feat: hitscan projectiles

src/game/level.rs

@@ -1,60 +0,0 @@
-
-use bevy::prelude::*;
-use avian3d::prelude::*;
-
-use super::target_wall::TargetWallPlugin;
-
-pub struct LevelPlugin;
-
-impl Plugin for LevelPlugin
-{
-    fn build(&self, app: &mut App)
-    {
-        app.add_plugins(TargetWallPlugin);
-        app.add_systems(Startup, setup_level);
-    }
-}
-
-fn setup_level(
-    mut commands: Commands,
-    mut meshes: ResMut<Assets<Mesh>>,
-    mut materials: ResMut<Assets<StandardMaterial>>,
-) {
-    const GROUND_SIZE: f32 = 100.0;
-
-    // spawn the ground plane
-    commands.spawn((
-        Mesh3d(meshes.add(Plane3d::new(Vec3::Y, Vec2::splat(GROUND_SIZE * 0.5)))),
-        MeshMaterial3d(materials.add(StandardMaterial {
-            base_color: Color::srgb(0.761, 0.698, 0.502),
-            ..default()
-        })),
-        Transform::IDENTITY,
-        Collider::cuboid(GROUND_SIZE, 0.0, GROUND_SIZE),
-        RigidBody::Static,
-    ));
-
-    // spawn a box
-    commands.spawn((
-        Mesh3d(meshes.add(Cuboid::from_corners(
-            Vec3::new(-0.5, -0.5, -0.5), Vec3::new(0.5, 0.5, 0.5)
-        ))),
-        MeshMaterial3d(materials.add(StandardMaterial {
-            base_color: Color::srgb(0.7, 0.1, 0.1),
-            ..default()
-        })),
-        Transform::from_xyz(2.0, 0.5, -5.0),
-        Collider::cuboid(1.0, 1.0, 1.0),
-        RigidBody::Dynamic,
-    ));
-
-    // spawn a light source
-    commands.spawn((
-        DirectionalLight {
-            illuminance: light_consts::lux::AMBIENT_DAYLIGHT,
-            shadows_enabled: true,
-            ..default()
-        },
-        Transform::from_xyz(100.0, 200.0, 100.0).looking_at(Vec3::ZERO, Vec3::Y),
-    ));
-}

src/game/mod.rs

@@ -1,8 +1,15 @@
 
+use bevy::input::ButtonState;
 use bevy::prelude::*;
+use bevy::input::mouse::MouseButtonInput;
+use avian3d::prelude::*;
+
+use crate::physics::{ProjectileData, ProjectileSpawner};
+use crate::ui::camera::CameraController;
+use crate::ui::cursor::CursorGrabState;
 
-mod level;
 mod target_wall;
+use target_wall::TargetWallPlugin;
 
 pub struct GamePlugin;
 
@@ -10,6 +17,89 @@ impl Plugin for GamePlugin
 {
     fn build(&self, app: &mut App)
     {
-        app.add_plugins(level::LevelPlugin);
+        app.add_plugins(TargetWallPlugin);
+
+        app.add_systems(Startup, setup_level);
+
+        app.add_systems(Update, do_shoot_on_left_click
+            .run_if(in_state(CursorGrabState(true)))
+            .run_if(on_event::<MouseButtonInput>))
+            ;
+    }
+}
+
+fn setup_level(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    const GROUND_SIZE: f32 = 100.0;
+
+    // spawn the camera
+    commands.spawn((
+        CameraController {
+            sensitivity: Vec2::new(0.0007, 0.0007),
+        },
+        Camera3d::default(),
+        Transform::from_xyz(0.0, 1.75, 0.0),
+    ));
+
+    // spawn the ground plane
+    commands.spawn((
+        Mesh3d(meshes.add(Plane3d::new(Vec3::Y, Vec2::splat(GROUND_SIZE * 0.5)))),
+        MeshMaterial3d(materials.add(StandardMaterial {
+            base_color: Color::srgb(0.761, 0.698, 0.502),
+            ..default()
+        })),
+        Transform::IDENTITY,
+        Collider::cuboid(GROUND_SIZE, 0.0, GROUND_SIZE),
+        RigidBody::Static,
+    ));
+
+    // spawn some boxes to shoot at
+    for x in [0.0, 1.5, 3.0]
+    {
+        commands.spawn((
+            Mesh3d(meshes.add(Cuboid::from_corners(
+                Vec3::ZERO, Vec3::ONE,
+            ))),
+            MeshMaterial3d(materials.add(StandardMaterial {
+                base_color: Color::srgb(0.7, 0.1, 0.1),
+                ..default()
+            })),
+            Transform::from_xyz(x, 0.5, -2.0),
+            Collider::cuboid(1.0, 1.0, 1.0),
+            RigidBody::Dynamic,
+        ));
+    }
+
+    // spawn a light source
+    commands.spawn((
+        DirectionalLight {
+            illuminance: light_consts::lux::AMBIENT_DAYLIGHT,
+            shadows_enabled: true,
+            ..default()
+        },
+        Transform::from_xyz(100.0, 200.0, 100.0).looking_at(Vec3::ZERO, Vec3::Y),
+    ));
+}
+
+fn do_shoot_on_left_click(
+    camera_query: Single<&GlobalTransform, With<Camera>>,
+    mut mouse_events: EventReader<MouseButtonInput>,
+    mut projectiles: ResMut<ProjectileSpawner>,
+) {
+    let camera_transform = camera_query.into_inner();
+
+    for _ in mouse_events.read()
+        .filter(|event| event.button == MouseButton::Left)
+        .filter(|event| event.state == ButtonState::Pressed)
+    {
+        projectiles.spawn(ProjectileData {
+            position: camera_transform.translation(),
+            direction: camera_transform.forward(),
+            speed: 900.0,
+            mass: 1.0,
+        });
     }
 }

src/game/target_wall.rs

@@ -1,15 +1,14 @@
 
-use std::collections::HashSet;
+use std::collections::HashMap;
 
 use bevy::prelude::*;
 use avian3d::prelude::*;
 
-use crate::util;
-use crate::physics::Bullet;
+use crate::physics::ProjectileHitEvent;
 
-const TARGET_WALL_SIZE: Vec3 = Vec3::new(20.0, 10.0, 0.1);
-const TARGET_WALL_DISTANCE: f32 = 25.0;
-const TARGET_WALL_COLOR: Color = Color::srgb(0.000, 0.412, 0.580);
+const WALL_SIZE: Vec3 = Vec3::new(20.0, 10.0, 0.1);
+const WALL_FACE_Z: f32 = -25.0;
+const WALL_COLOR: Color = Color::srgb(0.000, 0.412, 0.580);
 
 const TARGET_COUNT: usize = 10;
 const TARGET_RADIUS: f32 = 1.0;
@@ -22,43 +21,99 @@ 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::<CollisionStarted>));
+        app.add_systems(PostProcessCollisions, on_targets_shot.run_if(on_event::<ProjectileHitEvent>));
+    }
+}
+
+#[derive(Component, Copy, Clone, PartialEq, Eq, Hash)]
+struct TargetHandle(i32); // todo: would be nice to use the Entity handle here
+
+#[derive(Resource)]
+struct TargetResources
+{
+    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) - WALL_SIZE.y * 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)]
-struct Target;
+pub struct TargetWall;
 
-impl Target
-{
-    fn random_transform() -> Transform
-    {
-        let x = rand::random::<f32>() * TARGET_WALL_SIZE.x - TARGET_WALL_SIZE.x * 0.5;
-        let y = rand::random::<f32>() * TARGET_WALL_SIZE.y;
-        let scale = rand::random::<f32>() * 0.4 + 0.3;
-
-        Transform::from_xyz(x, y, TARGET_HEIGHT * 0.5 - TARGET_WALL_DISTANCE)
-            .with_scale(Vec3::new(scale, 1.0, scale))
-            .with_rotation(Quat::from_rotation_x(std::f32::consts::PI * 0.5))
-    }
-}
+#[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::new(0.0, 0.0, 0.0), TARGET_WALL_SIZE
+            Vec3::ZERO, WALL_SIZE
         ))),
         MeshMaterial3d(materials.add(StandardMaterial {
-            base_color: TARGET_WALL_COLOR,
+            base_color: WALL_COLOR,
             ..default()
         })),
-        Transform::from_xyz(0.0, TARGET_WALL_SIZE.y * 0.5, -TARGET_WALL_DISTANCE),
-        Collider::cuboid(TARGET_WALL_SIZE.x, TARGET_WALL_SIZE.y, TARGET_WALL_SIZE.z),
+        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,
     ));
 
@@ -74,52 +129,36 @@ fn setup_target_wall(
         TARGET_RADIUS, TARGET_HEIGHT
     );
 
-    for _ in 0..TARGET_COUNT
+    // spawn the targets as children of the wall
+    //
+    (0..TARGET_COUNT).for_each(|_|
     {
-        let transform = Target::random_transform();
+        let handle = target_resources.new_handle();
+        let transform = target_resources.random_transform(&handle);
 
-        commands.spawn((
+        wall_commands.with_child((
             Target,
+            handle,
             Mesh3d(target_mesh.clone()),
             MeshMaterial3d(target_material.clone()),
             transform,
             target_collider.clone(),
             RigidBody::Static,
         ));
-    }
+    });
 }
 
 fn on_targets_shot(
-    mut commands: Commands,
-    mut collision_events: EventReader<CollisionStarted>,
-    mut bullet_query: Query<Entity, With<Bullet>>,
-    mut target_query: Query<&mut Transform, With<Target>>,
+    mut query: Query<(&TargetHandle, &mut Transform), With<Target>>,
+    mut projectile_hit_events: EventReader<ProjectileHitEvent>,
+    mut target_resources: ResMut<TargetResources>,
 ) {
-    let mut bullets_to_despawn = HashSet::with_capacity(8);
-
-    for collision in collision_events.read()
+    for hit_event in projectile_hit_events.read()
     {
-        // resolve the query data from the collision, if the collision is
-        // between a bullet and a target
-        //
-        let Some(bullet_entity) = util::physics::query_collision(&mut bullet_query, collision) else {
-            continue;
-        };
-        let Some(mut target_transform) = util::physics::query_collision(&mut target_query, collision) else {
+        let Ok((handle, mut transform)) = query.get_mut(hit_event.entity) else {
             continue;
         };
 
-        // mark the bullet for despawn
-        bullets_to_despawn.insert(bullet_entity);
-
-        // respawn the target
-        *target_transform = Target::random_transform();
-    }
-
-    // despawn the bullets that were involved in the collisions
-    //
-    for bullet_entity in bullets_to_despawn
-    {
-        commands.entity(bullet_entity).despawn();
+        *transform = target_resources.random_transform(handle);
     }
 }

src/main.rs

@@ -1,27 +1,18 @@
 
+mod util;
+mod ui;
+mod physics;
+mod game;
+
 use bevy::prelude::*;
 
-mod util;
-mod window;
-mod camera;
-mod physics;
-mod player;
-mod ui;
-mod game;
-
-// TODO
-// 1. spawn bullets in front of the player
-// 2. fix the camera position to the player's translation
-
 fn main()
 {
-    let mut app = App::new();
-    app.add_plugins(DefaultPlugins);
-    app.add_plugins(window::WindowPlugin);
-    app.add_plugins(camera::CameraPlugin);
-    app.add_plugins(physics::PhysicsPlugins);
-    app.add_plugins(ui::UiPlugin);
-    app.add_plugins(player::PlayerPlugin);
-    app.add_plugins(game::GamePlugin);
-    app.run();
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_plugins(util::UtilPlugins)
+        .add_plugins(ui::UiPlugins)
+        .add_plugins(physics::PhysicsPlugins)
+        .add_plugins(game::GamePlugin)
+        .run();
 }

src/physics/frame_raycast_anti_ghost.rs

@@ -1,55 +0,0 @@
-
-use bevy::prelude::*;
-use avian3d::prelude::*;
-
-pub struct FrameRaycastAntiGhostPlugin;
-
-impl Plugin for FrameRaycastAntiGhostPlugin
-{
-    fn build(&self, app: &mut App)
-    {
-        app.add_systems(PreUpdate, do_frame_raycast_origin);
-        app.add_systems(PhysicsSchedule, do_frame_raycast_anti_ghost.in_set(PhysicsStepSet::First));
-    }
-}
-
-#[derive(Component)]
-pub struct FrameRaycastAntiGhost;
-
-#[derive(Component)]
-struct FrameRaycastOrigin(Vec3);
-
-fn do_frame_raycast_origin(
-    mut commands: Commands,
-    query: Query<(Entity, &GlobalTransform), With<FrameRaycastAntiGhost>>,
-) {
-    for (entity, transform) in query.iter()
-    {
-        let frame_ray_origin = FrameRaycastOrigin(transform.translation());
-        commands.entity(entity).insert(frame_ray_origin);
-    }
-}
-
-fn do_frame_raycast_anti_ghost(
-    mut query: Query<(Entity, &FrameRaycastOrigin, &mut Transform), With<FrameRaycastAntiGhost>>,
-    ray_caster: SpatialQuery,
-) {
-    for (entity, frame_ray_origin, mut transform) in query.iter_mut()
-    {
-        let ray_origin = frame_ray_origin.0;
-        let ray_direction = transform.translation - ray_origin;
-        let ray_distance = ray_direction.length();
-        let ray_solid = true;
-        let ray_filter = SpatialQueryFilter::default().with_excluded_entities([entity]);
-
-        let Ok(ray_direction) = Dir3::new(ray_direction) else {
-            continue;
-        };
-
-        if let Some(ray_hit) = ray_caster.cast_ray(ray_origin, ray_direction, ray_distance, ray_solid, &ray_filter)
-        {
-            // correct for ghosting by moving the entity to the raycast hit point
-            transform.translation = ray_origin + ray_direction * ray_hit.distance;
-        }
-    }
-}

src/physics/mod.rs

@@ -2,11 +2,8 @@
 use bevy::prelude::*;
 use bevy::app::PluginGroupBuilder;
 
-mod frame_raycast_anti_ghost;
-pub use frame_raycast_anti_ghost::*;
-
-mod projectiles;
-pub use projectiles::*;
+mod projectile;
+pub use projectile::*;
 
 mod world_bounds;
 pub use world_bounds::*;
@@ -15,15 +12,14 @@ pub struct PhysicsPlugins;
 
 impl PluginGroup for PhysicsPlugins
 {
-    fn build(self) -> bevy::app::PluginGroupBuilder
+    fn build(self) -> PluginGroupBuilder
     {
         PluginGroupBuilder::start::<Self>()
 
             .add_group(avian3d::PhysicsPlugins::default())
             .add(avian3d::debug_render::PhysicsDebugPlugin::default())
 
+            .add(ProjectilePlugin)
             .add(WorldBoundsPlugin)
-            .add(FrameRaycastAntiGhostPlugin)
-            .add(ProjectilesPlugin)
     }
 }

src/physics/projectile.rs

@@ -0,0 +1,137 @@
+
+use std::collections::VecDeque;
+
+use bevy::prelude::*;
+use bevy::math::NormedVectorSpace;
+use avian3d::prelude::*;
+
+pub struct ProjectilePlugin;
+
+impl Plugin for ProjectilePlugin
+{
+    fn build(&self, app: &mut App)
+    {
+        app.add_systems(Startup, setup_projectiles);
+
+        app.insert_resource(ProjectileSpawner::default());
+        app.add_systems(PreUpdate, do_projectile_spawn);
+
+        app.add_event::<ProjectileHitEvent>();
+        app.add_systems(PhysicsSchedule, do_projectile_hitscan_flight.in_set(PhysicsStepSet::Last));
+    }
+}
+
+#[derive(Resource)]
+pub struct ProjectileResources
+{
+    pub mesh: Mesh3d,
+    pub material: MeshMaterial3d<StandardMaterial>,
+}
+
+fn setup_projectiles(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    commands.insert_resource(ProjectileResources {
+        mesh: Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 2.0))),
+        material: MeshMaterial3d(materials.add(StandardMaterial {
+            base_color: Color::srgb(0.3, 0.3, 0.3),
+            ..default()
+        })),
+    });
+}
+
+pub struct ProjectileData
+{
+    pub position: Vec3,
+    pub direction: Dir3,
+    pub speed: f32,
+    pub mass: f32,
+}
+
+#[derive(Resource, Default)]
+pub struct ProjectileSpawner
+{
+    queue: VecDeque<ProjectileData>,
+}
+
+impl ProjectileSpawner
+{
+    pub fn spawn(&mut self, data: ProjectileData)
+    {
+        self.queue.push_back(data);
+    }
+}
+
+#[derive(Component)]
+pub struct Projectile;
+
+fn do_projectile_spawn(
+    mut commands: Commands,
+    mut spawner: ResMut<ProjectileSpawner>,
+    resources: Res<ProjectileResources>,
+) {
+    while let Some(spawn_data) = spawner.queue.pop_front()
+    {
+        let rotation = Quat::from_rotation_arc(Vec3::NEG_Z, spawn_data.direction.into());
+        let transform = Transform::from_translation(spawn_data.position).with_rotation(rotation);
+
+        commands.spawn((
+            Projectile,
+            resources.mesh.clone(),
+            resources.material.clone(),
+            transform,
+            LinearVelocity(spawn_data.direction * spawn_data.speed),
+            Mass(spawn_data.mass),
+        ));
+    }
+}
+
+#[derive(Event)]
+#[allow(unused)]
+pub struct ProjectileHitEvent
+{
+    pub entity: Entity,
+    pub normal: Vec3,
+}
+
+fn do_projectile_hitscan_flight(
+    mut commands: Commands,
+    mut query: Query<(Entity, &mut Transform, &LinearVelocity), With<Projectile>>,
+    mut event_writer: EventWriter<ProjectileHitEvent>,
+    spatial_query: SpatialQuery,
+    time: Res<Time>,
+) {
+    for (entity, mut transform, velocity) in query.iter_mut()
+    {
+        let Ok(direction) = Dir3::new(velocity.0) else {
+            continue;
+        };
+
+        let flight_distance = velocity.norm() * time.delta_secs();
+
+        let ray_cast = spatial_query.cast_ray(
+            transform.translation,
+            direction,
+            flight_distance,
+            true,
+            &SpatialQueryFilter::default()
+            );
+
+        let flight_distance = ray_cast.map(|hit| hit.distance).unwrap_or(flight_distance);
+        transform.translation += direction * flight_distance;
+
+        let Some(ray_hit) = ray_cast else {
+            continue;
+        };
+
+        // TODO: impart an impulse on the hit dynamic entity
+
+        event_writer.send(ProjectileHitEvent {
+            entity: ray_hit.entity,
+            normal: ray_hit.normal,
+        });
+        commands.entity(entity).despawn();
+    }
+}

src/physics/projectiles.rs

@@ -1,88 +0,0 @@
-
-use bevy::prelude::*;
-use avian3d::prelude::*;
-
-use super::FrameRaycastAntiGhost;
-
-pub struct ProjectilesPlugin;
-
-impl Plugin for ProjectilesPlugin
-{
-    fn build(&self, app: &mut App)
-    {
-        app.add_systems(Startup, setup_projectiles);
-
-        app.add_event::<BulletFiredEvent>();
-        app.add_systems(Update, on_bullet_fired_event.run_if(on_event::<BulletFiredEvent>));
-    }
-}
-
-#[derive(Resource)]
-pub struct BulletResources
-{
-    pub mesh: Mesh3d,
-    pub material: MeshMaterial3d<StandardMaterial>,
-    pub collider: Collider,
-}
-
-fn setup_projectiles(
-    mut commands: Commands,
-    mut meshes: ResMut<Assets<Mesh>>,
-    mut materials: ResMut<Assets<StandardMaterial>>,
-) {
-    commands.insert_resource(BulletResources {
-        mesh: Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
-        material: MeshMaterial3d(materials.add(StandardMaterial {
-            base_color: Color::srgb(0.7, 0.1, 0.1),
-            ..default()
-        })),
-        collider: Collider::cuboid(1.0, 1.0, 1.0),
-    });
-}
-
-#[derive(Event, Debug)]
-pub struct BulletFiredEvent
-{
-    pub position: Vec3,
-    pub direction: Dir3,
-    pub radius: f32,
-    pub density: f32,
-    pub velocity: f32,
-    pub gyro: f32,
-}
-
-#[derive(Component)]
-pub struct Bullet;
-
-fn on_bullet_fired_event(
-    mut commands: Commands,
-    mut events: EventReader<BulletFiredEvent>,
-    resources: Res<BulletResources>,
-) {
-    for event in events.read()
-    {
-        let rotation = Quat::from_scaled_axis(Vec3::new(
-            rand::random::<f32>() * f32::to_radians(360.0),
-            rand::random::<f32>() * f32::to_radians(360.0),
-            rand::random::<f32>() * f32::to_radians(360.0),
-            ));
-        let transform = Transform::IDENTITY
-            .with_translation(event.position)
-            .with_scale(Vec3::splat(event.radius))
-            .with_rotation(rotation)
-            .looking_to(event.direction, Vec3::Y);
-
-        commands.spawn((
-            Bullet,
-            resources.mesh.clone(),
-            resources.material.clone(),
-            resources.collider.clone(),
-            transform,
-            ColliderDensity(event.density),
-            AngularVelocity(event.gyro * event.direction),
-            RigidBody::Dynamic,
-            FrameRaycastAntiGhost,
-            LinearVelocity(event.velocity * event.direction),
-        ));
-    }
-}

src/player.rs

@@ -1,74 +0,0 @@
-
-use bevy::prelude::*;
-use bevy::window::{CursorGrabMode, PrimaryWindow};
-use bevy::input::{mouse::MouseButtonInput, ButtonState};
-use avian3d::prelude::*;
-
-use crate::camera::CameraController;
-use crate::physics::BulletFiredEvent;
-
-pub struct PlayerPlugin;
-
-impl Plugin for PlayerPlugin
-{
-    fn build(&self, app: &mut App)
-    {
-        app.add_systems(Startup, setup_player);
-        app.add_systems(PreUpdate, do_shoot_on_left_click.run_if(on_event::<MouseButtonInput>));
-    }
-}
-
-#[derive(Component)]
-pub struct Player;
-
-fn setup_player(
-    mut commands: Commands,
-    window: Query<&Window, With<PrimaryWindow>>,
-) {
-    let window = window.single();
-
-    commands
-        .spawn((
-            Player,
-            Transform::from_xyz(0.0, 1.0, 0.0),
-            Collider::capsule(0.5, 1.0),
-            RigidBody::Kinematic,
-            Dominance(32),
-            Visibility::default(),
-        ))
-        .with_child((
-            CameraController {
-                active: window.cursor_options.grab_mode == CursorGrabMode::Locked,
-                sensitivity: Vec2::new(0.0007, 0.0007),
-            },
-            Camera3d::default(),
-            Transform::from_xyz(0.0, 0.75, 0.0),
-        ))
-        ;
-}
-
-fn do_shoot_on_left_click(
-    query: Query<(&GlobalTransform, &CameraController)>,
-    mut mouse_events: EventReader<MouseButtonInput>,
-    mut bullet_events: EventWriter<BulletFiredEvent>,
-) {
-    let (transform, controller) = query.single();
-
-    if ! controller.active {
-        return;
-    }
-
-    for _ in mouse_events.read()
-        .filter(|event| event.button == MouseButton::Left)
-        .filter(|event| event.state == ButtonState::Pressed)
-    {
-        bullet_events.send(BulletFiredEvent {
-            position: transform.translation() + transform.forward() * 0.5,
-            direction: transform.forward(),
-            radius: 0.008,
-            density: 11.0,
-            velocity: 910.0,
-            gyro: f32::to_radians(360.0 * 4.0),
-        });
-    }
-}

src/ui/camera.rs

@@ -3,7 +3,7 @@ use bevy::prelude::*;
 use bevy::input::mouse::{AccumulatedMouseMotion, MouseMotion};
 use bevy::ecs::query::QuerySingleError;
 
-use crate::window::CursorGrabEvent;
+use super::cursor::CursorGrabState;
 
 pub struct CameraPlugin;
 
@@ -11,32 +11,19 @@ impl Plugin for CameraPlugin
 {
     fn build(&self, app: &mut App)
     {
-        app.add_systems(PreUpdate, on_cursor_grab_event.run_if(on_event::<CursorGrabEvent>));
-        app.add_systems(PreUpdate, do_camera_rotation.run_if(on_event::<MouseMotion>));
+        app.add_systems(PreUpdate, do_camera_rotation
+            .run_if(in_state(CursorGrabState(true)))
+            .run_if(on_event::<MouseMotion>)
+            );
     }
 }
 
 #[derive(Component)]
 pub struct CameraController
 {
-    pub active: bool,
     pub sensitivity: Vec2,
 }
 
-fn on_cursor_grab_event(
-    mut query: Query<&mut CameraController>,
-    mut events: EventReader<CursorGrabEvent>,
-) {
-    let Ok(mut controller) = query.get_single_mut() else {
-        return;
-    };
-
-    for CursorGrabEvent(grabbed) in events.read()
-    {
-        controller.active = *grabbed;
-    }
-}
-
 fn do_camera_rotation(
     mut query: Query<(&CameraController, &mut Transform)>,
     mouse_motion: Res<AccumulatedMouseMotion>,
@@ -47,10 +34,6 @@ fn do_camera_rotation(
         Err(QuerySingleError::MultipleEntities(_)) => panic!("Multiple camera controllers found!"),
     };
 
-    if ! controller.active {
-        return;
-    }
-
     if mouse_motion.delta == Vec2::ZERO {
         return;
     }

src/ui/crosshair.rs

@@ -1,6 +1,33 @@
 
 use bevy::prelude::*;
 
+// TODO: add a crosshair component which projects a crosshair to infinity.
+// For now, we'll just draw a crosshair in the center of the screen.
+// This causes a lot of warnings without a camera!
+
+/*
+In bevy 0.15.x, you can automatically insert components based on other components using required components
+https://docs.rs/bevy/latest/bevy/ecs/component/trait.Component.html#required-components
+
+For removal, I would implement it using component hooks
+https://docs.rs/bevy/latest/bevy/ecs/component/struct.ComponentHooks.html
+
+An example where adding or removing A adds or removes B:
+```rust
+#[derive(Component)]
+pub struct B;
+
+#[derive(Component)]
+#[require(B)]
+#[component(on_remove = remove_B)]
+pub struct A;
+
+fn remove_B(world : DefferedWorld, entity : Entity, _id : ComponentId) {
+  world.commands().entity(entity).remove::<B>();
+}
+```
+*/
+
 pub struct CrosshairPlugin;
 
 impl Plugin for CrosshairPlugin

src/ui/cursor.rs

@@ -0,0 +1,54 @@
+
+use bevy::prelude::*;
+use bevy::input::{ButtonState, keyboard::KeyboardInput};
+use bevy::window::{CursorGrabMode, PrimaryWindow};
+
+const CURSOR_TOGGLE_KEY: KeyCode = KeyCode::Escape;
+const CURSOR_TOGGLE_STATE: ButtonState = ButtonState::Released;
+
+pub struct CursorPlugin;
+
+impl Plugin for CursorPlugin
+{
+    fn build(&self, app: &mut App)
+    {
+        app.insert_state(CursorGrabState(false));
+        app.add_systems(PreUpdate, on_cursor_grab_toggled.in_set(CursorSet));
+    }
+}
+
+#[derive(SystemSet, Debug, Copy, Clone, Eq, PartialEq, Hash)]
+struct CursorSet;
+
+#[derive(States, Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct CursorGrabState(pub bool);
+
+fn on_cursor_grab_toggled(
+    mut keyboard_events: EventReader<KeyboardInput>,
+    mut window: Single<&mut Window, With<PrimaryWindow>>,
+    cursor_state: Res<State<CursorGrabState>>,
+    mut next_cursor_state: ResMut<NextState<CursorGrabState>>,
+) {
+    let cursor_toggle_count = keyboard_events.read()
+        .filter(|event| event.key_code == CURSOR_TOGGLE_KEY)
+        .filter(|event| event.state == CURSOR_TOGGLE_STATE)
+        .count();
+
+    if cursor_toggle_count % 2 == 0 {
+        return;
+    }
+
+    match cursor_state.get()
+    {
+        CursorGrabState(true) => {
+            window.cursor_options.visible = false;
+            window.cursor_options.grab_mode = CursorGrabMode::Locked;
+            next_cursor_state.set(CursorGrabState(false));
+        }
+        CursorGrabState(false) => {
+            window.cursor_options.visible = true;
+            window.cursor_options.grab_mode = CursorGrabMode::None;
+            next_cursor_state.set(CursorGrabState(true));
+        }
+    }
+}

src/ui/mod.rs

@@ -1,14 +1,24 @@
 
 use bevy::prelude::*;
+use bevy::app::PluginGroupBuilder;
 
-mod crosshair;
+pub mod window;
+pub mod cursor;
+pub mod camera;
+pub mod crosshair;
 
-pub struct UiPlugin;
+pub struct UiPlugins;
 
-impl Plugin for UiPlugin
+impl PluginGroup for UiPlugins
 {
-    fn build(&self, app: &mut App)
+    fn build(self) -> PluginGroupBuilder
     {
-        app.add_plugins(crosshair::CrosshairPlugin);
+        PluginGroupBuilder::start::<Self>()
+
+            .add(window::WindowPlugin)
+            .add(cursor::CursorPlugin)
+            .add(camera::CameraPlugin)
+
+            .add(crosshair::CrosshairPlugin)
     }
 }

src/ui/window.rs

@@ -0,0 +1,45 @@
+
+use bevy::prelude::*;
+use bevy::window::{CursorGrabMode, PrimaryWindow, WindowResolution};
+
+use super::cursor::CursorGrabState;
+
+pub struct WindowPlugin;
+
+impl Plugin for WindowPlugin
+{
+    fn build(&self, app: &mut App)
+    {
+        app.add_systems(PreStartup, setup_window);
+        app.add_systems(OnEnter(CursorGrabState(true)), on_cursor_grab_toggled);
+        app.add_systems(OnEnter(CursorGrabState(false)), on_cursor_grab_toggled);
+    }
+}
+
+fn setup_window(
+    mut window: Query<&mut Window, With<PrimaryWindow>>,
+) {
+    let mut window = window.single_mut();
+    window.title = "Bevy FPS Game".to_string();
+    window.resolution = WindowResolution::new(1920.0, 1080.0);
+    window.position = WindowPosition::Centered(MonitorSelection::Primary);
+}
+
+fn on_cursor_grab_toggled(
+    mut window: Query<&mut Window, With<PrimaryWindow>>,
+    cursor_state: Res<State<CursorGrabState>>,
+) {
+    let mut window = window.single_mut();
+
+    match cursor_state.get()
+    {
+        CursorGrabState(true) => {
+            window.cursor_options.visible = false;
+            window.cursor_options.grab_mode = CursorGrabMode::Locked;
+        }
+        CursorGrabState(false) => {
+            window.cursor_options.visible = true;
+            window.cursor_options.grab_mode = CursorGrabMode::None;
+        }
+    }
+}

src/util/ecs/despawn_timer.rs

@@ -0,0 +1,30 @@
+
+use bevy::prelude::*;
+
+pub struct DespawnTimerPlugin;
+
+impl Plugin for DespawnTimerPlugin
+{
+    fn build(&self, app: &mut App)
+    {
+        app.add_systems(Update, do_despawn_timer_tick_and_despawn);
+    }
+}
+
+#[derive(Component)]
+pub struct DespawnTimer(pub Timer);
+
+fn do_despawn_timer_tick_and_despawn(
+    mut commands: Commands,
+    mut query: Query<(Entity, &mut DespawnTimer)>,
+    time: Res<Time>,
+) {
+    for (entity, mut timer) in query.iter_mut()
+    {
+        timer.0.tick(time.delta());
+
+        if timer.0.finished() {
+            commands.entity(entity).despawn_recursive();
+        }
+    }
+}

src/util/ecs/mod.rs

@@ -0,0 +1,20 @@
+
+mod despawn_timer;
+pub use despawn_timer::*;
+
+mod path_tracer;
+pub use path_tracer::*;
+
+use bevy::app::{PluginGroup, PluginGroupBuilder};
+
+pub struct UtilEcsPlugins;
+
+impl PluginGroup for UtilEcsPlugins
+{
+    fn build(self) -> bevy::app::PluginGroupBuilder
+    {
+        PluginGroupBuilder::start::<Self>()
+            .add(DespawnTimerPlugin)
+            .add(EntityPathTracerPlugin)
+    }
+}

src/util/ecs/path_tracer.rs

@@ -0,0 +1,156 @@
+
+use std::collections::HashMap;
+
+use bevy::prelude::*;
+use avian3d::prelude::*;
+
+use crate::util::physics::CollisionQuery;
+
+const TRACER_PATH_COLOR:  Color = Color::srgb(0.1, 0.7, 0.1);
+const TRACER_HIT_COLOR_X: Color = Color::srgb(0.7, 0.0, 0.0);
+const TRACER_HIT_COLOR_Y: Color = Color::srgb(0.0, 0.7, 0.0);
+const TRACER_HIT_COLOR_Z: Color = Color::srgb(0.0, 0.0, 0.7);
+const TRACER_HIT_RADIUS: f32 = 0.33;
+
+pub struct EntityPathTracerPlugin;
+
+impl Plugin for EntityPathTracerPlugin
+{
+    fn build(&self, app: &mut App)
+    {
+        app.insert_resource(PathTracerResources {
+            tracers: HashMap::new(),
+        });
+
+        app.add_systems(PhysicsSchedule, do_tracer_log_path.in_set(SolverSet::PreSubstep));
+        app.add_systems(PostProcessCollisions, do_tracer_log_collisions);
+        app.add_systems(Last, do_draw_tracers);
+    }
+}
+
+#[derive(Resource)]
+struct PathTracerResources
+{
+    tracers: HashMap<Entity,PathTraceData>,
+}
+
+#[derive(Default, Clone, PartialEq)]
+pub struct PathTraceData
+{
+    path: Vec<Vec3>,
+    collisions: Vec<Isometry3d>,
+}
+
+impl PathTraceData
+{
+    fn log_position(&mut self, isometry: Isometry3d)
+    {
+        self.path.push(isometry.translation.into());
+    }
+
+    fn log_collision(&mut self, isometry: Isometry3d)
+    {
+        self.collisions.push(isometry);
+    }
+}
+
+#[derive(Component, Clone, PartialEq)]
+#[allow(unused)]
+pub enum PathTracer
+{
+    Transient(PathTraceData),
+    Persistent,
+}
+
+impl Default for PathTracer
+{
+    fn default() -> Self
+    {
+        PathTracer::Transient(PathTraceData {
+            path: Vec::new(),
+            collisions: Vec::new(),
+        })
+    }
+}
+
+impl PathTracer
+{
+    fn mut_trace_data<'a>(
+        &'a mut self,
+        entity: &Entity,
+        resources: &'a mut ResMut<PathTracerResources>
+    ) -> &'a mut PathTraceData
+    {
+        match self {
+            PathTracer::Transient(trace_data) => trace_data,
+            PathTracer::Persistent => resources.tracers.get_mut(entity).unwrap(),
+        }
+    }
+
+    fn get_trace_data<'a>(
+        &'a self,
+        entity: &Entity,
+        resources: &'a Res<PathTracerResources>
+    ) -> &'a PathTraceData
+    {
+        match self {
+            PathTracer::Transient(trace_data) => trace_data,
+            PathTracer::Persistent => resources.tracers.get(entity).unwrap(),
+        }
+    }
+}
+
+fn do_tracer_log_path(
+    mut query: Query<(Entity, &mut PathTracer, &GlobalTransform)>,
+    mut resources: ResMut<PathTracerResources>,
+) {
+    for (entity, mut tracer, transform) in query.iter_mut()
+    {
+        let trace_data = tracer.mut_trace_data(&entity, &mut resources);
+        trace_data.log_position(transform.compute_transform().to_isometry());
+    }
+}
+
+fn do_tracer_log_collisions(
+    mut query: Query<(Entity, &mut PathTracer, &GlobalTransform)>,
+    mut collision_events: EventReader<CollisionStarted>,
+    mut resources: ResMut<PathTracerResources>,
+) {
+    for collision in collision_events.read()
+    {
+        let Ok((entity, mut tracer, transform)) = collision.query_unique(&mut query) else {
+            continue;
+        };
+
+        let trace_data = tracer.mut_trace_data(&entity, &mut resources);
+        trace_data.log_collision(transform.compute_transform().to_isometry());
+    }
+}
+
+fn do_draw_tracers(
+    query: Query<(Entity, &PathTracer)>,
+    resources: Res<PathTracerResources>,
+    mut gizmos: Gizmos,
+) {
+    use std::f32::consts::FRAC_PI_2;
+    let isometry_x = Isometry3d::from_rotation(Quat::from_rotation_x(FRAC_PI_2));
+    let isometry_y = Isometry3d::from_rotation(Quat::from_rotation_y(FRAC_PI_2));
+    let isometry_z = Isometry3d::from_rotation(Quat::from_rotation_z(FRAC_PI_2));
+
+    for (entity, tracer) in query.iter()
+    {
+        let trace_data = tracer.get_trace_data(&entity, &resources);
+
+        for window in trace_data.path.windows(2)
+        {
+            gizmos.line(window[0], window[1], TRACER_PATH_COLOR);
+        }
+
+        for isometry in trace_data.collisions.iter()
+        {
+            gizmos.circle(*isometry * isometry_x, TRACER_HIT_RADIUS, TRACER_HIT_COLOR_X);
+            gizmos.circle(*isometry * isometry_y, TRACER_HIT_RADIUS, TRACER_HIT_COLOR_Y);
+            gizmos.circle(*isometry * isometry_z, TRACER_HIT_RADIUS, TRACER_HIT_COLOR_Z);
+        }
+    }
+}

src/util/mod.rs

@@ -1,2 +1,21 @@
 
+use bevy::app::{PluginGroup, PluginGroupBuilder};
+
+pub mod ecs;
+use ecs::UtilEcsPlugins;
+
 pub mod physics;
+use physics::UtilPhysicsPlugins;
+
+pub struct UtilPlugins;
+
+impl PluginGroup for UtilPlugins
+{
+    fn build(self) -> bevy::app::PluginGroupBuilder
+    {
+        PluginGroupBuilder::start::<Self>()
+
+            .add_group(UtilEcsPlugins)
+            .add_group(UtilPhysicsPlugins)
+    }
+}

src/util/physics.rs

@@ -1,16 +0,0 @@
-
-use bevy::prelude::*;
-use bevy::ecs::query::{QueryData, QueryFilter, QueryItem};
-use avian3d::prelude::*;
-
-pub fn query_collision<'a,D,F>(query: &'a mut Query<D,F>, collision: &CollisionStarted)
-    -> Option<QueryItem<'a, D>>
-where
-    D: QueryData,
-    F: QueryFilter,
-{
-    let CollisionStarted(entity1, entity2) = collision;
-    if query.contains(*entity1) { return query.get_mut(*entity1).ok(); }
-    if query.contains(*entity2) { return query.get_mut(*entity2).ok(); }
-    None
-}

src/util/physics/collision_query.rs

@@ -0,0 +1,86 @@
+
+use bevy::prelude::*;
+use bevy::ecs::query::{QueryData, QueryEntityError, QueryFilter, QueryItem};
+use avian3d::prelude::*;
+
+/// A trait that provides a method to retrieve the two entities involved in a collision.
+///
+pub trait ToCollisionEntities
+{
+    /// Returns the two entities involved in this collision.
+    ///
+    fn to_collision_entities(&self) -> (Entity, Entity);
+}
+
+impl ToCollisionEntities for Collision {
+    fn to_collision_entities(&self) -> (Entity, Entity) {
+        (self.0.entity1, self.0.entity2)
+    }
+}
+
+impl ToCollisionEntities for CollisionStarted {
+    fn to_collision_entities(&self) -> (Entity, Entity) {
+        (self.0, self.1)
+    }
+}
+
+impl ToCollisionEntities for CollisionEnded {
+    fn to_collision_entities(&self) -> (Entity, Entity) {
+        (self.0, self.1)
+    }
+}
+
+/// Represents errors that can occur when querying collision data.
+///
+pub enum CollisionQueryError<'w>
+{
+    /// Indicates that both collision entities match the query.
+    CollisionQueryNotUnique,
+    /// Indicates that neither collision entity matches the query.
+    NoMatchingCollisionEntity,
+    /// Indicates that an error occurred during the query.
+    QueryError(#[allow(unused)] QueryEntityError<'w>),
+}
+
+pub trait CollisionQuery
+{
+    /// Queries the collision data for the unique entity associated with this collision query.
+    ///
+    /// # Parameters
+    /// - `query`: A mutable reference to the query to search for the collision entities.
+    ///
+    /// # Returns
+    /// - `Ok(QueryItem<D>)`: The query item for the found unique collision entity.
+    /// - `Err(CollisionQueryError::CollisionQueryNotUnique)`: If both collision entities match the query.
+    /// - `Err(CollisionQueryError::NoMatchingCollisionEntity)`: If neither collision entity matches the query.
+    /// - `Err(CollisionQueryError::QueryError)`: If an error occurs during the query.
+    ///
+    fn query_unique<'a,'w,D,F>(&self, query: &'a mut Query<D,F>)
+        -> Result<QueryItem<'w, D>,CollisionQueryError<'w>>
+    where
+        'a: 'w,
+        D: QueryData,
+        F: QueryFilter,
+        ;
+}
+
+impl<T> CollisionQuery for T where T: ToCollisionEntities
+{
+    fn query_unique<'a,'w,D,F>(&self, query: &'a mut Query<D,F>)
+        -> Result<QueryItem<'w, D>,CollisionQueryError<'w>>
+    where
+        'a: 'w,
+        D: QueryData,
+        F: QueryFilter,
+    {
+        let (entity1, entity2) = self.to_collision_entities();
+
+        match (query.contains(entity1), query.contains(entity2))
+        {
+            (true, true) => Err(CollisionQueryError::CollisionQueryNotUnique),
+            (true, false) => query.get_mut(entity1).map_err(|error| CollisionQueryError::QueryError(error)),
+            (false, true) => query.get_mut(entity2).map_err(|error| CollisionQueryError::QueryError(error)),
+            (false, false) => Err(CollisionQueryError::NoMatchingCollisionEntity),
+        }
+    }
+}

src/util/physics/mod.rs

@@ -0,0 +1,15 @@
+
+use bevy::app::{PluginGroup, PluginGroupBuilder};
+
+mod collision_query;
+pub use collision_query::*;
+
+pub struct UtilPhysicsPlugins;
+
+impl PluginGroup for UtilPhysicsPlugins
+{
+    fn build(self) -> PluginGroupBuilder
+    {
+        PluginGroupBuilder::start::<Self>()
+    }
+}

src/window.rs

@@ -1,57 +0,0 @@
-
-use bevy::prelude::*;
-use bevy::window::{CursorGrabMode, PrimaryWindow, WindowResolution};
-use bevy::input::{ButtonState, keyboard::KeyboardInput};
-
-pub struct WindowPlugin;
-
-impl Plugin for WindowPlugin
-{
-    fn build(&self, app: &mut App)
-    {
-        app.add_systems(PreStartup, setup_window);
-
-        app.add_event::<CursorGrabEvent>();
-        app.add_systems(PreUpdate, on_cursor_grab_toggled.run_if(on_event::<KeyboardInput>));
-    }
-}
-
-#[derive(Event)]
-pub struct CursorGrabEvent(pub bool);
-
-fn setup_window(
-    mut window: Query<&mut Window, With<PrimaryWindow>>,
-) {
-    let mut window = window.single_mut();
-    window.title = "Bevy FPS Game".to_string();
-    window.resolution = WindowResolution::new(1920.0, 1080.0);
-    window.position = WindowPosition::Centered(MonitorSelection::Primary);
-}
-
-fn on_cursor_grab_toggled(
-    mut window: Query<&mut Window, With<PrimaryWindow>>,
-    mut events: EventReader<KeyboardInput>,
-    mut cursor_events: EventWriter<CursorGrabEvent>,
-) {
-    let mut window = window.single_mut();
-
-    for _ in events.read()
-        .filter(|event| event.key_code == KeyCode::Escape)
-        .filter(|event| event.state == ButtonState::Pressed)
-    {
-        match window.cursor_options.grab_mode
-        {
-            CursorGrabMode::None => {
-                window.cursor_options.visible = false;
-                window.cursor_options.grab_mode = CursorGrabMode::Locked;
-                cursor_events.send(CursorGrabEvent(true));
-            }
-            CursorGrabMode::Locked => {
-                window.cursor_options.visible = true;
-                window.cursor_options.grab_mode = CursorGrabMode::None;
-                cursor_events.send(CursorGrabEvent(false));
-            }
-            _ => panic!("Invalid cursor grab mode"),
-        }
-    }
-}