//! Types that detect when their internal data mutate.
use crate::{component::ComponentTicks, ptr::PtrMut, system::Resource};
use std::ops::{Deref, DerefMut};
/// The (arbitrarily chosen) minimum number of world tick increments between `check_tick` scans.
///
/// Change ticks can only be scanned when systems aren't running. Thus, if the threshold is `N`,
/// the maximum is `2 * N - 1` (i.e. the world ticks `N - 1` times, then `N` times).
///
/// If no change is older than `u32::MAX - (2 * N - 1)` following a scan, none of their ages can
/// overflow and cause false positives.
// (518,400,000 = 1000 ticks per frame * 144 frames per second * 3600 seconds per hour)
pub const CHECK_TICK_THRESHOLD: u32 = 518_400_000;
/// The maximum change tick difference that won't overflow before the next `check_tick` scan.
///
/// Changes stop being detected once they become this old.
pub const MAX_CHANGE_AGE: u32 = u32::MAX - (2 * CHECK_TICK_THRESHOLD - 1);
/// Types that implement reliable change detection.
///
/// ## Example
/// Using types that implement [`DetectChanges`], such as [`ResMut`], provide
/// a way to query if a value has been mutated in another system.
/// Normally change detecting is triggered by either [`DerefMut`] or [`AsMut`], however
/// it can be manually triggered via [`DetectChanges::set_changed`].
///
/// ```
/// use bevy_ecs::prelude::*;
///
/// #[derive(Resource)]
/// struct MyResource(u32);
///
/// fn my_system(mut resource: ResMut<MyResource>) {
/// if resource.is_changed() {
/// println!("My resource was mutated!");
/// }
///
/// resource.0 = 42; // triggers change detection via [`DerefMut`]
/// }
/// ```
///
pub trait DetectChanges {
/// The type contained within this smart pointer
///
/// For example, for `Res<T>` this would be `T`.
type Inner: ?Sized;
/// Returns `true` if this value was added after the system last ran.
fn is_added(&self) -> bool;
/// Returns `true` if this value was added or mutably dereferenced after the system last ran.
fn is_changed(&self) -> bool;
/// Flags this value as having been changed.
///
/// Mutably accessing this smart pointer will automatically flag this value as having been changed.
/// However, mutation through interior mutability requires manual reporting.
///
/// **Note**: This operation cannot be undone.
fn set_changed(&mut self);
/// Returns the change tick recording the previous time this data was changed.
///
/// Note that components and resources are also marked as changed upon insertion.
///
/// For comparison, the previous change tick of a system can be read using the
/// [`SystemChangeTick`](crate::system::SystemChangeTick)
/// [`SystemParam`](crate::system::SystemParam).
fn last_changed(&self) -> u32;
/// Manually sets the change tick recording the previous time this data was mutated.
///
/// # Warning
/// This is a complex and error-prone operation, primarily intended for use with rollback networking strategies.
/// If you merely want to flag this data as changed, use [`set_changed`](DetectChanges::set_changed) instead.
/// If you want to avoid triggering change detection, use [`bypass_change_detection`](DetectChanges::bypass_change_detection) instead.
fn set_last_changed(&mut self, last_change_tick: u32);
/// Manually bypasses change detection, allowing you to mutate the underlying value without updating the change tick.
///
/// # Warning
/// This is a risky operation, that can have unexpected consequences on any system relying on this code.
/// However, it can be an essential escape hatch when, for example,
/// you are trying to synchronize representations using change detection and need to avoid infinite recursion.
fn bypass_change_detection(&mut self) -> &mut Self::Inner;
}
macro_rules! change_detection_impl {
($name:ident < $( $generics:tt ),+ >, $target:ty, $($traits:ident)?) => {
impl<$($generics),* : ?Sized $(+ $traits)?> DetectChanges for $name<$($generics),*> {
type Inner = $target;
#[inline]
fn is_added(&self) -> bool {
self.ticks
.component_ticks
.is_added(self.ticks.last_change_tick, self.ticks.change_tick)
}
#[inline]
fn is_changed(&self) -> bool {
self.ticks
.component_ticks
.is_changed(self.ticks.last_change_tick, self.ticks.change_tick)
}
#[inline]
fn set_changed(&mut self) {
self.ticks
.component_ticks
.set_changed(self.ticks.change_tick);
}
#[inline]
fn last_changed(&self) -> u32 {
self.ticks.last_change_tick
}
#[inline]
fn set_last_changed(&mut self, last_change_tick: u32) {
self.ticks.last_change_tick = last_change_tick
}
#[inline]
fn bypass_change_detection(&mut self) -> &mut Self::Inner {
self.value
}
}
impl<$($generics),*: ?Sized $(+ $traits)?> Deref for $name<$($generics),*> {
type Target = $target;
#[inline]
fn deref(&self) -> &Self::Target {
self.value
}
}
impl<$($generics),* : ?Sized $(+ $traits)?> DerefMut for $name<$($generics),*> {
#[inline]
fn deref_mut(&mut self) -> &mut Self::Target {
self.set_changed();
self.value
}
}
impl<$($generics),* $(: $traits)?> AsRef<$target> for $name<$($generics),*> {
#[inline]
fn as_ref(&self) -> &$target {
self.deref()
}
}
impl<$($generics),* $(: $traits)?> AsMut<$target> for $name<$($generics),*> {
#[inline]
fn as_mut(&mut self) -> &mut $target {
self.deref_mut()
}
}
};
}
macro_rules! impl_methods {
($name:ident < $( $generics:tt ),+ >, $target:ty, $($traits:ident)?) => {
impl<$($generics),* : ?Sized $(+ $traits)?> $name<$($generics),*> {
/// Consume `self` and return a mutable reference to the
/// contained value while marking `self` as "changed".
#[inline]
pub fn into_inner(mut self) -> &'a mut $target {
self.set_changed();
self.value
}
/// Maps to an inner value by applying a function to the contained reference, without flagging a change.
///
/// You should never modify the argument passed to the closure -- if you want to modify the data
/// without flagging a change, consider using [`DetectChanges::bypass_change_detection`] to make your intent explicit.
///
/// ```rust
/// # use bevy_ecs::prelude::*;
/// # pub struct Vec2;
/// # impl Vec2 { pub const ZERO: Self = Self; }
/// # #[derive(Component)] pub struct Transform { translation: Vec2 }
/// # mod my_utils {
/// # pub fn set_if_not_equal<T>(x: bevy_ecs::prelude::Mut<T>, val: T) { unimplemented!() }
/// # }
/// // When run, zeroes the translation of every entity.
/// fn reset_positions(mut transforms: Query<&mut Transform>) {
/// for transform in &mut transforms {
/// // We pinky promise not to modify `t` within the closure.
/// // Breaking this promise will result in logic errors, but will never cause undefined behavior.
/// let translation = transform.map_unchanged(|t| &mut t.translation);
/// // Only reset the translation if it isn't already zero;
/// my_utils::set_if_not_equal(translation, Vec2::ZERO);
/// }
/// }
/// # bevy_ecs::system::assert_is_system(reset_positions);
/// ```
pub fn map_unchanged<U: ?Sized>(self, f: impl FnOnce(&mut $target) -> &mut U) -> Mut<'a, U> {
Mut {
value: f(self.value),
ticks: self.ticks,
}
}
}
};
}
macro_rules! impl_debug {
($name:ident < $( $generics:tt ),+ >, $($traits:ident)?) => {
impl<$($generics),* : ?Sized $(+ $traits)?> std::fmt::Debug for $name<$($generics),*>
where T: std::fmt::Debug
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_tuple(stringify!($name))
.field(&self.value)
.finish()
}
}
};
}
pub(crate) struct Ticks<'a> {
pub(crate) component_ticks: &'a mut ComponentTicks,
pub(crate) last_change_tick: u32,
pub(crate) change_tick: u32,
}
/// Unique mutable borrow of a [`Resource`].
///
/// See the [`Resource`] documentation for usage.
///
/// If you need a shared borrow, use [`Res`](crate::system::Res) instead.
///
/// # Panics
///
/// Panics when used as a [`SystemParam`](crate::system::SystemParam) if the resource does not exist.
///
/// Use `Option<ResMut<T>>` instead if the resource might not always exist.
pub struct ResMut<'a, T: ?Sized + Resource> {
pub(crate) value: &'a mut T,
pub(crate) ticks: Ticks<'a>,
}
impl<'w, 'a, T: Resource> IntoIterator for &'a ResMut<'w, T>
where
&'a T: IntoIterator,
{
type Item = <&'a T as IntoIterator>::Item;
type IntoIter = <&'a T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.value.into_iter()
}
}
impl<'w, 'a, T: Resource> IntoIterator for &'a mut ResMut<'w, T>
where
&'a mut T: IntoIterator,
{
type Item = <&'a mut T as IntoIterator>::Item;
type IntoIter = <&'a mut T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.set_changed();
self.value.into_iter()
}
}
change_detection_impl!(ResMut<'a, T>, T, Resource);
impl_methods!(ResMut<'a, T>, T, Resource);
impl_debug!(ResMut<'a, T>, Resource);
impl<'a, T: Resource> From<ResMut<'a, T>> for Mut<'a, T> {
/// Convert this `ResMut` into a `Mut`. This allows keeping the change-detection feature of `Mut`
/// while losing the specificity of `ResMut` for resources.
fn from(other: ResMut<'a, T>) -> Mut<'a, T> {
Mut {
value: other.value,
ticks: other.ticks,
}
}
}
/// Unique borrow of a non-[`Send`] resource.
///
/// Only [`Send`] resources may be accessed with the [`ResMut`] [`SystemParam`](crate::system::SystemParam). In case that the
/// resource does not implement `Send`, this `SystemParam` wrapper can be used. This will instruct
/// the scheduler to instead run the system on the main thread so that it doesn't send the resource
/// over to another thread.
///
/// # Panics
///
/// Panics when used as a `SystemParameter` if the resource does not exist.
///
/// Use `Option<NonSendMut<T>>` instead if the resource might not always exist.
pub struct NonSendMut<'a, T: ?Sized + 'static> {
pub(crate) value: &'a mut T,
pub(crate) ticks: Ticks<'a>,
}
change_detection_impl!(NonSendMut<'a, T>, T,);
impl_methods!(NonSendMut<'a, T>, T,);
impl_debug!(NonSendMut<'a, T>,);
impl<'a, T: 'static> From<NonSendMut<'a, T>> for Mut<'a, T> {
/// Convert this `NonSendMut` into a `Mut`. This allows keeping the change-detection feature of `Mut`
/// while losing the specificity of `NonSendMut`.
fn from(other: NonSendMut<'a, T>) -> Mut<'a, T> {
Mut {
value: other.value,
ticks: other.ticks,
}
}
}
/// Unique mutable borrow of an entity's component
pub struct Mut<'a, T: ?Sized> {
pub(crate) value: &'a mut T,
pub(crate) ticks: Ticks<'a>,
}
impl<'w, 'a, T> IntoIterator for &'a Mut<'w, T>
where
&'a T: IntoIterator,
{
type Item = <&'a T as IntoIterator>::Item;
type IntoIter = <&'a T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.value.into_iter()
}
}
impl<'w, 'a, T> IntoIterator for &'a mut Mut<'w, T>
where
&'a mut T: IntoIterator,
{
type Item = <&'a mut T as IntoIterator>::Item;
type IntoIter = <&'a mut T as IntoIterator>::IntoIter;
fn into_iter(self) -> Self::IntoIter {
self.set_changed();
self.value.into_iter()
}
}
change_detection_impl!(Mut<'a, T>, T,);
impl_methods!(Mut<'a, T>, T,);
impl_debug!(Mut<'a, T>,);
/// Unique mutable borrow of resources or an entity's component.
///
/// Similar to [`Mut`], but not generic over the component type, instead
/// exposing the raw pointer as a `*mut ()`.
///
/// Usually you don't need to use this and can instead use the APIs returning a
/// [`Mut`], but in situations where the types are not known at compile time
/// or are defined outside of rust this can be used.
pub struct MutUntyped<'a> {
pub(crate) value: PtrMut<'a>,
pub(crate) ticks: Ticks<'a>,
}
impl<'a> MutUntyped<'a> {
/// Returns the pointer to the value, without marking it as changed.
///
/// In order to mark the value as changed, you need to call [`set_changed`](DetectChanges::set_changed) manually.
#[inline]
pub fn into_inner(self) -> PtrMut<'a> {
self.value
}
}
impl<'a> DetectChanges for MutUntyped<'a> {
type Inner = PtrMut<'a>;
#[inline]
fn is_added(&self) -> bool {
self.ticks
.component_ticks
.is_added(self.ticks.last_change_tick, self.ticks.change_tick)
}
#[inline]
fn is_changed(&self) -> bool {
self.ticks
.component_ticks
.is_changed(self.ticks.last_change_tick, self.ticks.change_tick)
}
#[inline]
fn set_changed(&mut self) {
self.ticks
.component_ticks
.set_changed(self.ticks.change_tick);
}
#[inline]
fn last_changed(&self) -> u32 {
self.ticks.last_change_tick
}
#[inline]
fn set_last_changed(&mut self, last_change_tick: u32) {
self.ticks.last_change_tick = last_change_tick;
}
#[inline]
fn bypass_change_detection(&mut self) -> &mut Self::Inner {
&mut self.value
}
}
impl std::fmt::Debug for MutUntyped<'_> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_tuple("MutUntyped")
.field(&self.value.as_ptr())
.finish()
}
}
#[cfg(test)]
mod tests {
use bevy_ecs_macros::Resource;
use crate::{
self as bevy_ecs,
change_detection::{
ComponentTicks, Mut, NonSendMut, ResMut, Ticks, CHECK_TICK_THRESHOLD, MAX_CHANGE_AGE,
},
component::Component,
query::ChangeTrackers,
system::{IntoSystem, Query, System},
world::World,
};
#[derive(Component)]
struct C;
#[derive(Resource)]
struct R;
#[test]
fn change_expiration() {
fn change_detected(query: Query<ChangeTrackers<C>>) -> bool {
query.single().is_changed()
}
fn change_expired(query: Query<ChangeTrackers<C>>) -> bool {
query.single().is_changed()
}
let mut world = World::new();
// component added: 1, changed: 1
world.spawn(C);
let mut change_detected_system = IntoSystem::into_system(change_detected);
let mut change_expired_system = IntoSystem::into_system(change_expired);
change_detected_system.initialize(&mut world);
change_expired_system.initialize(&mut world);
// world: 1, system last ran: 0, component changed: 1
// The spawn will be detected since it happened after the system "last ran".
assert!(change_detected_system.run((), &mut world));
// world: 1 + MAX_CHANGE_AGE
let change_tick = world.change_tick.get_mut();
*change_tick = change_tick.wrapping_add(MAX_CHANGE_AGE);
// Both the system and component appeared `MAX_CHANGE_AGE` ticks ago.
// Since we clamp things to `MAX_CHANGE_AGE` for determinism,
// `ComponentTicks::is_changed` will now see `MAX_CHANGE_AGE > MAX_CHANGE_AGE`
// and return `false`.
assert!(!change_expired_system.run((), &mut world));
}
#[test]
fn change_tick_wraparound() {
fn change_detected(query: Query<ChangeTrackers<C>>) -> bool {
query.single().is_changed()
}
let mut world = World::new();
world.last_change_tick = u32::MAX;
*world.change_tick.get_mut() = 0;
// component added: 0, changed: 0
world.spawn(C);
// system last ran: u32::MAX
let mut change_detected_system = IntoSystem::into_system(change_detected);
change_detected_system.initialize(&mut world);
// Since the world is always ahead, as long as changes can't get older than `u32::MAX` (which we ensure),
// the wrapping difference will always be positive, so wraparound doesn't matter.
assert!(change_detected_system.run((), &mut world));
}
#[test]
fn change_tick_scan() {
let mut world = World::new();
// component added: 1, changed: 1
world.spawn(C);
// a bunch of stuff happens, the component is now older than `MAX_CHANGE_AGE`
*world.change_tick.get_mut() += MAX_CHANGE_AGE + CHECK_TICK_THRESHOLD;
let change_tick = world.change_tick();
let mut query = world.query::<ChangeTrackers<C>>();
for tracker in query.iter(&world) {
let ticks_since_insert = change_tick.wrapping_sub(tracker.component_ticks.added);
let ticks_since_change = change_tick.wrapping_sub(tracker.component_ticks.changed);
assert!(ticks_since_insert > MAX_CHANGE_AGE);
assert!(ticks_since_change > MAX_CHANGE_AGE);
}
// scan change ticks and clamp those at risk of overflow
world.check_change_ticks();
for tracker in query.iter(&world) {
let ticks_since_insert = change_tick.wrapping_sub(tracker.component_ticks.added);
let ticks_since_change = change_tick.wrapping_sub(tracker.component_ticks.changed);
assert!(ticks_since_insert == MAX_CHANGE_AGE);
assert!(ticks_since_change == MAX_CHANGE_AGE);
}
}
#[test]
fn mut_from_res_mut() {
let mut component_ticks = ComponentTicks {
added: 1,
changed: 2,
};
let ticks = Ticks {
component_ticks: &mut component_ticks,
last_change_tick: 3,
change_tick: 4,
};
let mut res = R {};
let res_mut = ResMut {
value: &mut res,
ticks,
};
let into_mut: Mut<R> = res_mut.into();
assert_eq!(1, into_mut.ticks.component_ticks.added);
assert_eq!(2, into_mut.ticks.component_ticks.changed);
assert_eq!(3, into_mut.ticks.last_change_tick);
assert_eq!(4, into_mut.ticks.change_tick);
}
#[test]
fn mut_from_non_send_mut() {
let mut component_ticks = ComponentTicks {
added: 1,
changed: 2,
};
let ticks = Ticks {
component_ticks: &mut component_ticks,
last_change_tick: 3,
change_tick: 4,
};
let mut res = R {};
let non_send_mut = NonSendMut {
value: &mut res,
ticks,
};
let into_mut: Mut<R> = non_send_mut.into();
assert_eq!(1, into_mut.ticks.component_ticks.added);
assert_eq!(2, into_mut.ticks.component_ticks.changed);
assert_eq!(3, into_mut.ticks.last_change_tick);
assert_eq!(4, into_mut.ticks.change_tick);
}
#[test]
fn map_mut() {
use super::*;
struct Outer(i64);
let mut component_ticks = ComponentTicks {
added: 1,
changed: 2,
};
let (last_change_tick, change_tick) = (2, 3);
let ticks = Ticks {
component_ticks: &mut component_ticks,
last_change_tick,
change_tick,
};
let mut outer = Outer(0);
let ptr = Mut {
value: &mut outer,
ticks,
};
assert!(!ptr.is_changed());
// Perform a mapping operation.
let mut inner = ptr.map_unchanged(|x| &mut x.0);
assert!(!inner.is_changed());
// Mutate the inner value.
*inner = 64;
assert!(inner.is_changed());
// Modifying one field of a component should flag a change for the entire component.
assert!(component_ticks.is_changed(last_change_tick, change_tick));
}
}