From 01e6e944d3631323c9755dea57b99cfe2c1cb477 Mon Sep 17 00:00:00 2001
From: extrawurst <mail@rusticorn.com>
Date: Wed, 2 Apr 2025 01:35:02 +0800
Subject: [PATCH] ammo system

* heads have abilities
* health and ammo shows in ui
---
 src/abilities/gun.rs          | 103 +++++++++++--------------
 src/abilities/mod.rs          |  71 ++++++++++++++++-
 src/abilities/thrown.rs       | 103 +++++++++++--------------
 src/active_heads.rs           | 138 ++++++++++++++++++++++++++++++++++
 src/aim/target_ui.rs          |   6 +-
 src/backpack/backpack_ui.rs   |   6 +-
 src/backpack/mod.rs           |  40 ++--------
 src/backpack/ui_head_state.rs |  30 ++++++++
 src/control/controls.rs       |   2 +-
 src/heads_ui.rs               |  89 +++++-----------------
 src/main.rs                   |   2 +
 src/npc.rs                    |   2 +-
 src/player.rs                 |   2 +-
 13 files changed, 360 insertions(+), 234 deletions(-)
 create mode 100644 src/active_heads.rs
 create mode 100644 src/backpack/ui_head_state.rs

diff --git a/src/abilities/gun.rs b/src/abilities/gun.rs
index 50ff525..f01598e 100644
--- a/src/abilities/gun.rs
+++ b/src/abilities/gun.rs
@@ -1,4 +1,4 @@
-use super::{Projectile, TriggerState};
+use super::{Projectile, TriggerGun};
 use crate::{
     GameState,
     aim::AimState,
@@ -50,77 +50,60 @@ fn setup(mut commands: Commands, assets: Res<GameAssets>, mut sprite_params: Spr
 }
 
 fn on_trigger_state(
-    trigger: Trigger<TriggerState>,
+    trigger: Trigger<TriggerGun>,
     mut commands: Commands,
     aim: Res<AimState>,
-    player_rot: Query<&Transform, With<PlayerRig>>,
-    player: Query<(&Transform, &Player)>,
     target_transform: Query<&Transform, (Without<Player>, Without<PlayerRig>)>,
     time: Res<Time>,
     mut polyline_materials: ResMut<Assets<PolylineMaterial>>,
     mut polylines: ResMut<Assets<Polyline>>,
 ) {
-    if matches!(trigger.event(), TriggerState::Active) {
-        let Some((player_pos, player_head)) =
-            player.iter().next().map(|(t, p)| (t.translation, p.0))
-        else {
-            return;
-        };
+    let state = trigger.0;
 
-        // TODO: proper weapon classes
-        if ![2, 3, 9].contains(&player_head) {
-            return;
-        }
+    commands.trigger(PlaySound::Gun);
 
-        commands.trigger(PlaySound::Gun);
+    let rotation = if let Some(target) = aim.target {
+        let t = target_transform
+            .get(target)
+            .expect("target must have transform");
+        Transform::from_translation(state.pos)
+            .looking_at(t.translation, Vec3::Y)
+            .rotation
+    } else {
+        state.rot.mul_quat(Quat::from_rotation_y(PI))
+    };
 
-        let Some(rotation) = player_rot.iter().next().map(|t| t.rotation) else {
-            return;
-        };
+    let mut t = Transform::from_translation(state.pos).with_rotation(rotation);
+    t.translation += t.forward().as_vec3() * 2.;
 
-        let rotation = if let Some(target) = aim.target {
-            let t = target_transform
-                .get(target)
-                .expect("target must have transform");
-            Transform::from_translation(player_pos)
-                .looking_at(t.translation, Vec3::Y)
-                .rotation
-        } else {
-            rotation.mul_quat(Quat::from_rotation_y(PI))
-        };
-
-        let mut t = Transform::from_translation(player_pos).with_rotation(rotation);
-        t.translation += t.forward().as_vec3() * 2.;
-
-        commands
-            .spawn((
-                Name::new("projectile-gun"),
-                GunProjectile {
-                    time: time.elapsed_secs(),
-                },
-                Projectile { damage: 10 },
-                Collider::capsule_endpoints(0.5, Vec3::new(0., 0., 0.), Vec3::new(0., 0., -3.)),
-                CollisionLayers::new(
-                    LayerMask(GameLayer::Projectile.to_bits()),
-                    LayerMask(GameLayer::Npc.to_bits() | GameLayer::Level.to_bits()),
-                ),
-                Sensor,
-                Visibility::default(),
-                t,
-            ))
-            .with_child(PolylineBundle {
-                polyline: PolylineHandle(polylines.add(Polyline {
-                    vertices: vec![Vec3::Z * 2., Vec3::Z * -2.],
-                })),
-                material: PolylineMaterialHandle(polyline_materials.add(PolylineMaterial {
-                    width: 10.0,
-                    color: LinearRgba::rgb(0.9, 0.9, 0.),
-                    perspective: false,
-                    ..default()
-                })),
+    commands
+        .spawn((
+            Name::new("projectile-gun"),
+            GunProjectile {
+                time: time.elapsed_secs(),
+            },
+            Projectile { damage: 10 },
+            Collider::capsule_endpoints(0.5, Vec3::new(0., 0., 0.), Vec3::new(0., 0., -3.)),
+            CollisionLayers::new(
+                LayerMask(GameLayer::Projectile.to_bits()),
+                LayerMask(GameLayer::Npc.to_bits() | GameLayer::Level.to_bits()),
+            ),
+            Sensor,
+            Visibility::default(),
+            t,
+        ))
+        .with_child(PolylineBundle {
+            polyline: PolylineHandle(polylines.add(Polyline {
+                vertices: vec![Vec3::Z * 2., Vec3::Z * -2.],
+            })),
+            material: PolylineMaterialHandle(polyline_materials.add(PolylineMaterial {
+                width: 10.0,
+                color: LinearRgba::rgb(0.9, 0.9, 0.),
+                perspective: false,
                 ..default()
-            });
-    }
+            })),
+            ..default()
+        });
 }
 
 fn update(mut query: Query<&mut Transform, With<GunProjectile>>) {
diff --git a/src/abilities/mod.rs b/src/abilities/mod.rs
index 171a4ae..d0b02dc 100644
--- a/src/abilities/mod.rs
+++ b/src/abilities/mod.rs
@@ -1,7 +1,13 @@
 mod gun;
 mod thrown;
 
-use crate::{GameState, npc::Hit, tb_entities::EnemySpawn};
+use crate::{
+    GameState,
+    active_heads::ActiveHeads,
+    npc::Hit,
+    player::{Player, PlayerRig},
+    tb_entities::EnemySpawn,
+};
 use avian3d::prelude::*;
 use bevy::prelude::*;
 
@@ -16,11 +22,33 @@ pub enum TriggerState {
     Inactive,
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Reflect)]
+pub enum HeadAbility {
+    None,
+    Arrow,
+    Thrown,
+    Gun,
+}
+
+#[derive(Debug, Reflect, Clone, Copy)]
+pub struct PlayerTriggerState {
+    dir: Dir3,
+    rot: Quat,
+    pos: Vec3,
+}
+
+#[derive(Event, Reflect)]
+pub struct TriggerGun(pub PlayerTriggerState);
+#[derive(Event, Reflect)]
+pub struct TriggerThrow(pub PlayerTriggerState);
+
 pub fn plugin(app: &mut App) {
     app.add_plugins(gun::plugin);
     app.add_plugins(thrown::plugin);
 
     app.add_systems(Update, enemy_hit.run_if(in_state(GameState::Playing)));
+
+    app.add_observer(on_trigger_state);
 }
 
 fn enemy_hit(
@@ -47,3 +75,44 @@ fn enemy_hit(
         commands.entity(enemy_entity).trigger(Hit { damage });
     }
 }
+
+fn on_trigger_state(
+    trigger: Trigger<TriggerState>,
+    mut commands: Commands,
+    player_rot: Query<&Transform, With<PlayerRig>>,
+    player_transform: Query<&Transform, With<Player>>,
+    mut active_heads: ResMut<ActiveHeads>,
+) {
+    if matches!(trigger.event(), TriggerState::Active) {
+        let Some(state) = active_heads.current() else {
+            return;
+        };
+
+        if !state.has_ammo() {
+            //TOOD: play sound
+            return;
+        }
+
+        let Some(transform) = player_transform.iter().next().copied() else {
+            return;
+        };
+
+        let Some((rot, dir)) = player_rot.iter().next().map(|t| (t.rotation, t.forward())) else {
+            return;
+        };
+
+        let trigger_state = PlayerTriggerState {
+            dir,
+            rot,
+            pos: transform.translation,
+        };
+
+        active_heads.use_ammo();
+
+        match state.ability {
+            HeadAbility::Thrown => commands.trigger(TriggerThrow(trigger_state)),
+            HeadAbility::Gun => commands.trigger(TriggerGun(trigger_state)),
+            _ => (),
+        };
+    }
+}
diff --git a/src/abilities/thrown.rs b/src/abilities/thrown.rs
index d985589..7961aaa 100644
--- a/src/abilities/thrown.rs
+++ b/src/abilities/thrown.rs
@@ -1,4 +1,4 @@
-use super::TriggerState;
+use super::TriggerThrow;
 use crate::{
     GameState,
     aim::AimState,
@@ -83,77 +83,58 @@ fn setup(mut commands: Commands, assets: Res<GameAssets>, mut sprite_params: Spr
 }
 
 fn on_trigger_state(
-    trigger: Trigger<TriggerState>,
+    trigger: Trigger<TriggerThrow>,
     mut commands: Commands,
     aim: Res<AimState>,
-    player_rot: Query<&Transform, With<PlayerRig>>,
-    player: Query<(&Transform, &Player)>,
     target_transform: Query<&Transform, (Without<Player>, Without<PlayerRig>)>,
     assets: Res<GameAssets>,
 ) {
-    if matches!(trigger.event(), TriggerState::Active) {
-        let Some((player_pos, player_head)) =
-            player.iter().next().map(|(t, p)| (t.translation, p.0))
-        else {
-            return;
-        };
+    let state = trigger.event().0;
 
-        // TODO: proper weapon classes
-        if ![0, 8, 16, 17].contains(&player_head) {
-            return;
-        }
+    commands.trigger(PlaySound::Throw);
 
-        commands.trigger(PlaySound::Throw);
+    const SPEED: f32 = 35.;
 
-        let Some((rotation, player_forward)) =
-            player_rot.iter().next().map(|t| (t.rotation, t.forward()))
-        else {
-            return;
-        };
+    let vel = if let Some(target) = aim.target {
+        let t = target_transform
+            .get(target)
+            .expect("target must have transform");
 
-        const SPEED: f32 = 35.;
+        launch_velocity(
+            state.pos + state.dir.as_vec3() * 2.,
+            t.translation,
+            SPEED,
+            9.81,
+        )
+        .map(|(low, _)| low)
+        .unwrap()
+    } else {
+        state.rot.mul_quat(Quat::from_rotation_y(-PI / 2.))
+            * (Vec3::new(2., 1., 0.).normalize() * SPEED)
+    };
 
-        let vel = if let Some(target) = aim.target {
-            let t = target_transform
-                .get(target)
-                .expect("target must have transform");
+    let t = Transform::from_translation(state.pos);
 
-            launch_velocity(
-                player_pos + player_forward.as_vec3() * 2.,
-                t.translation,
-                SPEED,
-                9.81,
-            )
-            .map(|(low, _)| low)
-            .unwrap()
-        } else {
-            rotation.mul_quat(Quat::from_rotation_y(-PI / 2.))
-                * (Vec3::new(2., 1., 0.).normalize() * SPEED)
-        };
-
-        let t = Transform::from_translation(player_pos);
-
-        commands
-            .spawn((
-                Name::new("projectile-thrown"),
-                ThrownProjectile,
-                Collider::sphere(0.5),
-                CollisionLayers::new(
-                    LayerMask(GameLayer::Projectile.to_bits()),
-                    LayerMask(GameLayer::Npc.to_bits() | GameLayer::Level.to_bits()),
-                ),
-                RigidBody::Dynamic,
-                Mass(0.01),
-                LinearVelocity(vel),
-                Visibility::default(),
-                t,
-            ))
-            .with_child((
-                AutoRotation(Quat::from_rotation_x(0.4) * Quat::from_rotation_z(0.3)),
-                Transform::from_scale(Vec3::splat(10.)),
-                SceneRoot(assets.molotov.clone()),
-            ));
-    }
+    commands
+        .spawn((
+            Name::new("projectile-thrown"),
+            ThrownProjectile,
+            Collider::sphere(0.5),
+            CollisionLayers::new(
+                LayerMask(GameLayer::Projectile.to_bits()),
+                LayerMask(GameLayer::Npc.to_bits() | GameLayer::Level.to_bits()),
+            ),
+            RigidBody::Dynamic,
+            Mass(0.01),
+            LinearVelocity(vel),
+            Visibility::default(),
+            t,
+        ))
+        .with_child((
+            AutoRotation(Quat::from_rotation_x(0.4) * Quat::from_rotation_z(0.3)),
+            Transform::from_scale(Vec3::splat(10.)),
+            SceneRoot(assets.molotov.clone()),
+        ));
 }
 
 fn shot_collision(
diff --git a/src/active_heads.rs b/src/active_heads.rs
new file mode 100644
index 0000000..5e84675
--- /dev/null
+++ b/src/active_heads.rs
@@ -0,0 +1,138 @@
+use crate::{
+    abilities::HeadAbility,
+    backpack::{BackbackSwapEvent, Backpack},
+    sounds::PlaySound,
+};
+use bevy::prelude::*;
+
+pub static HEAD_COUNT: usize = 18;
+pub static HEAD_SLOTS: usize = 5;
+
+#[derive(Clone, Copy, Debug, PartialEq, Reflect)]
+pub struct HeadState {
+    pub head: usize,
+    pub ability: HeadAbility,
+    pub health: u32,
+    pub health_max: u32,
+    pub ammo: u32,
+    pub ammo_max: u32,
+}
+
+impl HeadState {
+    pub fn new(head: usize, ammo: u32) -> Self {
+        Self {
+            head,
+            health: 100,
+            health_max: 100,
+            ammo,
+            ammo_max: ammo,
+            ability: HeadAbility::None,
+        }
+    }
+
+    fn with_ability(mut self, ability: HeadAbility) -> Self {
+        self.ability = ability;
+        self
+    }
+
+    pub fn has_ammo(&self) -> bool {
+        self.ammo > 0
+    }
+}
+
+#[derive(Resource, Default, Reflect)]
+#[reflect(Resource)]
+pub struct ActiveHeads {
+    heads: [Option<HeadState>; 5],
+    current_slot: usize,
+}
+
+impl ActiveHeads {
+    pub fn current(&self) -> Option<HeadState> {
+        self.heads[self.current_slot]
+    }
+
+    pub fn use_ammo(&mut self) {
+        let Some(head) = &mut self.heads[self.current_slot] else {
+            error!("cannot use ammo of empty head");
+            return;
+        };
+
+        head.ammo = head.ammo.saturating_sub(1);
+    }
+
+    pub fn slot(&self) -> usize {
+        self.current_slot
+    }
+
+    pub fn head(&self, slot: usize) -> Option<HeadState> {
+        self.heads[slot]
+    }
+}
+
+#[derive(Event, Reflect)]
+pub enum SelectActiveHead {
+    Left,
+    Right,
+}
+
+#[derive(Event)]
+pub struct HeadChanged(pub usize);
+
+pub fn plugin(app: &mut App) {
+    app.insert_resource(ActiveHeads {
+        heads: [
+            Some(HeadState::new(0, 10).with_ability(HeadAbility::Thrown)),
+            Some(HeadState::new(3, 10).with_ability(HeadAbility::Gun)),
+            Some(HeadState::new(6, 10).with_ability(HeadAbility::Arrow)),
+            Some(HeadState::new(8, 10).with_ability(HeadAbility::Thrown)),
+            Some(HeadState::new(9, 10).with_ability(HeadAbility::Gun)),
+        ],
+        current_slot: 0,
+    });
+
+    app.add_observer(on_select_active_head);
+    app.add_observer(on_swap_backpack);
+}
+
+fn on_select_active_head(
+    trigger: Trigger<SelectActiveHead>,
+    mut commands: Commands,
+    mut res: ResMut<ActiveHeads>,
+) {
+    match trigger.event() {
+        SelectActiveHead::Right => {
+            res.current_slot = (res.current_slot + 1) % HEAD_SLOTS;
+        }
+        SelectActiveHead::Left => {
+            res.current_slot = (res.current_slot + (HEAD_SLOTS - 1)) % HEAD_SLOTS;
+        }
+    }
+
+    commands.trigger(PlaySound::Selection);
+    commands.trigger(HeadChanged(res.heads[res.current_slot].unwrap().head));
+}
+
+fn on_swap_backpack(
+    trigger: Trigger<BackbackSwapEvent>,
+    mut commands: Commands,
+    mut res: ResMut<ActiveHeads>,
+    mut backpack: ResMut<Backpack>,
+) {
+    let backpack_slot = trigger.event().0;
+
+    let head = backpack.heads.get(backpack_slot).unwrap();
+
+    let current_active_slot = res.current_slot;
+
+    let current_active_head = res.heads[current_active_slot];
+    res.heads[current_active_slot] = Some(*head);
+
+    if let Some(old_active) = current_active_head {
+        backpack.heads[backpack_slot] = old_active;
+    } else {
+        backpack.heads.remove(backpack_slot);
+    }
+
+    commands.trigger(HeadChanged(res.heads[res.current_slot].unwrap().head));
+}
diff --git a/src/aim/target_ui.rs b/src/aim/target_ui.rs
index e90ba78..e0dee53 100644
--- a/src/aim/target_ui.rs
+++ b/src/aim/target_ui.rs
@@ -1,7 +1,7 @@
 use super::AimState;
 use crate::{
     GameState,
-    backpack::BackpackHead,
+    backpack::UiHeadState,
     heads_ui::HeadsImages,
     loading_assets::UIAssets,
     npc::{Hitpoints, NpcHead},
@@ -18,7 +18,7 @@ struct HeadDamage;
 
 #[derive(Resource, Default, PartialEq)]
 struct TargetUi {
-    head: Option<BackpackHead>,
+    head: Option<UiHeadState>,
 }
 
 pub fn plugin(app: &mut App) {
@@ -150,7 +150,7 @@ fn sync(
     let mut new_state = None;
     if let Some(e) = aim.target {
         if let Ok((hp, head)) = target_data.get(e) {
-            new_state = Some(BackpackHead {
+            new_state = Some(UiHeadState {
                 head: head.0,
                 health: hp.health(),
                 ammo: 1.,
diff --git a/src/backpack/backpack_ui.rs b/src/backpack/backpack_ui.rs
index 6eacd78..b66f77b 100644
--- a/src/backpack/backpack_ui.rs
+++ b/src/backpack/backpack_ui.rs
@@ -1,4 +1,4 @@
-use super::{BackbackSwapEvent, Backpack, BackpackHead};
+use super::{BackbackSwapEvent, Backpack, UiHeadState};
 use crate::{GameState, heads_ui::HeadsImages, loading_assets::UIAssets, sounds::PlaySound};
 use bevy::prelude::*;
 
@@ -29,7 +29,7 @@ struct HeadDamage(pub usize);
 
 #[derive(Resource, Default, Debug)]
 struct BackpackUiState {
-    heads: [Option<BackpackHead>; 5],
+    heads: [Option<UiHeadState>; 5],
     scroll: usize,
     count: usize,
     current_slot: usize,
@@ -316,7 +316,7 @@ fn sync(backpack: &Res<Backpack>, state: &mut ResMut<BackpackUiState>) {
 
     for i in 0..HEAD_SLOTS {
         if let Some(head) = backpack.heads.get(i + state.scroll) {
-            state.heads[i] = Some(*head);
+            state.heads[i] = Some(UiHeadState::from(*head));
         } else {
             state.heads[i] = None;
         }
diff --git a/src/backpack/mod.rs b/src/backpack/mod.rs
index bdfd3dc..a418acb 100644
--- a/src/backpack/mod.rs
+++ b/src/backpack/mod.rs
@@ -1,38 +1,18 @@
 mod backpack_ui;
+mod ui_head_state;
 
-use crate::{GameState, heads_ui::HEAD_COUNT};
+use crate::{
+    GameState,
+    active_heads::{HEAD_COUNT, HeadState},
+};
 use bevy::prelude::*;
 
 pub use backpack_ui::BackpackAction;
-
-#[derive(Clone, Copy, Debug, PartialEq, Reflect)]
-pub struct BackpackHead {
-    pub head: usize,
-    pub health: f32,
-    pub ammo: f32,
-}
-
-impl BackpackHead {
-    pub fn new(head: usize) -> Self {
-        Self {
-            head,
-            health: 1.0,
-            ammo: 1.0,
-        }
-    }
-
-    pub fn damage(&self) -> f32 {
-        1. - self.health
-    }
-
-    pub fn ammo_used(&self) -> f32 {
-        1. - self.ammo
-    }
-}
+pub use ui_head_state::UiHeadState;
 
 #[derive(Resource, Default)]
 pub struct Backpack {
-    pub heads: Vec<BackpackHead>,
+    pub heads: Vec<HeadState>,
 }
 
 #[derive(Event)]
@@ -47,11 +27,7 @@ pub fn plugin(app: &mut App) {
 fn setup(mut commands: Commands) {
     commands.insert_resource(Backpack {
         heads: (0usize..HEAD_COUNT)
-            .map(|i| BackpackHead {
-                head: i,
-                health: 1.,
-                ammo: 1.,
-            })
+            .map(|i| HeadState::new(i, 10))
             .collect(),
     });
 }
diff --git a/src/backpack/ui_head_state.rs b/src/backpack/ui_head_state.rs
new file mode 100644
index 0000000..55bbcd6
--- /dev/null
+++ b/src/backpack/ui_head_state.rs
@@ -0,0 +1,30 @@
+use bevy::prelude::*;
+
+use crate::active_heads::HeadState;
+
+#[derive(Clone, Copy, Debug, PartialEq, Reflect, Default)]
+pub struct UiHeadState {
+    pub head: usize,
+    pub health: f32,
+    pub ammo: f32,
+}
+
+impl UiHeadState {
+    pub fn damage(&self) -> f32 {
+        1. - self.health
+    }
+
+    pub fn ammo_used(&self) -> f32 {
+        1. - self.ammo
+    }
+}
+
+impl From<HeadState> for UiHeadState {
+    fn from(value: HeadState) -> Self {
+        Self {
+            head: value.head,
+            ammo: value.ammo as f32 / value.ammo_max as f32,
+            health: value.health as f32 / value.health_max as f32,
+        }
+    }
+}
diff --git a/src/control/controls.rs b/src/control/controls.rs
index 32908e2..9b45176 100644
--- a/src/control/controls.rs
+++ b/src/control/controls.rs
@@ -1,5 +1,5 @@
 use crate::{
-    GameState, abilities::TriggerState, backpack::BackpackAction, heads_ui::SelectActiveHead,
+    GameState, abilities::TriggerState, active_heads::SelectActiveHead, backpack::BackpackAction,
 };
 use bevy::{
     input::{
diff --git a/src/heads_ui.rs b/src/heads_ui.rs
index 2385dd8..997880a 100644
--- a/src/heads_ui.rs
+++ b/src/heads_ui.rs
@@ -1,23 +1,14 @@
 use crate::{
     GameState,
-    backpack::{BackbackSwapEvent, Backpack, BackpackHead},
+    active_heads::{ActiveHeads, HEAD_COUNT, HEAD_SLOTS},
+    backpack::UiHeadState,
     loading_assets::UIAssets,
     player::head_id_to_str,
-    sounds::PlaySound,
 };
 use bevy::prelude::*;
 use bevy_ui_gradients::{AngularColorStop, BackgroundGradient, ConicGradient, Gradient, Position};
 use std::f32::consts::PI;
 
-pub static HEAD_COUNT: usize = 18;
-static HEAD_SLOTS: usize = 5;
-
-#[derive(Event, Reflect)]
-pub enum SelectActiveHead {
-    Left,
-    Right,
-}
-
 #[derive(Component, Reflect, Default)]
 #[reflect(Component)]
 struct HeadSelector(pub usize);
@@ -37,25 +28,20 @@ pub struct HeadsImages {
 
 #[derive(Resource, Default, Reflect)]
 #[reflect(Resource)]
-pub struct ActiveHeads {
-    heads: [Option<BackpackHead>; 5],
+struct UiActiveHeads {
+    heads: [Option<UiHeadState>; 5],
     current_slot: usize,
 }
 
-#[derive(Event)]
-pub struct HeadChanged(pub usize);
-
 pub fn plugin(app: &mut App) {
     app.register_type::<HeadDamage>();
-    app.register_type::<ActiveHeads>();
+    app.register_type::<UiActiveHeads>();
 
     app.add_systems(OnEnter(GameState::Playing), setup);
     app.add_systems(
         Update,
-        (update, update_ammo, update_health).run_if(in_state(GameState::Playing)),
+        (sync, update, update_ammo, update_health).run_if(in_state(GameState::Playing)),
     );
-    app.add_observer(on_select_active_head);
-    app.add_observer(on_swap_backpack);
 }
 
 fn setup(mut commands: Commands, asset_server: Res<AssetServer>, assets: Res<UIAssets>) {
@@ -87,16 +73,7 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>, assets: Res<UIA
 
     commands.insert_resource(HeadsImages { heads });
 
-    commands.insert_resource(ActiveHeads {
-        heads: [
-            Some(BackpackHead::new(0)),
-            Some(BackpackHead::new(3)),
-            Some(BackpackHead::new(6)),
-            Some(BackpackHead::new(8)),
-            Some(BackpackHead::new(9)),
-        ],
-        current_slot: 0,
-    });
+    commands.init_resource::<UiActiveHeads>();
 }
 
 fn spawn_head_ui(
@@ -190,7 +167,7 @@ fn spawn_head_ui(
 }
 
 fn update(
-    res: Res<ActiveHeads>,
+    res: Res<UiActiveHeads>,
     heads_images: Res<HeadsImages>,
     mut head_image: Query<(&HeadImage, &mut Visibility, &mut ImageNode), Without<HeadSelector>>,
     mut head_selector: Query<(&HeadSelector, &mut Visibility), Without<HeadImage>>,
@@ -214,7 +191,10 @@ fn update(
     }
 }
 
-fn update_ammo(res: Res<ActiveHeads>, mut gradients: Query<(&mut BackgroundGradient, &HeadImage)>) {
+fn update_ammo(
+    res: Res<UiActiveHeads>,
+    mut gradients: Query<(&mut BackgroundGradient, &HeadImage)>,
+) {
     if res.is_changed() {
         for (mut gradient, HeadImage(head)) in gradients.iter_mut() {
             if let Some(head) = res.heads[*head] {
@@ -230,7 +210,7 @@ fn update_ammo(res: Res<ActiveHeads>, mut gradients: Query<(&mut BackgroundGradi
     }
 }
 
-fn update_health(res: Res<ActiveHeads>, mut query: Query<(&mut Node, &HeadDamage)>) {
+fn update_health(res: Res<UiActiveHeads>, mut query: Query<(&mut Node, &HeadDamage)>) {
     if res.is_changed() {
         for (mut node, HeadDamage(head)) in query.iter_mut() {
             node.height =
@@ -239,44 +219,11 @@ fn update_health(res: Res<ActiveHeads>, mut query: Query<(&mut Node, &HeadDamage
     }
 }
 
-fn on_select_active_head(
-    trigger: Trigger<SelectActiveHead>,
-    mut commands: Commands,
-    mut res: ResMut<ActiveHeads>,
-) {
-    match trigger.event() {
-        SelectActiveHead::Right => {
-            res.current_slot = (res.current_slot + 1) % HEAD_SLOTS;
-        }
-        SelectActiveHead::Left => {
-            res.current_slot = (res.current_slot + (HEAD_SLOTS - 1)) % HEAD_SLOTS;
+fn sync(active: Res<ActiveHeads>, mut state: ResMut<UiActiveHeads>) {
+    if active.is_changed() {
+        state.current_slot = active.slot();
+        for i in 0..HEAD_SLOTS {
+            state.heads[i] = active.head(i).map(UiHeadState::from);
         }
     }
-
-    commands.trigger(PlaySound::Selection);
-    commands.trigger(HeadChanged(res.heads[res.current_slot].unwrap().head));
-}
-
-fn on_swap_backpack(
-    trigger: Trigger<BackbackSwapEvent>,
-    mut commands: Commands,
-    mut res: ResMut<ActiveHeads>,
-    mut backpack: ResMut<Backpack>,
-) {
-    let backpack_slot = trigger.event().0;
-
-    let head = backpack.heads.get(backpack_slot).unwrap();
-
-    let current_active_slot = res.current_slot;
-
-    let current_active_head = res.heads[current_active_slot];
-    res.heads[current_active_slot] = Some(*head);
-
-    if let Some(old_active) = current_active_head {
-        backpack.heads[backpack_slot] = old_active;
-    } else {
-        backpack.heads.remove(backpack_slot);
-    }
-
-    commands.trigger(HeadChanged(res.heads[res.current_slot].unwrap().head));
 }
diff --git a/src/main.rs b/src/main.rs
index 8ebbbe5..cfd26e8 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,5 @@
 mod abilities;
+mod active_heads;
 mod aim;
 mod alien;
 mod backpack;
@@ -116,6 +117,7 @@ fn main() {
     app.add_plugins(loading_map::plugin);
     app.add_plugins(sprite_3d_animation::plugin);
     app.add_plugins(abilities::plugin);
+    app.add_plugins(active_heads::plugin);
 
     app.init_state::<GameState>();
 
diff --git a/src/npc.rs b/src/npc.rs
index 90d4d70..1315e44 100644
--- a/src/npc.rs
+++ b/src/npc.rs
@@ -1,5 +1,5 @@
 use crate::{
-    GameState, heads_ui::HEAD_COUNT, keys::KeySpawn, player::head_id_to_str, sounds::PlaySound,
+    GameState, active_heads::HEAD_COUNT, keys::KeySpawn, player::head_id_to_str, sounds::PlaySound,
     tb_entities::EnemySpawn,
 };
 use bevy::prelude::*;
diff --git a/src/player.rs b/src/player.rs
index d9f7e06..78781e0 100644
--- a/src/player.rs
+++ b/src/player.rs
@@ -1,5 +1,6 @@
 use crate::{
     GameState,
+    active_heads::HeadChanged,
     alien::Animations,
     camera::{CameraArmRotation, CameraTarget},
     cash::{Cash, CashCollectEvent},
@@ -7,7 +8,6 @@ use crate::{
         Controls,
         controller::{CharacterControllerBundle, MovementBundle, PlayerMovement},
     },
-    heads_ui::HeadChanged,
     loading_assets::GameAssets,
     physics_layers::GameLayer,
     sounds::PlaySound,