Custom VecMap and VecSet collections for cache-friendly linear search

Does HashMap and HashSet already implement these optimizations?
Almost certainly...

engine/src/collections.rs

@@ -0,0 +1,124 @@
+/// A vec-backed set for cache-friendly queries
+#[derive(Debug)]
+pub struct VecSet<T: PartialEq> {
+    inner: Vec<Option<T>>
+}
+
+impl<T: PartialEq> VecSet<T> {
+    pub fn insert(&mut self, value: T) {
+        // Check if value already in set, otherwise add it
+        if !self.contains(&value) {
+            self.inner.push(Some(value))
+        }
+    }
+
+    pub fn remove(&mut self, value: &T) {
+        self.inner.iter_mut().for_each(|val| {
+            if val.as_ref() == Some(value) {
+                *val = None;
+            }
+        })
+    }
+
+    pub fn compact(&mut self) {
+        self.inner.retain(|val| val.is_some())
+    }
+
+    pub fn clear(&mut self) {
+        self.inner.clear();
+    }
+
+    pub fn contains(&self, value: &T) -> bool {
+        self.iter().any(|v| v == value)
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = &T> {
+        self.inner.iter().filter_map(|v| v.as_ref())
+    }
+}
+
+impl<T: PartialEq> FromIterator<T> for VecSet<T> {
+    fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> Self {
+        VecSet::<T> {
+            inner: iter.into_iter().map(|this| Some(this)).collect()
+        }
+    }
+}
+
+impl<T: PartialEq> Default for VecSet<T> {
+    fn default() -> Self {
+        VecSet { inner: Vec::new() }
+    }
+}
+
+/// A vec-backed map for cache-friendly queries
+#[derive(Debug)]
+pub struct VecMap<K: PartialEq, V> {
+    inner: Vec<Option<(K, V)>>
+}
+
+impl<K: PartialEq, V> VecMap<K, V> {
+    pub fn insert(&mut self, key: K, val: V) {
+        // Check and remove/overwrite existing entry
+        if let Some(v) = self.get_mut(&key) {
+            // Update value at key
+            *v = val;
+        } else {
+            self.inner.push(Some((key, val)));
+        }
+    }
+
+    pub fn get(&self, key: &K) -> Option<&V> {
+        self.iter().find_map(|(k, v)| (k == key).then_some(v))
+    }
+
+    pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
+        self.iter_mut().find_map(|(k, v)| (k == key).then_some(v))
+    }
+
+    pub fn remove(&mut self, key: &K) {
+        self.get_mut(key).take();
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = &(K,V)> {
+        self.inner.iter().filter_map(|kv| kv.as_ref())
+    }
+
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut (K,V)> {
+        self.inner.iter_mut().filter_map(|kv| kv.as_mut())
+    }
+
+    pub fn compact(&mut self) {
+        self.inner.retain(|v| v.is_some());
+    }
+
+    pub fn clear(&mut self) {
+        self.inner.clear();
+    }
+
+    pub fn keys(&self) -> impl Iterator<Item = &K> {
+        self.inner.iter().filter_map(|this| this.as_ref().map(|(k,_)| k))
+    }
+
+    pub fn contains_key(&self, key: &K) -> bool {
+        self.keys().any(|k| k == key)
+    }
+
+    pub fn values(&self) -> impl Iterator<Item = &V> {
+        self.inner.iter().filter_map(|this| this.as_ref().map(|(_,v)| v))
+    }
+}
+
+impl<K: PartialEq,V> FromIterator<(K,V)> for VecMap<K,V> {
+    fn from_iter<I: IntoIterator<Item=(K,V)>>(iter: I) -> Self {
+        VecMap::<K,V> {
+            inner: iter.into_iter().map(|this| Some(this)).collect()
+        }
+    }
+}
+
+impl<K: PartialEq, V> Default for VecMap<K, V> {
+    fn default() -> Self {
+        VecMap { inner: Vec::new() }
+    }
+}

engine/src/lib.rs

@@ -1,6 +1,11 @@
+/// Actions handler framework
 pub mod actions;
 pub use actions::*;
 
+/// Custom collections using Vec for cache-friendly queries
+pub mod collections;
+pub use collections::*;
+
 pub mod color;
 use bevy::ecs::query::QueryFilter;
 pub use color::*;

life/src/main.rs

@@ -820,10 +820,10 @@ enum SimulationPlayback {
 fn simulation_step(
     q: Query<(Entity, &Coordinates), With<Cell>>,
     mut writer: MessageWriter<Lifecycle>,
-    mut alive: Local<HashMap<Coordinates, Entity>>,
-    mut candidates: Local<HashSet<Coordinates>>,
+    mut alive: Local<VecMap<Coordinates, Entity>>,
+    mut candidates: Local<VecSet<Coordinates>>,
 ) {
-    let living_neighbors = |a: &HashMap<Coordinates, Entity>, c: &Coordinates| -> usize {
+    let living_neighbors = |a: &VecMap<Coordinates, Entity>, c: &Coordinates| -> usize {
         c.neighbors()
             .filter(|neighbor| {
                 a.contains_key(neighbor)
@@ -938,8 +938,8 @@ fn cooldown_secs(input: f32) -> impl FnMut(Local<Timer>, Res<Time>) -> bool + Cl
 
 #[derive(Resource, Default, Debug)]
 struct CellAssets {
-    pitches: HashMap<CellPitch, Handle<Pitch>>,
-    materials: HashMap<CellPitch, Handle<ColorMaterial>>,
+    pitches: VecMap<CellPitch, Handle<Pitch>>,
+    materials: VecMap<CellPitch, Handle<ColorMaterial>>,
     mesh: Handle<Mesh>,
 }
 
@@ -1077,7 +1077,7 @@ fn load_audio_tones(mut pitches: ResMut<Assets<Pitch>>, mut cell_assets: ResMut<
         });
         cell_assets.pitches.insert(cell_pitch, handle);
     });
-    debug_assert_eq!(cell_assets.pitches.iter().len(), 132);
+    debug_assert_eq!(cell_assets.pitches.iter().count(), 132);
 }
 
 fn load_materials(
@@ -1101,7 +1101,7 @@ fn load_materials(
         cell_assets.materials.insert(cell_pitch, handle);
     });
     // 12 notes * 11 octaves = 132 materials
-    debug_assert_eq!(cell_assets.materials.iter().len(), 132);
+    debug_assert_eq!(cell_assets.materials.iter().count(), 132);
 }
 
 fn load_meshes(mut cell_assets: ResMut<CellAssets>, mut meshes: ResMut<Assets<Mesh>>) {
@@ -1392,7 +1392,7 @@ fn manage_audio_players(
     cell_assets: Res<CellAssets>,
     pitch_map: Res<PitchMap>,
     current: Query<(Entity, &CellPitch), With<AudioSink>>,
-    mut active: Local<HashSet<CellPitch>>,
+    mut active: Local<VecSet<CellPitch>>,
 ) {
     *active = pitch_map.iter_enabled_cell_pitches().collect();
     CellPitch::iter_all().for_each(|cp| {
@@ -1420,7 +1420,7 @@ fn control_audio_players(
     simulation_state: Res<State<SimulationPlayback>>,
     mut players: Query<(&mut AudioSink, &CellPitch)>,
     cells: Query<&CellPitch, With<Cell>>,
-    mut active_cells: Local<HashMap<CellPitch, usize>>,
+    mut active_cells: Local<VecMap<CellPitch, usize>>,
 ) {
     fn turn_off(sink: &mut AudioSink) {
         if !sink.is_paused() {
@@ -1451,8 +1451,10 @@ fn control_audio_players(
                 SimulationPlayback::Run => {
                     // Count number of each type of cell for audio
                     cells.iter().for_each(|cp| {
-                        let this = active_cells.entry(cp.clone()).or_insert(0);
-                        *this += 1;
+                        match active_cells.get_mut(cp) {
+                            Some(v) => *v += 1,
+                            None => active_cells.insert(cp.clone(), 1),
+                        }
                     });
 
                     // Get the total to compute per-cell ratio