was just added so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// // `Counter` was not just added so `my_system` will not run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn resource_added<T>() -> impl FnMut(Option<Res<T>>) -> bool + Clone
where
T: Resource,
{
move |res: Option<Res<T>>| match res {
Some(res) => res.is_added(),
None => false,
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource of the given type has had its value changed since the condition
/// was last checked.
///
/// The value is considered changed when it is added. The first time this condition
/// is checked after the resource was added, it will return `true`.
/// Change detection behaves like this everywhere in Bevy.
///
/// # Panics
///
/// The condition will panic if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `resource_changed` will only return true if the
/// // given resource was just changed (or added)
/// my_system.run_if(
/// resource_changed::<Counter>()
/// // By default detecting changes will also trigger if the resource was
/// // just added, this won't work with my example so I will add a second
/// // condition to make sure the resource wasn't just added
/// .and_then(not(resource_added::<Counter>()))
/// ),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `Counter` hasn't been changed so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.resource_mut::<Counter>().0 = 50;
///
/// // `Counter` was just changed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 51);
/// ```
pub fn resource_changed<T>() -> impl FnMut(Res<T>) -> bool + Clone
where
T: Resource,
{
move |res: Res<T>| res.is_changed()
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource of the given type has had its value changed since the condition
/// was last checked.
///
/// The value is considered changed when it is added. The first time this condition
/// is checked after the resource was added, it will return `true`.
/// Change detection behaves like this everywhere in Bevy.
///
/// This run condition does not detect when the resource is removed.
///
/// The condition will return `false` if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// app.add_systems(
/// // `resource_exists_and_changed` will only return true if the
/// // given resource exists and was just changed (or added)
/// my_system.run_if(
/// resource_exists_and_changed::<Counter>()
/// // By default detecting changes will also trigger if the resource was
/// // just added, this won't work with my example so I will add a second
/// // condition to make sure the resource wasn't just added
/// .and_then(not(resource_added::<Counter>()))
/// ),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `Counter` doesn't exist so `my_system` won't run
/// app.run(&mut world);
/// world.init_resource::<Counter>();
///
/// // `Counter` hasn't been changed so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.resource_mut::<Counter>().0 = 50;
///
/// // `Counter` was just changed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 51);
/// ```
pub fn resource_exists_and_changed<T>() -> impl FnMut(Option<Res<T>>) -> bool + Clone
where
T: Resource,
{
move |res: Option<Res<T>>| match res {
Some(res) => res.is_changed(),
None => false,
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource of the given type has had its value changed since the condition
/// was last checked.
///
/// The value is considered changed when it is added. The first time this condition
/// is checked after the resource was added, it will return `true`.
/// Change detection behaves like this everywhere in Bevy.
///
/// This run condition also detects removal. It will return `true` if the resource
/// has been removed since the run condition was last checked.
///
/// The condition will return `false` if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `resource_changed_or_removed` will only return true if the
/// // given resource was just changed or removed (or added)
/// my_system.run_if(
/// resource_changed_or_removed::<Counter>()
/// // By default detecting changes will also trigger if the resource was
/// // just added, this won't work with my example so I will add a second
/// // condition to make sure the resource wasn't just added
/// .and_then(not(resource_added::<Counter>()))
/// ),
/// );
///
/// #[derive(Resource, Default)]
/// struct MyResource;
///
/// // If `Counter` exists, increment it, otherwise insert `MyResource`
/// fn my_system(mut commands: Commands, mut counter: Option<ResMut<Counter>>) {
/// if let Some(mut counter) = counter {
/// counter.0 += 1;
/// } else {
/// commands.init_resource::<MyResource>();
/// }
/// }
///
/// // `Counter` hasn't been changed so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.resource_mut::<Counter>().0 = 50;
///
/// // `Counter` was just changed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 51);
///
/// world.remove_resource::<Counter>();
///
/// // `Counter` was just removed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.contains_resource::<MyResource>(), true);
/// ```
pub fn resource_changed_or_removed<T>() -> impl FnMut(Option<Res<T>>) -> bool + Clone
where
T: Resource,
{
let mut existed = false;
move |res: Option<Res<T>>| {
if let Some(value) = res {
existed = true;
value.is_changed()
} else if existed {
existed = false;
true
} else {
false
}
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the resource of the given type has been removed since the condition was last checked.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `resource_removed` will only return true if the
/// // given resource was just removed
/// my_system.run_if(resource_removed::<MyResource>()),
/// );
///
/// #[derive(Resource, Default)]
/// struct MyResource;
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// world.init_resource::<MyResource>();
///
/// // `MyResource` hasn't just been removed so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.remove_resource::<MyResource>();
///
/// // `MyResource` was just removed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn resource_removed<T>() -> impl FnMut(Option<Res<T>>) -> bool + Clone
where
T: Resource,
{
let mut existed = false;
move |res: Option<Res<T>>| {
if res.is_some() {
existed = true;
false
} else if existed {
existed = false;
true
} else {
false
}
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the state machine exists.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// #[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
/// enum GameState {
/// #[default]
/// Playing,
/// Paused,
/// }
///
/// app.add_systems(
/// // `state_exists` will only return true if the
/// // given state exists
/// my_system.run_if(state_exists::<GameState>()),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `GameState` does not yet exist `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.init_resource::<State<GameState>>();
///
/// // `GameState` now exists so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn state_exists<S: States>() -> impl FnMut(Option<Res<State<S>>>) -> bool + Clone {
move |current_state: Option<Res<State<S>>>| current_state.is_some()
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the state machine is currently in `state`.
///
/// # Panics
///
/// The condition will panic if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// #[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
/// enum GameState {
/// #[default]
/// Playing,
/// Paused,
/// }
///
/// world.init_resource::<State<GameState>>();
///
/// app.add_systems((
/// // `in_state` will only return true if the
/// // given state equals the given value
/// play_system.run_if(in_state(GameState::Playing)),
/// pause_system.run_if(in_state(GameState::Paused)),
/// ));
///
/// fn play_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// fn pause_system(mut counter: ResMut<Counter>) {
/// counter.0 -= 1;
/// }
///
/// // We default to `GameState::Playing` so `play_system` runs
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// *world.resource_mut::<State<GameState>>() = State::new(GameState::Paused);
///
/// // Now that we are in `GameState::Pause`, `pause_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
/// ```
pub fn in_state<S: States>(state: S) -> impl FnMut(Res<State<S>>) -> bool + Clone {
move |current_state: Res<State<S>>| *current_state == state
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the state machine exists and is currently in `state`.
///
/// The condition will return `false` if the state does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// #[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
/// enum GameState {
/// #[default]
/// Playing,
/// Paused,
/// }
///
/// app.add_systems((
/// // `state_exists_and_equals` will only return true if the
/// // given state exists and equals the given value
/// play_system.run_if(state_exists_and_equals(GameState::Playing)),
/// pause_system.run_if(state_exists_and_equals(GameState::Paused)),
/// ));
///
/// fn play_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// fn pause_system(mut counter: ResMut<Counter>) {
/// counter.0 -= 1;
/// }
///
/// // `GameState` does not yet exists so neither system will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.init_resource::<State<GameState>>();
///
/// // We default to `GameState::Playing` so `play_system` runs
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// *world.resource_mut::<State<GameState>>() = State::new(GameState::Paused);
///
/// // Now that we are in `GameState::Pause`, `pause_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
/// ```
pub fn state_exists_and_equals<S: States>(
state: S,
) -> impl FnMut(Option<Res<State<S>>>) -> bool + Clone {
move |current_state: Option<Res<State<S>>>| match current_state {
Some(current_state) => *current_state == state,
None => false,
}
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if the state machine changed state.
///
/// To do things on transitions to/from specific states, use their respective OnEnter/OnExit
/// schedules. Use this run condition if you want to detect any change, regardless of the value.
///
/// # Panics
///
/// The condition will panic if the resource does not exist.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// #[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
/// enum GameState {
/// #[default]
/// Playing,
/// Paused,
/// }
///
/// world.init_resource::<State<GameState>>();
///
/// app.add_systems(
/// // `state_changed` will only return true if the
/// // given states value has just been updated or
/// // the state has just been added
/// my_system.run_if(state_changed::<GameState>()),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // `GameState` has just been added so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// // `GameState` has not been updated so `my_system` will not run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
///
/// *world.resource_mut::<State<GameState>>() = State::new(GameState::Paused);
///
/// // Now that `GameState` has been updated `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 2);
/// ```
pub fn state_changed<S: States>() -> impl FnMut(Res<State<S>>) -> bool + Clone {
move |current_state: Res<State<S>>| current_state.is_changed()
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if there are any new events of the given type since it was last called.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// # world.init_resource::<Events<MyEvent>>();
/// # app.add_systems(bevy_ecs::event::event_update_system::<MyEvent>.before(my_system));
///
/// app.add_systems(
/// my_system.run_if(on_event::<MyEvent>()),
/// );
///
/// #[derive(Event)]
/// struct MyEvent;
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // No new `MyEvent` events have been push so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.resource_mut::<Events<MyEvent>>().send(MyEvent);
///
/// // A `MyEvent` event has been pushed so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn on_event<T: Event>() -> impl FnMut(EventReader<T>) -> bool + Clone {
// The events need to be consumed, so that there are no false positives on subsequent
// calls of the run condition. Simply checking `is_empty` would not be enough.
// PERF: note that `count` is efficient (not actually looping/iterating),
// due to Bevy having a specialized implementation for events.
move |mut reader: EventReader<T>| reader.read().count() > 0
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if there are any entities with the given component type.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// my_system.run_if(any_with_component::<MyComponent>()),
/// );
///
/// #[derive(Component)]
/// struct MyComponent;
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// // No entities exist yet with a `MyComponent` component so `my_system` won't run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
///
/// world.spawn(MyComponent);
///
/// // An entities with `MyComponent` now exists so `my_system` will run
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 1);
/// ```
pub fn any_with_component<T: Component>() -> impl FnMut(Query<(), With<T>>) -> bool + Clone {
move |query: Query<(), With<T>>| !query.is_empty()
}
/// Generates a [`Condition`](super::Condition)-satisfying closure that returns `true`
/// if there are any entity with a component of the given type removed.
pub fn any_component_removed<T: Component>() -> impl FnMut(RemovedComponents<T>) -> bool {
// `RemovedComponents` based on events and therefore events need to be consumed,
// so that there are no false positives on subsequent calls of the run condition.
// Simply checking `is_empty` would not be enough.
// PERF: note that `count` is efficient (not actually looping/iterating),
// due to Bevy having a specialized implementation for events.
move |mut removals: RemovedComponents<T>| removals.read().count() != 0
}
/// Generates a [`Condition`](super::Condition) that inverses the result of passed one.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Resource, Default)]
/// # struct Counter(u8);
/// # let mut app = Schedule::default();
/// # let mut world = World::new();
/// # world.init_resource::<Counter>();
/// app.add_systems(
/// // `not` will inverse any condition you pass in.
/// // Since the condition we choose always returns true
/// // this system will never run
/// my_system.run_if(not(always)),
/// );
///
/// fn my_system(mut counter: ResMut<Counter>) {
/// counter.0 += 1;
/// }
///
/// fn always() -> bool {
/// true
/// }
///
/// app.run(&mut world);
/// assert_eq!(world.resource::<Counter>().0, 0);
/// ```
pub fn not<Marker, TOut, T>(condition: T) -> NotSystem<T::System>
where
TOut: std::ops::Not,
T: IntoSystem<(), TOut, Marker>,
{
let condition = IntoSystem::into_system(condition);
let name = format!("!{}", condition.name());
NotSystem::new(super::NotMarker, condition, name.into())
}
}
/// Invokes [`Not`] with the output of another system.
///
/// See [`common_conditions::not`] for examples.
pub type NotSystem<T> = AdapterSystem<NotMarker, T>;
/// Used with [`AdapterSystem`] to negate the output of a system via the [`Not`] operator.
#[doc(hidden)]
#[derive(Clone, Copy)]
pub struct NotMarker;
impl<T: System> Adapt<T> for NotMarker
where
T::Out: Not,
{
type In = T::In;
type Out = <T::Out as Not>::Output;
fn adapt(&mut self, input: Self::In, run_system: impl FnOnce(T::In) -> T::Out) -> Self::Out {
!run_system(input)
}
}
/// Combines the outputs of two systems using the `&&` operator.
pub type AndThen<A, B> = CombinatorSystem<AndThenMarker, A, B>;
/// Combines the outputs of two systems using the `||` operator.
pub type OrElse<A, B> = CombinatorSystem<OrElseMarker, A, B>;
#[doc(hidden)]
pub struct AndThenMarker;
impl<In, A, B> Combine<A, B> for AndThenMarker
where
In: Copy,
A: System<In = In, Out = bool>,
B: System<In = In, Out = bool>,
{
type In = In;
type Out = bool;
fn combine(
input: Self::In,
a: impl FnOnce(<A as System>::In) -> <A as System>::Out,
b: impl FnOnce(<B as System>::In) -> <B as System>::Out,
) -> Self::Out {
a(input) && b(input)
}
}
#[doc(hidden)]
pub struct OrElseMarker;
impl<In, A, B> Combine<A, B> for OrElseMarker
where
In: Copy,
A: System<In = In, Out = bool>,
B: System<In = In, Out = bool>,
{
type In = In;
type Out = bool;
fn combine(
input: Self::In,
a: impl FnOnce(<A as System>::In) -> <A as System>::Out,
b: impl FnOnce(<B as System>::In) -> <B as System>::Out,
) -> Self::Out {
a(input) || b(input)
}
}
#[cfg(test)]
mod tests {
use super::{common_conditions::*, Condition};
use crate as bevy_ecs;
use crate::component::Component;
use crate::schedule::IntoSystemConfigs;
use crate::schedule::{common_conditions::not, State, States};
use crate::system::Local;
use crate::{change_detection::ResMut, schedule::Schedule, world::World};
use bevy_ecs_macros::Event;
use bevy_ecs_macros::Resource;
#[derive(Resource, Default)]
struct Counter(usize);
fn increment_counter(mut counter: ResMut<Counter>) {
counter.0 += 1;
}
fn every_other_time(mut has_ran: Local<bool>) -> bool {
*has_ran = !*has_ran;
*has_ran
}
#[test]
fn run_condition() {
let mut world = World::new();
world.init_resource::<Counter>();
let mut schedule = Schedule::default();
// Run every other cycle
schedule.add_systems(increment_counter.run_if(every_other_time));
schedule.run(&mut world);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);
schedule.run(&mut world);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 2);
// Run every other cycle opposite to the last one
schedule.add_systems(increment_counter.run_if(not(every_other_time)));
schedule.run(&mut world);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 4);
schedule.run(&mut world);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 6);
}
#[test]
fn run_condition_combinators() {
let mut world = World::new();
world.init_resource::<Counter>();
let mut schedule = Schedule::default();
// Always run
schedule.add_systems(increment_counter.run_if(every_other_time.or_else(|| true)));
// Run every other cycle
schedule.add_systems(increment_counter.run_if(every_other_time.and_then(|| true)));
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 2);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 3);
}
#[test]
fn multiple_run_conditions() {
let mut world = World::new();
world.init_resource::<Counter>();
let mut schedule = Schedule::default();
// Run every other cycle
schedule.add_systems(increment_counter.run_if(every_other_time).run_if(|| true));
// Never run
schedule.add_systems(increment_counter.run_if(every_other_time).run_if(|| false));
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);
}
#[test]
fn multiple_run_conditions_is_and_operation() {
let mut world = World::new();
world.init_resource::<Counter>();
let mut schedule = Schedule::default();
// This should never run, if multiple run conditions worked
// like an OR condition then it would always run
schedule.add_systems(
increment_counter
.run_if(every_other_time)
.run_if(not(every_other_time)),
);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);
schedule.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);
}
#[derive(States, PartialEq, Eq, Debug, Default, Hash, Clone)]
enum TestState {
#[default]
A,
B,
}
#[derive(Component)]
struct TestComponent;
#[derive(Event)]
struct TestEvent;
fn test_system() {}
// Ensure distributive_run_if compiles with the common conditions.
#[test]
fn distributive_run_if_compiles() {
Schedule::default().add_systems(
(test_system, test_system)
.distributive_run_if(run_once())
.distributive_run_if(resource_exists::<State<TestState>>())
.distributive_run_if(resource_added::<State<TestState>>())
.distributive_run_if(resource_changed::<State<TestState>>())
.distributive_run_if(resource_exists_and_changed::<State<TestState>>())
.distributive_run_if(resource_changed_or_removed::<State<TestState>>())
.distributive_run_if(resource_removed::<State<TestState>>())
.distributive_run_if(state_exists::<TestState>())
.distributive_run_if(in_state(TestState::A).or_else(in_state(TestState::B)))
.distributive_run_if(state_changed::<TestState>())
.distributive_run_if(on_event::<TestEvent>())
.distributive_run_if(any_with_component::<TestComponent>())
.distributive_run_if(not(run_once())),
);
}
}