feat: implement generic optimized collision system

src/systems/collision.rs

@@ -0,0 +1,47 @@
+use bevy_ecs::entity::Entity;
+use bevy_ecs::event::EventWriter;
+use bevy_ecs::query::With;
+use bevy_ecs::system::{Query, Res};
+
+use crate::error::GameError;
+use crate::events::GameEvent;
+use crate::map::builder::Map;
+use crate::systems::components::{Collider, ItemCollider, PacmanCollider, Position};
+
+pub fn collision_system(
+    map: Res<Map>,
+    pacman_query: Query<(Entity, &Position, &Collider), With<PacmanCollider>>,
+    item_query: Query<(Entity, &Position, &Collider), With<ItemCollider>>,
+    mut events: EventWriter<GameEvent>,
+    mut errors: EventWriter<GameError>,
+) {
+    // Check PACMAN × ITEM collisions
+    for (pacman_entity, pacman_pos, pacman_collider) in pacman_query.iter() {
+        for (item_entity, item_pos, item_collider) in item_query.iter() {
+            match (pacman_pos.get_pixel_pos(&map.graph), item_pos.get_pixel_pos(&map.graph)) {
+                (Ok(pacman_pixel), Ok(item_pixel)) => {
+                    // Calculate the distance between the two entities's precise pixel positions
+                    let distance = pacman_pixel.distance(item_pixel);
+                    // Calculate the distance at which the two entities will collide
+                    let collision_distance = (pacman_collider.size + item_collider.size) / 2.0;
+
+                    // If the distance between the two entities is less than the collision distance, then the two entities are colliding
+                    if distance < collision_distance {
+                        events.write(GameEvent::Collision(pacman_entity, item_entity));
+                    }
+                }
+                // Either or both of the pixel positions failed to get, so we need to report the error
+                (result_a, result_b) => {
+                    for result in [result_a, result_b] {
+                        if let Err(e) = result {
+                            errors.write(GameError::InvalidState(format!(
+                                "Collision system failed to get pixel positions for entities {:?} and {:?}: {}",
+                                pacman_entity, item_entity, e
+                            )));
+                        }
+                    }
+                }
+            }
+        }
+    }
+}