mutate observer

Cargo.toml

@@ -2914,6 +2914,17 @@ description = "Demonstrates how to create a node with a border"
 category = "UI (User Interface)"
 wasm = true
 
+[[example]]
+name = "responding_to_changes"
+path = "examples/ecs/responding_to_changes.rs"
+doc-scrape-examples = true
+
+[package.metadata.example.reactivity]
+name = "Responding to Changes"
+description = "Demonstrates how and when to use change detection and `OnMutate` hooks and observers"
+category = "ECS (Entity Component System)"
+wasm = true
+
 [[example]]
 name = "box_shadow"
 path = "examples/ui/box_shadow.rs"

crates/bevy_ecs/macros/src/world_query.rs

@@ -151,6 +151,7 @@ pub(crate) fn world_query_impl(
             }
 
             const IS_DENSE: bool = true #(&& <#field_types>::IS_DENSE)*;
+            const IS_MUTATE: bool = false #(|| <#field_types>::IS_MUTATE)*;
 
             /// SAFETY: we call `set_archetype` for each member that implements `Fetch`
             #[inline]

crates/bevy_ecs/src/archetype.rs

@@ -352,6 +352,7 @@ bitflags::bitflags! {
         const ON_INSERT_OBSERVER = (1 << 5);
         const ON_REPLACE_OBSERVER = (1 << 6);
         const ON_REMOVE_OBSERVER = (1 << 7);
+        const ON_MUTATE_OBSERVER = (1 << 8);
     }
 }
 
@@ -697,6 +698,12 @@ impl Archetype {
     pub fn has_remove_observer(&self) -> bool {
         self.flags().contains(ArchetypeFlags::ON_REMOVE_OBSERVER)
     }
+
+    /// Returns true if any of the components in this archetype have at least one [`OnMutate`] observer
+    #[inline]
+    pub fn has_mutate_observer(&self) -> bool {
+        self.flags().contains(ArchetypeFlags::ON_MUTATE_OBSERVER)
+    }
 }
 
 /// The next [`ArchetypeId`] in an [`Archetypes`] collection.

crates/bevy_ecs/src/change_detection.rs

@@ -10,11 +10,13 @@ use core::{
     mem,
     ops::{Deref, DerefMut},
 };
+use std::cell::RefCell;
 #[cfg(feature = "track_change_detection")]
 use {
     bevy_ptr::ThinSlicePtr,
     core::{cell::UnsafeCell, panic::Location},
 };
+use crate::storage::{EntityChange, EntityChanges};
 
 /// The (arbitrarily chosen) minimum number of world tick increments between `check_tick` scans.
 ///
@@ -387,6 +389,7 @@ macro_rules! impl_methods {
             /// <T>`, but you need a `Mut<T>`.
             pub fn reborrow(&mut self) -> Mut<'_, $target> {
                 Mut {
+                    on_change: self.on_change,
                     value: self.value,
                     ticks: TicksMut {
                         added: self.ticks.added,
@@ -423,6 +426,7 @@ macro_rules! impl_methods {
             /// ```
             pub fn map_unchanged<U: ?Sized>(self, f: impl FnOnce(&mut $target) -> &mut U) -> Mut<'w, U> {
                 Mut {
+                    on_change: self.on_change,
                     value: f(self.value),
                     ticks: self.ticks,
                     #[cfg(feature = "track_change_detection")]
@@ -437,6 +441,7 @@ macro_rules! impl_methods {
             pub fn filter_map_unchanged<U: ?Sized>(self, f: impl FnOnce(&mut $target) -> Option<&mut U>) -> Option<Mut<'w, U>> {
                 let value = f(self.value);
                 value.map(|value| Mut {
+                    on_change: self.on_change,
                     value,
                     ticks: self.ticks,
                     #[cfg(feature = "track_change_detection")]
@@ -659,22 +664,31 @@ where
 
 change_detection_impl!(ResMut<'w, T>, T, Resource);
 change_detection_mut_impl!(ResMut<'w, T>, T, Resource);
-impl_methods!(ResMut<'w, T>, T, Resource);
+// impl_methods!(ResMut<'w, T>, T, Resource);
 impl_debug!(ResMut<'w, T>, Resource);
 
-impl<'w, T: Resource> From<ResMut<'w, T>> for Mut<'w, 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<'w, T>) -> Mut<'w, T> {
-        Mut {
-            value: other.value,
-            ticks: other.ticks,
-            #[cfg(feature = "track_change_detection")]
-            changed_by: other.changed_by,
-        }
+impl<'w, T: ?Sized + Resource>  ResMut<'w, T> {
+
+    /// TODO
+    pub fn into_inner(mut self) -> &'w mut T {
+        self.set_changed();
+        self.value
     }
 }
 
+// impl<'w, T: Resource> From<ResMut<'w, T>> for Mut<'w, 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<'w, T>) -> Mut<'w, T> {
+//         Mut {
+//             value: other.value,
+//             ticks: other.ticks,
+//             #[cfg(feature = "track_change_detection")]
+//             changed_by: other.changed_by,
+//         }
+//     }
+// }
+
 /// Unique borrow of a non-[`Send`] resource.
 ///
 /// Only [`Send`] resources may be accessed with the [`ResMut`] [`SystemParam`](crate::system::SystemParam). In case that the
@@ -695,21 +709,21 @@ pub struct NonSendMut<'w, T: ?Sized + 'static> {
 
 change_detection_impl!(NonSendMut<'w, T>, T,);
 change_detection_mut_impl!(NonSendMut<'w, T>, T,);
-impl_methods!(NonSendMut<'w, T>, T,);
+// impl_methods!(NonSendMut<'w, T>, T,);
 impl_debug!(NonSendMut<'w, T>,);
 
-impl<'w, T: 'static> From<NonSendMut<'w, T>> for Mut<'w, 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<'w, T>) -> Mut<'w, T> {
-        Mut {
-            value: other.value,
-            ticks: other.ticks,
-            #[cfg(feature = "track_change_detection")]
-            changed_by: other.changed_by,
-        }
-    }
-}
+// impl<'w, T: 'static> From<NonSendMut<'w, T>> for Mut<'w, 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<'w, T>) -> Mut<'w, T> {
+//         Mut {
+//             value: other.value,
+//             ticks: other.ticks,
+//             #[cfg(feature = "track_change_detection")]
+//             changed_by: other.changed_by,
+//         }
+//     }
+// }
 
 /// Shared borrow of an entity's component with access to change detection.
 /// Similar to [`Mut`] but is immutable and so doesn't require unique access.
@@ -869,6 +883,7 @@ impl_debug!(Ref<'w, T>,);
 /// # fn update_player_position(player: &Player, new_position: Position) {}
 /// ```
 pub struct Mut<'w, T: ?Sized> {
+    pub(crate) on_change: Option<(EntityChange, &'w RefCell<EntityChanges>)>,
     pub(crate) value: &'w mut T,
     pub(crate) ticks: TicksMut<'w>,
     #[cfg(feature = "track_change_detection")]
@@ -900,6 +915,7 @@ impl<'w, T: ?Sized> Mut<'w, T> {
         #[cfg(feature = "track_change_detection")] caller: &'w mut &'static Location<'static>,
     ) -> Self {
         Self {
+            on_change: None,
             value,
             ticks: TicksMut {
                 added,
@@ -949,8 +965,58 @@ where
     }
 }
 
+impl<'w, T: ?Sized> DetectChangesMut for Mut<'w, T> {
+    type Inner = T;
+    #[inline]
+    #[track_caller]
+    fn set_changed(&mut self) {
+        *self.ticks.changed = self.ticks.this_run;
+        if let Some((change, changes)) = self.on_change {
+            changes.borrow_mut().push(change);
+        }
+        #[cfg(feature = "track_change_detection")]
+        {
+            *self.changed_by = Location::caller();
+        }
+    }
+    #[inline]
+    #[track_caller]
+    fn set_last_changed(&mut self, last_changed: Tick) {
+        *self.ticks.changed = last_changed;
+        #[cfg(feature = "track_change_detection")]
+        {
+            *self.changed_by = Location::caller();
+        }
+    }
+
+    #[inline]
+    fn bypass_change_detection(&mut self) -> &mut Self::Inner {
+        self.value
+    }
+}
+
+impl<'w, T: ?Sized> DerefMut for Mut<'w, T> {
+    #[inline]
+    #[track_caller]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.set_changed();
+        #[cfg(feature = "track_change_detection")]
+        {
+            *self.changed_by = Location::caller();
+        }
+        self.value
+    }
+}
+
+impl<'w, T: ?Sized> AsMut<T> for Mut<'w, T> {
+    #[inline]
+    fn as_mut(&mut self) -> &mut T {
+        self.deref_mut()
+    }
+}
+
 change_detection_impl!(Mut<'w, T>, T,);
-change_detection_mut_impl!(Mut<'w, T>, T,);
+// change_detection_mut_impl!(Mut<'w, T>, T,);
 impl_methods!(Mut<'w, T>, T,);
 impl_debug!(Mut<'w, T>,);
 
@@ -1041,6 +1107,7 @@ impl<'w> MutUntyped<'w> {
     /// ```
     pub fn map_unchanged<T: ?Sized>(self, f: impl FnOnce(PtrMut<'w>) -> &'w mut T) -> Mut<'w, T> {
         Mut {
+            on_change: None, // TODO
             value: f(self.value),
             ticks: self.ticks,
             #[cfg(feature = "track_change_detection")]
@@ -1054,6 +1121,7 @@ impl<'w> MutUntyped<'w> {
     /// - `T` must be the erased pointee type for this [`MutUntyped`].
     pub unsafe fn with_type<T>(self) -> Mut<'w, T> {
         Mut {
+            on_change: None,
             // SAFETY: `value` is `Aligned` and caller ensures the pointee type is `T`.
             value: unsafe { self.value.deref_mut() },
             ticks: self.ticks,
@@ -1423,6 +1491,7 @@ mod tests {
         let mut caller = Location::caller();
 
         let ptr = Mut {
+            on_change: None,
             value: &mut outer,
             ticks,
             #[cfg(feature = "track_change_detection")]
@@ -1551,6 +1620,7 @@ mod tests {
         let mut caller = Location::caller();
 
         let mut_typed = Mut {
+            on_change: None,
             value: &mut c,
             ticks,
             #[cfg(feature = "track_change_detection")]

crates/bevy_ecs/src/observer/mod.rs

@@ -247,6 +247,7 @@ pub struct Observers {
     on_insert: CachedObservers,
     on_replace: CachedObservers,
     on_remove: CachedObservers,
+    on_mutate: CachedObservers,
     // Map from trigger type to set of observers
     cache: HashMap<ComponentId, CachedObservers>,
 }
@@ -258,6 +259,7 @@ impl Observers {
             ON_INSERT => &mut self.on_insert,
             ON_REPLACE => &mut self.on_replace,
             ON_REMOVE => &mut self.on_remove,
+            ON_MUTATE => &mut self.on_mutate,
             _ => self.cache.entry(event_type).or_default(),
         }
     }
@@ -268,6 +270,7 @@ impl Observers {
             ON_INSERT => Some(&self.on_insert),
             ON_REPLACE => Some(&self.on_replace),
             ON_REMOVE => Some(&self.on_remove),
+            ON_MUTATE => Some(&self.on_mutate),
             _ => self.cache.get(&event_type),
         }
     }
@@ -342,6 +345,7 @@ impl Observers {
             ON_INSERT => Some(ArchetypeFlags::ON_INSERT_OBSERVER),
             ON_REPLACE => Some(ArchetypeFlags::ON_REPLACE_OBSERVER),
             ON_REMOVE => Some(ArchetypeFlags::ON_REMOVE_OBSERVER),
+            ON_MUTATE => Some(ArchetypeFlags::ON_MUTATE_OBSERVER),
             _ => None,
         }
     }
@@ -378,6 +382,14 @@ impl Observers {
         {
             flags.insert(ArchetypeFlags::ON_REMOVE_OBSERVER);
         }
+
+        if self
+            .on_mutate
+            .component_observers
+            .contains_key(&component_id)
+        {
+            flags.insert(ArchetypeFlags::ON_MUTATE_OBSERVER);
+        }
     }
 }