refactor(ecs)!: reworked the entity id system

crates/comet_app/src/app.rs

@@ -1,5 +1,7 @@
 use comet_colors::{Color as ColorTrait, LinearRgba};
-use comet_ecs::{Camera2D, Component, Entity, Render2D, Scene, Text, Transform2D, Transform3D};
+use comet_ecs::{
+    Camera2D, Component, Entity, EntityId, Render2D, Scene, Text, Transform2D, Transform3D,
+};
 use comet_input::keyboard::Key;
 use comet_log::*;
 use comet_renderer::renderer::Renderer;
@@ -163,22 +165,22 @@ impl App {
     }
 
     /// Creates a new entity and returns its ID.
-    pub fn new_entity(&mut self) -> usize {
+    pub fn new_entity(&mut self) -> EntityId {
-        self.scene.new_entity() as usize
+        self.scene.new_entity()
     }
 
     /// Deletes an entity by its ID.
-    pub fn delete_entity(&mut self, entity_id: usize) {
+    pub fn delete_entity(&mut self, entity_id: EntityId) {
         self.scene.delete_entity(entity_id)
     }
 
     /// Gets an immutable reference to an entity by its ID.
-    pub fn get_entity(&self, entity_id: usize) -> Option<&Entity> {
+    pub fn get_entity(&self, entity_id: EntityId) -> Option<&Entity> {
         self.scene.get_entity(entity_id)
     }
 
     /// Gets a mutable reference to an entity by its ID.
-    pub fn get_entity_mut(&mut self, entity_id: usize) -> Option<&mut Entity> {
+    pub fn get_entity_mut(&mut self, entity_id: EntityId) -> Option<&mut Entity> {
         self.scene.get_entity_mut(entity_id)
     }
 
@@ -194,29 +196,29 @@ impl App {
 
     /// Adds a component to an entity by its ID and an instance of the component.
     /// Overwrites the previous component if another component of the same type is added.
-    pub fn add_component<C: Component>(&mut self, entity_id: usize, component: C) {
+    pub fn add_component<C: Component>(&mut self, entity_id: EntityId, component: C) {
         self.scene.add_component(entity_id, component)
     }
 
     /// Removes a component from an entity by its ID.
-    pub fn remove_component<C: Component>(&mut self, entity_id: usize) {
+    pub fn remove_component<C: Component>(&mut self, entity_id: EntityId) {
         self.scene.remove_component::<C>(entity_id)
     }
 
     /// Returns a reference to a component of an entity by its ID.
-    pub fn get_component<C: Component>(&self, entity_id: usize) -> Option<&C> {
+    pub fn get_component<C: Component>(&self, entity_id: EntityId) -> Option<&C> {
         self.scene.get_component::<C>(entity_id)
     }
 
     /// Returns a mutable reference to a component of an entity by its ID.
-    pub fn get_component_mut<C: Component>(&mut self, entity_id: usize) -> Option<&mut C> {
+    pub fn get_component_mut<C: Component>(&mut self, entity_id: EntityId) -> Option<&mut C> {
         self.scene.get_component_mut::<C>(entity_id)
     }
 
     /// Returns a list of entities that have the given components.
     /// The amount of queriable components is limited to 3 such that the `Archetype` creation is more efficient.
     /// Otherwise it would be a factorial complexity chaos.
-    pub fn get_entities_with(&self, components: Vec<TypeId>) -> Vec<usize> {
+    pub fn get_entities_with(&self, components: Vec<TypeId>) -> Vec<EntityId> {
         self.scene.get_entities_with(components)
     }
 
@@ -233,7 +235,7 @@ impl App {
     }
 
     /// Returns whether an entity has the given component.
-    pub fn has<C: Component>(&self, entity_id: usize) -> bool {
+    pub fn has<C: Component>(&self, entity_id: EntityId) -> bool {
         self.scene.has::<C>(entity_id)
     }
 
@@ -243,7 +245,7 @@ impl App {
     }
 
     /// Spawns a prefab with the given name.
-    pub fn spawn_prefab(&mut self, name: &str) -> Option<usize> {
+    pub fn spawn_prefab(&mut self, name: &str) -> Option<EntityId> {
         self.scene.spawn_prefab(name)
     }
 

crates/comet_ecs/src/component.rs

@@ -436,13 +436,15 @@ impl Camera for Camera2D {
         let entities = scene.entities();
         let mut visible_entities = Vec::new();
         for entity in entities {
-            let id = *entity.clone().unwrap().id() as usize;
+            if let Some(ent) = entity.clone() {
+                let id = ent.id();
                 if let Some(transform) = scene.get_component::<Transform2D>(id) {
                     if self.in_view_frustum(camera_position, transform.position()) {
-                    visible_entities.push(entity.clone().unwrap());
+                        visible_entities.push(ent);
                     }
                 } else {
-                error!("Entity {} missing Transform2D", id);
+                    error!("Entity {} missing Transform2D", id.index);
+                }
             }
         }
         visible_entities

crates/comet_ecs/src/entity.rs

@@ -1,21 +1,35 @@
 use bit_set::BitSet;
 
+/// Handle used to reference entities safely. Contains an index into the entity
+/// storage and a generation counter to detect stale handles.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct EntityId {
+    pub index: u32,
+    pub gen: u32,
+}
+
+impl Default for EntityId {
+    fn default() -> Self {
+        Self { index: 0, gen: 0 }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct Entity {
-	id: u32,
+    id: EntityId,
-	components: BitSet
+    components: BitSet,
 }
 
 impl Entity {
-	pub(crate) fn new(id: u32) -> Self {
+    pub(crate) fn new(index: u32, gen: u32) -> Self {
         Self {
-			id,
+            id: EntityId { index, gen },
-			components: BitSet::new()
+            components: BitSet::new(),
         }
     }
 
-	pub fn id(&self) -> &u32 {
+    pub fn id(&self) -> EntityId {
-		&self.id
+        self.id
     }
 
     pub(crate) fn add_component(&mut self, component_index: usize) {

crates/comet_ecs/src/prefabs.rs

@@ -1,6 +1,6 @@
 use comet_structs::FlatMap;
 
-pub type PrefabFactory = fn(&mut crate::Scene) -> usize;
+pub type PrefabFactory = fn(&mut crate::Scene) -> crate::EntityId;
 
 pub(crate) struct PrefabManager {
     pub(crate) prefabs: FlatMap<String, PrefabFactory>,
@@ -26,8 +26,8 @@ impl PrefabManager {
 macro_rules! register_prefab {
     ($scene:expr, $name:expr, $($component:expr),* $(,)?) => {
         {
-            fn prefab_factory(scene: &mut $crate::Scene) -> usize {
+            fn prefab_factory(scene: &mut $crate::Scene) -> $crate::EntityId {
-                let entity = scene.new_entity() as usize;
+                let entity = scene.new_entity();
                 $(
                     scene.add_component(entity, $component);
                 )*

crates/comet_ecs/src/scene.rs

@@ -1,6 +1,6 @@
 use crate::archetypes::Archetypes;
 use crate::prefabs::PrefabManager;
-use crate::{Component, Entity, IdQueue};
+use crate::{Component, Entity, EntityId, IdQueue};
 use comet_log::*;
 use comet_structs::*;
 use std::any::TypeId;
@@ -8,6 +8,7 @@ use std::any::TypeId;
 pub struct Scene {
     id_queue: IdQueue,
     next_id: u32,
+    generations: Vec<u32>,
     entities: Vec<Option<Entity>>,
     components: ComponentStorage,
     archetypes: Archetypes,
@@ -19,6 +20,7 @@ impl Scene {
         Self {
             id_queue: IdQueue::new(),
             next_id: 0,
+            generations: Vec::new(),
             entities: Vec::new(),
             components: ComponentStorage::new(),
             archetypes: Archetypes::new(),
@@ -43,45 +45,80 @@ impl Scene {
         }
     }
 
+    fn is_alive(&self, id: EntityId) -> bool {
+        self.generations
+            .get(id.index as usize)
+            .is_some_and(|g| *g == id.gen)
+            && self
+                .entities
+                .get(id.index as usize)
+                .is_some_and(|e| e.is_some())
+    }
+
     /// Retuns the `Vec` of `Option<Entity>` which contains all the entities in the current Scene.
     pub fn entities(&self) -> &Vec<Option<Entity>> {
         &self.entities
     }
 
     /// Creates a new entity and returns its ID.
-    pub fn new_entity(&mut self) -> u32 {
+    pub fn new_entity(&mut self) -> EntityId {
-        let id = self.next_id;
+        let index = self.next_id;
-        if (self.next_id as usize) >= self.entities.len() {
+        let gen = if (index as usize) >= self.generations.len() {
-            self.entities.push(Some(Entity::new(self.next_id)));
+            self.generations.push(0);
-            self.get_next_id();
+            0
-            info!("Created entity! ID: {}", id);
+        } else {
-            return id;
+            self.generations[index as usize]
+        };
+
+        if (index as usize) >= self.entities.len() {
+            self.entities.push(Some(Entity::new(index, gen)));
+        } else {
+            self.entities[index as usize] = Some(Entity::new(index, gen));
         }
-        self.entities[self.next_id as usize] = Some(Entity::new(self.next_id));
+
+        let id = EntityId { index, gen };
         self.get_next_id();
-        info!("Created entity! ID: {}", id);
+        info!("Created entity! ID: {} (gen {})", id.index, id.gen);
         id
     }
 
     /// Gets an immutable reference to an entity by its ID.
-    pub fn get_entity(&self, entity_id: usize) -> Option<&Entity> {
+    pub fn get_entity(&self, entity_id: EntityId) -> Option<&Entity> {
-        self.entities.get(entity_id).and_then(|e| e.as_ref())
+        if !self.is_alive(entity_id) {
+            return None;
+        }
+        self.entities
+            .get(entity_id.index as usize)
+            .and_then(|e| e.as_ref())
     }
 
     /// Gets a mutable reference to an entity by its ID.
-    pub fn get_entity_mut(&mut self, entity_id: usize) -> Option<&mut Entity> {
+    pub fn get_entity_mut(&mut self, entity_id: EntityId) -> Option<&mut Entity> {
-        self.entities.get_mut(entity_id).and_then(|e| e.as_mut())
+        if !self.is_alive(entity_id) {
+            return None;
+        }
+        self.entities
+            .get_mut(entity_id.index as usize)
+            .and_then(|e| e.as_mut())
     }
 
     /// Deletes an entity by its ID.
-    pub fn delete_entity(&mut self, entity_id: usize) {
+    pub fn delete_entity(&mut self, entity_id: EntityId) {
-        self.remove_entity_from_archetype(entity_id as u32, self.get_component_set(entity_id));
+        if !self.is_alive(entity_id) {
-        self.entities[entity_id] = None;
+            return;
-        info!("Deleted entity! ID: {}", entity_id);
-        for (_, value) in self.components.iter_mut() {
-            value.remove::<u8>(entity_id);
         }
-        self.id_queue.sorted_enqueue(entity_id as u32);
+
+        let idx = entity_id.index as usize;
+        self.remove_entity_from_archetype(entity_id.index, self.get_component_set(idx));
+        self.entities[idx] = None;
+        info!("Deleted entity! ID: {}", entity_id.index);
+        for (_, value) in self.components.iter_mut() {
+            value.remove::<u8>(idx);
+        }
+        if let Some(gen) = self.generations.get_mut(idx) {
+            *gen = gen.wrapping_add(1);
+        }
+        self.id_queue.sorted_enqueue(entity_id.index);
         self.get_next_id();
     }
 
@@ -159,13 +196,23 @@ impl Scene {
 
     /// Adds a component to an entity by its ID and an instance of the component.
     /// Overwrites the previous component if another component of the same type is added.
-    pub fn add_component<C: Component + 'static>(&mut self, entity_id: usize, component: C) {
+    pub fn add_component<C: Component + 'static>(&mut self, entity_id: EntityId, component: C) {
-        let old_component_set = self.get_component_set(entity_id);
+        if !self.is_alive(entity_id) {
-        if !old_component_set.to_vec().is_empty() {
+            error!(
-            self.remove_entity_from_archetype(entity_id as u32, old_component_set);
+                "Attempted to add component {} to dead entity {}",
+                C::type_name(),
+                entity_id.index
+            );
+            return;
         }
 
-        self.components.set_component(entity_id, component);
+        let old_component_set = self.get_component_set(entity_id.index as usize);
+        if !old_component_set.to_vec().is_empty() {
+            self.remove_entity_from_archetype(entity_id.index, old_component_set);
+        }
+
+        self.components
+            .set_component(entity_id.index as usize, component);
         if let Some(component_index) = self
             .components
             .keys()
@@ -175,36 +222,43 @@ impl Scene {
             if let Some(entity) = self.get_entity_mut(entity_id) {
                 entity.add_component(component_index);
             } else {
-                error!("Attempted to add component to non-existent entity {}", entity_id);
+                error!(
+                    "Attempted to add component to non-existent entity {}",
+                    entity_id.index
+                );
             }
         } else {
             error!(
                 "Component {} not registered, cannot add to entity {}",
                 C::type_name(),
-                entity_id
+                entity_id.index
             );
         }
 
-        let new_component_set = self.get_component_set(entity_id);
+        let new_component_set = self.get_component_set(entity_id.index as usize);
 
         if !self.archetypes.contains_archetype(&new_component_set) {
             self.create_archetype(new_component_set.clone());
         }
 
-        self.add_entity_to_archetype(entity_id as u32, new_component_set);
+        self.add_entity_to_archetype(entity_id.index, new_component_set);
 
         info!(
             "Added component {} to entity {}!",
             C::type_name(),
-            entity_id
+            entity_id.index
         );
     }
 
-    pub fn remove_component<C: Component + 'static>(&mut self, entity_id: usize) {
+    pub fn remove_component<C: Component + 'static>(&mut self, entity_id: EntityId) {
-        let old_component_set = self.get_component_set(entity_id);
+        if !self.is_alive(entity_id) {
-        self.remove_entity_from_archetype(entity_id as u32, old_component_set);
+            return;
+        }
+        let old_component_set = self.get_component_set(entity_id.index as usize);
+        self.remove_entity_from_archetype(entity_id.index, old_component_set);
 
-        self.components.remove_component::<C>(entity_id);
+        self.components
+            .remove_component::<C>(entity_id.index as usize);
         if let Some(component_index) = self
             .components
             .keys()
@@ -216,48 +270,73 @@ impl Scene {
             }
         }
 
-        let new_component_set = self.get_component_set(entity_id);
+        let new_component_set = self.get_component_set(entity_id.index as usize);
 
         if !new_component_set.to_vec().is_empty() {
             if !self.archetypes.contains_archetype(&new_component_set) {
                 self.create_archetype(new_component_set.clone());
             }
 
-            self.add_entity_to_archetype(entity_id as u32, new_component_set);
+            self.add_entity_to_archetype(entity_id.index, new_component_set);
         }
 
         info!(
             "Removed component {} from entity {}!",
             C::type_name(),
-            entity_id
+            entity_id.index
         );
     }
 
     /// Returns a reference to a component of an entity by its ID.
-    pub fn get_component<C: Component + 'static>(&self, entity_id: usize) -> Option<&C> {
+    pub fn get_component<C: Component + 'static>(&self, entity_id: EntityId) -> Option<&C> {
-        self.components.get_component::<C>(entity_id)
+        if !self.is_alive(entity_id) {
+            return None;
+        }
+        self.components
+            .get_component::<C>(entity_id.index as usize)
     }
 
     pub fn get_component_mut<C: Component + 'static>(
         &mut self,
-        entity_id: usize,
+        entity_id: EntityId,
     ) -> Option<&mut C> {
-        self.components.get_component_mut::<C>(entity_id)
+        if !self.is_alive(entity_id) {
+            return None;
+        }
+        self.components
+            .get_component_mut::<C>(entity_id.index as usize)
     }
 
-    pub fn has<C: Component + 'static>(&self, entity_id: usize) -> bool {
+    pub fn has<C: Component + 'static>(&self, entity_id: EntityId) -> bool {
-        self.components.get_component::<C>(entity_id).is_some()
+        self.is_alive(entity_id)
+            && self
+                .components
+                .get_component::<C>(entity_id.index as usize)
+                .is_some()
     }
 
     /// Returns a list of entities that have the given components.
-    pub fn get_entities_with(&self, components: Vec<TypeId>) -> Vec<usize> {
+    pub fn get_entities_with(&self, components: Vec<TypeId>) -> Vec<EntityId> {
         let component_set = ComponentSet::from_ids(components);
         let mut result = Vec::new();
 
         for archetype_set in self.archetypes.component_sets() {
             if component_set.is_subset(&archetype_set) {
                 if let Some(entities) = self.archetypes.get_archetype(&archetype_set) {
-                    result.extend(entities.iter().map(|x| *x as usize));
+                    for index in entities.iter() {
+                        if let Some(gen) = self.generations.get(*index as usize) {
+                            if self
+                                .entities
+                                .get(*index as usize)
+                                .is_some_and(|e| e.is_some())
+                            {
+                                result.push(EntityId {
+                                    index: *index,
+                                    gen: *gen,
+                                });
+                            }
+                        }
+                    }
                 }
             }
         }
@@ -286,8 +365,9 @@ impl Scene {
                 .components
                 .get_two_mut(&C::type_id(), &K::type_id());
 
-            let c_opt = c_set.and_then(|set| set.get_mut::<C>(entity));
+            let idx = entity.index as usize;
-            let k_opt = k_set.and_then(|set| set.get_mut::<K>(entity));
+            let c_opt = c_set.and_then(|set| set.get_mut::<C>(idx));
+            let k_opt = k_set.and_then(|set| set.get_mut::<K>(idx));
 
             if let (Some(c), Some(k)) = (c_opt, k_opt) {
                 func(c, k);
@@ -301,7 +381,7 @@ impl Scene {
     }
 
     /// Spawns a prefab with the given name.
-    pub fn spawn_prefab(&mut self, name: &str) -> Option<usize> {
+    pub fn spawn_prefab(&mut self, name: &str) -> Option<EntityId> {
         if self.prefabs.has_prefab(name) {
             if let Some(factory) = self.prefabs.prefabs.get(&name.to_string()) {
                 let factory = *factory; // Copy the function pointer

crates/comet_renderer/src/camera.rs

@@ -18,7 +18,11 @@ impl CameraManager {
         self.cameras.get(self.active_camera).unwrap()
     }
 
-    pub fn update_from_scene(&mut self, scene: &comet_ecs::Scene, camera_entities: Vec<usize>) {
+    pub fn update_from_scene(
+        &mut self,
+        scene: &comet_ecs::Scene,
+        camera_entities: Vec<comet_ecs::EntityId>,
+    ) {
         self.cameras.clear();
 
         let mut cameras_with_priority: Vec<(RenderCamera, u8)> = Vec::new();

crates/comet_renderer/src/renderer2d.rs

@@ -62,7 +62,7 @@ pub struct Renderer2D<'a> {
     resource_manager: GraphicResourceManager,
     camera_manager: CameraManager,
     render_passes: Vec<RenderPass>,
-    cached_render_entities: Vec<usize>,
+    cached_render_entities: Vec<comet_ecs::EntityId>,
     last_frame_time: std::time::Instant,
     delta_time: f32,
 }
@@ -754,7 +754,8 @@ impl<'a> Renderer2D<'a> {
         let mut dirty_sort = self.cached_render_entities.len() != unsorted_entities.len();
 
         if !dirty_sort {
-            let unsorted_set: HashSet<usize> = unsorted_entities.iter().copied().collect();
+            let unsorted_set: HashSet<comet_ecs::EntityId> =
+                unsorted_entities.iter().copied().collect();
             dirty_sort = self
                 .cached_render_entities
                 .iter()
@@ -952,7 +953,7 @@ impl<'a> Renderer2D<'a> {
         }
     }
 
-    fn setup_camera(&mut self, scene: &comet_ecs::Scene, cameras: Vec<usize>) {
+    fn setup_camera(&mut self, scene: &comet_ecs::Scene, cameras: Vec<comet_ecs::EntityId>) {
         if cameras.is_empty() {
             return;
         }