entity thawing and freezing on level change

src/components.rs

@@ -23,6 +23,13 @@ pub struct Position {
     pub y: i32,
 }
 
+#[derive(Component, Serialize, Deserialize, Clone)]
+pub struct OtherLevelPosition {
+    pub x: i32,
+    pub y: i32,
+    pub id: i32,
+}
+
 #[derive(Component, ConvertSaveload, Clone)]
 pub struct Renderable {
     pub glyph: rltk::FontCharType,

src/main.rs

@@ -85,6 +85,8 @@ impl State {
         let map_building_info = map::level_transition(&mut self.ecs, new_id, offset);
         if let Some(history) = map_building_info {
             self.mapgen_history = history;
+        } else {
+            map::dungeon::thaw_entities(&mut self.ecs);
         }
     }
 
@@ -133,58 +135,9 @@ impl State {
         mapindex.run_now(&self.ecs);
     }
 
-    fn entities_to_remove_on_level_change(&mut self) -> Vec<Entity> {
-        let entities = self.ecs.entities();
-        let player = self.ecs.read_storage::<Player>();
-        let clock = self.ecs.read_storage::<Clock>();
-        let backpack = self.ecs.read_storage::<InBackpack>();
-        let player_entity = self.ecs.fetch::<Entity>();
-        let equipped = self.ecs.read_storage::<Equipped>();
-
-        let mut to_delete: Vec<Entity> = Vec::new();
-        for entity in entities.join() {
-            let mut should_delete = true;
-
-            // Don't delete the turn clock
-            let c = clock.get(entity);
-            if let Some(_c) = c {
-                should_delete = false;
-            }
-
-            // Don't delete player
-            let p = player.get(entity);
-            if let Some(_p) = p {
-                should_delete = false;
-            }
-
-            // Don't delete player's equipment
-            let bp = backpack.get(entity);
-            if let Some(bp) = bp {
-                if bp.owner == *player_entity {
-                    should_delete = false;
-                }
-            }
-            let eq = equipped.get(entity);
-            if let Some(eq) = eq {
-                if eq.owner == *player_entity {
-                    should_delete = false;
-                }
-            }
-
-            if should_delete {
-                to_delete.push(entity);
-            }
-        }
-
-        return to_delete;
-    }
-
     fn goto_level(&mut self, offset: i32) {
-        // Delete entities that aren't player/player's equipment
-        let to_delete = self.entities_to_remove_on_level_change();
-        for target in to_delete {
-            self.ecs.delete_entity(target).expect("Unable to delete entity");
-        }
+        // Freeze the current level
+        map::dungeon::freeze_entities(&mut self.ecs);
 
         // Build new map + place player
         let current_id;
@@ -511,6 +464,7 @@ fn main() -> rltk::BError {
     };
 
     gs.ecs.register::<Position>();
+    gs.ecs.register::<OtherLevelPosition>();
     gs.ecs.register::<Renderable>();
     gs.ecs.register::<Prop>();
     gs.ecs.register::<Player>();

src/map/dungeon.rs

@@ -1,5 +1,5 @@
 use super::{Map, TileType};
-use crate::{gamelog, map_builders, Position, Telepath, Viewshed};
+use crate::{gamelog, map_builders, OtherLevelPosition, Position, Telepath, Viewshed};
 use rltk::prelude::*;
 use serde::{Deserialize, Serialize};
 use specs::prelude::*;
@@ -131,3 +131,49 @@ fn transition_to_new_map(ecs: &mut World, new_id: i32) -> Vec<Map> {
     dungeon_master.store_map(&builder.build_data.map);
     return mapgen_history;
 }
+
+/// Iterate through entities on the current level, save the current position and floor
+/// of each entity-to-be-frozen, and then delete their current position.
+pub fn freeze_entities(ecs: &mut World) {
+    // Obtain reqs from ECS
+    let entities = ecs.entities();
+    let mut positions = ecs.write_storage::<Position>();
+    let mut other_positions = ecs.write_storage::<OtherLevelPosition>();
+    let player_entity = ecs.fetch::<Entity>();
+    let map_id = ecs.fetch::<Map>().id;
+    // Save Positions and mark for deletion
+    let mut pos_to_delete: Vec<Entity> = Vec::new();
+    for (entity, pos) in (&entities, &positions).join() {
+        if entity != *player_entity {
+            other_positions
+                .insert(entity, OtherLevelPosition { x: pos.x, y: pos.y, id: map_id })
+                .expect("Failed to insert OtherLevelPosition");
+            pos_to_delete.push(entity);
+        }
+    }
+    for p in pos_to_delete.iter() {
+        positions.remove(*p);
+    }
+}
+
+/// Iterate through entities, and insert a Position component if the
+/// entity has an OtherLevelPosition for the new map id.
+pub fn thaw_entities(ecs: &mut World) {
+    // Obtain reqs from ECS
+    let entities = ecs.entities();
+    let mut positions = ecs.write_storage::<Position>();
+    let mut other_positions = ecs.write_storage::<OtherLevelPosition>();
+    let player_entity = ecs.fetch::<Entity>();
+    let map_id = ecs.fetch::<Map>().id;
+    // Save Positions and mark for deletion
+    let mut pos_to_delete: Vec<Entity> = Vec::new();
+    for (entity, pos) in (&entities, &other_positions).join() {
+        if entity != *player_entity && pos.id == map_id {
+            positions.insert(entity, Position { x: pos.x, y: pos.y }).expect("Failed to insert OtherLevelPosition");
+            pos_to_delete.push(entity);
+        }
+    }
+    for p in pos_to_delete.iter() {
+        other_positions.remove(*p);
+    }
+}

src/saveload_system.rs

@@ -79,6 +79,7 @@ pub fn save_game(ecs: &mut World) {
             MultiAttack,
             NaturalAttacks,
             Name,
+            OtherLevelPosition,
             ParticleLifetime,
             Player,
             Pools,
@@ -186,6 +187,7 @@ pub fn load_game(ecs: &mut World) {
             MultiAttack,
             NaturalAttacks,
             Name,
+            OtherLevelPosition,
             ParticleLifetime,
             Player,
             Pools,