When sync_me is false avoid:

* Logging a warning when deleting the entity and it is not in any
  Region.
* Searching every single region for an entity that is in none of them.

Also:
* Add workaround for bug in specs where deleting any entity clears the
  components before checking that the generation is correct (surprised
  that we haven't encounted bugs from this yet).
* Properly update `tracked_entities` inside `RegionMap` when deleting
  an entity. Previously, we just relied on this being updated in
  `RegionMap::tick` by the absence of the `Pos` component at that index.
  However, this means if a new entity is created at that index after
  deletion and before calling `RegionMap::tick`, then this can be
  interpreted as an entity moving between regions rather than one being
  deleted and another created. It seems like this could lead to
  synchronization bugs like not creating the new entity on the client
  (although I haven't noticed this before, I think maybe we use newly
  inserted `Uid`s to detect new entities rather than the region system?).
  I think it could at least lead to sending redundant messages to
  synchronize the new entity.

client/src/lib.rs

@@ -2257,17 +2257,10 @@ impl Client {
                     .apply_entity_sync_package(entity_sync_package, uid);
             },
             ServerGeneral::CompSync(comp_sync_package, force_counter) => {
-                // TODO: Test with and without sync_me = true commented out to see if results are
-                // as expected. (client shouldn't normally receive updates if client physics is
-                // enabled)
-                let b = self.position();
                 self.force_update_counter = force_counter;
                 self.state
                     .ecs_mut()
                     .apply_comp_sync_package(comp_sync_package);
-                if b != self.position() {
-                    println!("{b:?}");
-                }
             },
             ServerGeneral::CreateEntity(entity_package) => {
                 self.state.ecs_mut().apply_entity_package(entity_package);

common/src/region.rs

@@ -209,6 +209,13 @@ impl RegionMap {
         }
     }
 
+    /// Must be called immediately after succesfully deleting an entity from the
+    /// ecs (i.e. when deleting the entity did not generate a WrongGeneration
+    /// error).
+    pub fn entity_deleted(&mut self, entity: specs::Entity) {
+        self.tracked_entities.remove(entity.id());
+    }
+
     fn add_entity(&mut self, id: u32, pos: Vec3<i32>, from: Option<Vec2<i32>>) {
         let key = Self::pos_key(pos);
         if let Some(region) = self.regions.get_mut(&key) {
@@ -247,6 +254,8 @@ impl RegionMap {
                     }
                 }
             }
+        } else if !self.tracked_entities.contains(id) {
+            return None;
         } else {
             // Check neighbors
             for o in &NEIGHBOR_OFFSETS {
@@ -269,26 +278,9 @@ impl RegionMap {
         None
     }
 
-    /// Checks if this entity is located in the `RegionMap` using the provided
-    /// position to limit which regions are checked.
-    ///
-    /// May produce false negatives (e.g. if for some reason the entity is not
-    /// in a region near the provided position).
-    pub fn in_region_map_relaxed(&self, entity: specs::Entity, pos: Vec3<f32>) -> bool {
-        let id = entity.id();
-        let pos = pos.map(|e| e as i32);
-
-        // Compute key for most likely region
-        let key = Self::pos_key(pos);
-        if let Some(region) = self.regions.get(&key) && region.entities().contains(id) { return true }
-
-        // Get the base of the four nearest regions.
-        let quad_base = Self::pos_key(pos - (REGION_SIZE / 2) as i32);
-        [(0, 0), (0, 1), (1, 0), (1, 1)]
-            .iter()
-            .map(|&offset| Vec2::<i32>::from(offset) + quad_base)
-            // skip key we already checked
-            .any(|k| k != key && self.regions.get(&key).is_some_and(|r| r.entities().contains(id)))
+    /// Checks if this entity is located in the `RegionMap`.
+    pub fn in_region_map(&self, entity: specs::Entity) -> bool {
+        self.tracked_entities.contains(entity.id())
     }
 
     fn key_index(&self, key: Vec2<i32>) -> Option<usize> {

server/src/events/player.rs

@@ -127,15 +127,16 @@ pub fn handle_exit_ingame(server: &mut Server, entity: EcsEntity, skip_persisten
         error!("handle_exit_ingame called with entity that is missing expected components");
     }
 
-    let maybe_character = state
+    let (maybe_character, sync_me) = state
         .read_storage::<Presence>()
         .get(entity)
-        .and_then(|p| p.kind.character_id());
+        .map(|p| (p.kind.character_id(), p.sync_me))
+        .unzip();
     let maybe_rtsim = state.read_component_copied::<common::rtsim::RtSimEntity>(entity);
     state.mut_resource::<IdMaps>().remove_entity(
         Some(entity),
         None, // Uid re-mapped, we don't want to remove the mapping
-        maybe_character,
+        maybe_character.flatten(),
         maybe_rtsim,
     );
 
@@ -143,7 +144,9 @@ pub fn handle_exit_ingame(server: &mut Server, entity: EcsEntity, skip_persisten
     // Uid to a new entity (and e.g. don't want it to be unmapped).
     //
     // Delete old entity
-    if let Err(e) = crate::state_ext::delete_entity_common(state, entity, maybe_uid) {
+    if let Err(e) =
+        crate::state_ext::delete_entity_common(state, entity, maybe_uid, sync_me.unwrap_or(true))
+    {
         error!(
             ?e,
             ?entity,

server/src/state_ext.rs

@@ -709,7 +709,7 @@ impl StateExt for State {
                         self.ecs()
                             .write_resource::<IdMaps>()
                             .add_character(id, entity);
-                        //presence.sync_me = true;
+                        presence.sync_me = true;
                         Ok(())
                     } else {
                         Err("PresenceKind is not LoadingCharacter")
@@ -1196,20 +1196,21 @@ impl StateExt for State {
         // NOTE: We expect that these 3 components are never removed from an entity (nor
         // mutated) (at least not without updating the relevant mappings)!
         let maybe_uid = self.read_component_copied::<Uid>(entity);
-        let maybe_character = self
+        let (maybe_character, sync_me) = self
             .read_storage::<Presence>()
             .get(entity)
-            .and_then(|p| p.kind.character_id());
+            .map(|p| (p.kind.character_id(), p.sync_me))
+            .unzip();
         let maybe_rtsim = self.read_component_copied::<RtSimEntity>(entity);
 
         self.mut_resource::<IdMaps>().remove_entity(
             Some(entity),
             maybe_uid,
-            maybe_character,
+            maybe_character.flatten(),
             maybe_rtsim,
         );
 
-        delete_entity_common(self, entity, maybe_uid)
+        delete_entity_common(self, entity, maybe_uid, sync_me.unwrap_or(true))
     }
 
     fn entity_as_actor(&self, entity: EcsEntity) -> Option<Actor> {
@@ -1247,6 +1248,7 @@ pub(crate) fn delete_entity_common(
     state: &mut State,
     entity: EcsEntity,
     maybe_uid: Option<Uid>,
+    sync_me: bool,
 ) -> Result<(), specs::error::WrongGeneration> {
     if maybe_uid.is_none() {
         // For now we expect all entities have a Uid component.
@@ -1254,8 +1256,24 @@ pub(crate) fn delete_entity_common(
     }
     let maybe_pos = state.read_component_copied::<comp::Pos>(entity);
 
-    let res = state.ecs_mut().delete_entity(entity);
+    // TODO: workaround for https://github.com/amethyst/specs/pull/766
+    let actual_gen = state.ecs().entities().entity(entity.id()).gen();
+    let res = if actual_gen == entity.gen() {
+        state.ecs_mut().delete_entity(entity)
+    } else {
+        Err(specs::error::WrongGeneration {
+            action: "delete",
+            actual_gen,
+            entity,
+        })
+    };
+
     if res.is_ok() {
+        let region_map = state.mut_resource::<common::region::RegionMap>();
+        let uid_pos_region_key = maybe_uid
+            .zip(maybe_pos)
+            .map(|(uid, pos)| (uid, pos, region_map.find_region(entity, pos.0)));
+        region_map.entity_deleted(entity);
         // Note: Adding the `Uid` to the deleted list when exiting "in-game" relies on
         // the client not being able to immediately re-enter the game in the
         // same tick (since we could then mix up the ordering of things and
@@ -1263,16 +1281,14 @@ pub(crate) fn delete_entity_common(
         //
         // The client will ignore requests to delete its own entity that are triggered
         // by this.
-        if let Some((uid, pos)) = maybe_uid.zip(maybe_pos) {
-            let region_key = state
-                .ecs()
-                .read_resource::<common::region::RegionMap>()
-                .find_region(entity, pos.0);
+        if let Some((uid, pos, region_key)) = uid_pos_region_key {
             if let Some(region_key) = region_key {
                 state
                     .mut_resource::<DeletedEntities>()
                     .record_deleted_entity(uid, region_key);
-            } else {
+            // If there is a position and sync_me is true, but the entity is not
+            // in a region, something might be wrong.
+            } else if sync_me {
                 // Don't panic if the entity wasn't found in a region, maybe it was just created
                 // and then deleted before the region manager had a chance to assign it a region
                 warn!(

server/src/sys/entity_sync.rs

@@ -325,8 +325,7 @@ impl<'a> System<'a> for Sys {
             // Include additional components for clients that aren't in a region (e.g. due
             // to having no position or have sync_me as `false`) since those
             // won't be synced above.
-            let include_all_comps =
-                !maybe_pos.is_some_and(|pos| region_map.in_region_map_relaxed(entity, pos.0));
+            let include_all_comps = region_map.in_region_map(entity);
 
             let mut comp_sync_package = trackers.create_sync_from_client_package(
                 &tracked_storages,