single global observers root node (#25)

plus auto name observer macro `global_observer`

src/abilities/gun.rs

@@ -1,7 +1,7 @@
 use super::{Projectile, TriggerGun};
 use crate::{
-    GameState, billboards::Billboard, loading_assets::GameAssets, physics_layers::GameLayer,
-    sounds::PlaySound, utils::sprite_3d_animation::AnimationTimer,
+    GameState, billboards::Billboard, global_observer, loading_assets::GameAssets,
+    physics_layers::GameLayer, sounds::PlaySound, utils::sprite_3d_animation::AnimationTimer,
 };
 use avian3d::prelude::{
     Collider, CollisionLayers, CollisionStarted, LayerMask, PhysicsLayer, Sensor,
@@ -30,7 +30,8 @@ pub fn plugin(app: &mut App) {
         Update,
         (update, shot_collision, timeout).run_if(in_state(GameState::Playing)),
     );
-    app.add_observer(on_trigger_state);
+
+    global_observer!(app, on_trigger_gun);
 }
 
 fn setup(mut commands: Commands, assets: Res<GameAssets>, mut sprite_params: Sprite3dParams) {
@@ -43,7 +44,7 @@ fn setup(mut commands: Commands, assets: Res<GameAssets>, mut sprite_params: Spr
     });
 }
 
-fn on_trigger_state(
+fn on_trigger_gun(
     trigger: Trigger<TriggerGun>,
     mut commands: Commands,
     query_transform: Query<&Transform>,

src/abilities/mod.rs

@@ -4,6 +4,7 @@ mod thrown;
 use crate::{
     GameState,
     aim::AimTarget,
+    global_observer,
     heads::ActiveHeads,
     hitpoints::Hit,
     physics_layers::GameLayer,
@@ -74,7 +75,7 @@ pub fn plugin(app: &mut App) {
 
     app.add_systems(Update, enemy_hit.run_if(in_state(GameState::Playing)));
 
-    app.add_observer(on_trigger_state);
+    global_observer!(app, on_trigger_state);
 }
 
 fn enemy_hit(

src/abilities/thrown.rs

@@ -1,7 +1,12 @@
 use super::TriggerThrow;
 use crate::{
-    GameState, billboards::Billboard, hitpoints::Hit, loading_assets::GameAssets,
-    physics_layers::GameLayer, sounds::PlaySound, utils::sprite_3d_animation::AnimationTimer,
+    GameState,
+    billboards::Billboard,
+    hitpoints::Hit,
+    loading_assets::GameAssets,
+    physics_layers::GameLayer,
+    sounds::PlaySound,
+    utils::{global_observer, sprite_3d_animation::AnimationTimer},
 };
 use avian3d::prelude::*;
 use bevy::{pbr::NotShadowCaster, prelude::*};
@@ -35,8 +40,9 @@ pub fn plugin(app: &mut App) {
     app.add_systems(OnEnter(GameState::Playing), setup);
     app.add_systems(Update, shot_collision.run_if(in_state(GameState::Playing)));
     app.add_systems(FixedUpdate, update_auto_rotation);
-    app.add_observer(on_trigger_state);
-    app.add_observer(on_explosion);
+
+    global_observer!(app, on_trigger_thrown);
+    global_observer!(app, on_explosion);
 }
 
 fn on_explosion(
@@ -75,7 +81,7 @@ fn setup(mut commands: Commands, assets: Res<GameAssets>, mut sprite_params: Spr
     });
 }
 
-fn on_trigger_state(
+fn on_trigger_thrown(
     trigger: Trigger<TriggerThrow>,
     mut commands: Commands,
     query_transform: Query<&Transform>,