fix: randomised target positions

src/game/level/target_wall.rs

@@ -1,4 +1,6 @@
 
+use std::collections::HashMap;
+
 use bevy::prelude::*;
 use avian3d::prelude::*;
 
@@ -20,35 +22,90 @@ impl Plugin for TargetWallPlugin
 {
     fn build(&self, app: &mut App)
     {
+        app.insert_resource(TargetResources {
+            target_separation: 0.1,
+            target_handle_counter: 0,
+            targets: HashMap::new(),
+        });
+
         app.add_systems(Startup, setup_target_wall);
         app.add_systems(PostProcessCollisions, on_targets_shot.run_if(on_event::<CollisionEnded>));
     }
 }
 
-#[derive(Component)]
-struct Target;
+#[derive(Component, Copy, Clone, PartialEq, Eq, Hash)]
+struct TargetHandle(i32); // todo: would be nice to use the Entity handle here
 
-impl Target
+#[derive(Resource)]
+struct TargetResources
 {
-    fn random_transform() -> Transform
+    target_separation: f32,
+    target_handle_counter: i32,
+    targets: HashMap<TargetHandle,(Vec2,Circle)>,
+}
+
+impl TargetResources
+{
+    fn new_handle(&mut self) -> TargetHandle
+    {
+        self.target_handle_counter += 1;
+        TargetHandle(self.target_handle_counter)
+    }
+
+    fn random_transform(&mut self, handle: &TargetHandle) -> Transform
+    {
+        self.targets.remove(&handle);
+
+        let (transform, cache_entry) = loop
         {
             let radius = rand::random::<f32>() * 0.4 + 0.3;
             let x = rand::random::<f32>() * (WALL_SIZE.x - radius) - WALL_SIZE.x * 0.5;
-        let y = rand::random::<f32>() * (WALL_SIZE.y - radius);
+            let y = rand::random::<f32>() * (WALL_SIZE.y - radius) - WALL_SIZE.y * 0.5;
 
-        Transform::IDENTITY
-            .with_translation(Vec3::new(x, y, WALL_FACE_Z + TARGET_HEIGHT * 0.5))
+            let position = Vec2::new(x, y);
+            let circle = Circle::new(radius);
+
+            let has_overlap = self.targets.values().any(|&(position_other, circle_other)|
+            {
+                let distance_squared = Vec2::distance_squared(position, position_other);
+                let max_distance = circle.radius + circle_other.radius + self.target_separation;
+                distance_squared < max_distance * max_distance
+            });
+
+            if has_overlap {
+                continue;
+            }
+
+            let transform = Transform::IDENTITY
+                .with_translation(Vec3::new(x, y, TARGET_HEIGHT * 0.5))
                 .with_rotation(Quat::from_rotation_x(std::f32::consts::PI * 0.5))
                 .with_scale(Vec3::new(radius, 1.0, radius))
+                ;
+
+            break (transform, (position, circle));
+        };
+
+        self.targets.insert(*handle, cache_entry);
+        return transform;
     }
 }
 
+#[derive(Component)]
+pub struct TargetWall;
+
+#[derive(Component)]
+pub struct Target;
+
 fn setup_target_wall(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
+    mut target_resources: ResMut<TargetResources>,
 ) {
-    commands.spawn((
+    // spawn the wall
+    //
+    let mut wall_commands = commands.spawn((
+        TargetWall,
         Mesh3d(meshes.add(Cuboid::from_corners(
             Vec3::ZERO, WALL_SIZE
         ))),
@@ -56,7 +113,7 @@ fn setup_target_wall(
             base_color: WALL_COLOR,
             ..default()
         })),
-        Transform::from_xyz(0.0, WALL_SIZE.y * 0.5, WALL_FACE_Z - WALL_SIZE.z * 0.5),
+        Transform::from_xyz(0.0, WALL_SIZE.y * 0.5, WALL_FACE_Z),
         Collider::cuboid(WALL_SIZE.x, WALL_SIZE.y, WALL_SIZE.z * 0.5),
         RigidBody::Static,
     ));
@@ -73,35 +130,49 @@ fn setup_target_wall(
         TARGET_RADIUS, TARGET_HEIGHT
     );
 
-    let targets: Box<[_;TARGET_COUNT]> = Box::new(std::array::from_fn(|_| (
+    // spawn the targets as children of the wall
+    //
+    (0..TARGET_COUNT).for_each(|_|
+    {
+        let handle = target_resources.new_handle();
+        let transform = target_resources.random_transform(&handle);
+
+        wall_commands.with_child((
             Target,
+            handle,
             Mesh3d(target_mesh.clone()),
             MeshMaterial3d(target_material.clone()),
-        Target::random_transform(),
+            transform,
             target_collider.clone(),
             RigidBody::Static,
-    )));
-    commands.spawn_batch(targets.into_iter());
+        ));
+    });
 }
 
 fn on_targets_shot(
     mut collision_events: EventReader<CollisionEnded>,
-    mut bullet_query: Query<Entity, With<Bullet>>,
-    mut target_query: Query<&mut Transform, With<Target>>,
+    mut query_set: ParamSet<(
+        Query<Entity, With<Bullet>>,
+        Query<(&TargetHandle, &mut Transform), With<Target>>,
+    )>,
+    mut target_resources: ResMut<TargetResources>,
 ) {
     for collision in collision_events.read()
     {
         // resolve the query data from the collision, if the collision is
         // between a bullet and a target
         //
-        let Ok(_) = collision.query_unique(&mut bullet_query) else {
-            continue;
+        let bullet_query = &mut query_set.p0();
+        let Ok(_) = collision.query_unique(bullet_query) else {
+            continue; // the collision doesn't involve a bullet
         };
-        let Ok(mut target_transform) = collision.query_unique(&mut target_query) else {
-            continue;
+        //
+        let target_query = &mut query_set.p1();
+        let Ok((target_handle, mut target_transform)) = collision.query_unique(target_query) else {
+            continue; // the collision doesn't involve a target
         };
 
         // move the target
-        *target_transform = Target::random_transform();
+        *target_transform = target_resources.random_transform(target_handle);
     }
 }