Simple ai shooting PoC (#23)

src/aim/marker.rs

@@ -0,0 +1,60 @@
+use crate::{GameState, loading_assets::UIAssets, utils::billboards::Billboard};
+use bevy::prelude::*;
+use bevy_sprite3d::{Sprite3dBuilder, Sprite3dParams};
+use ops::sin;
+
+#[derive(Component, Reflect)]
+#[reflect(Component)]
+struct TargetMarker;
+
+#[derive(Event)]
+pub enum MarkerEvent {
+    Spawn(Entity),
+    Despawn,
+}
+
+pub fn plugin(app: &mut App) {
+    app.add_systems(Update, move_marker.run_if(in_state(GameState::Playing)));
+    app.add_observer(marker_event);
+}
+
+fn move_marker(mut query: Query<&mut Transform, With<TargetMarker>>, time: Res<Time>) {
+    for mut transform in query.iter_mut() {
+        transform.translation = Vec3::new(0., 3. + (sin(time.elapsed_secs() * 6.) * 0.2), 0.);
+    }
+}
+
+fn marker_event(
+    trigger: Trigger<MarkerEvent>,
+    mut commands: Commands,
+    assets: Res<UIAssets>,
+    mut sprite_params: Sprite3dParams,
+    marker: Query<Entity, With<TargetMarker>>,
+) {
+    for m in marker.iter() {
+        commands.entity(m).despawn_recursive();
+    }
+
+    let MarkerEvent::Spawn(target) = trigger.event() else {
+        return;
+    };
+
+    let id = commands
+        .spawn((
+            Name::new("aim-marker"),
+            Billboard,
+            TargetMarker,
+            Transform::default(),
+            Sprite3dBuilder {
+                image: assets.head_selector.clone(),
+                pixels_per_metre: 30.,
+                alpha_mode: AlphaMode::Blend,
+                unlit: true,
+                ..default()
+            }
+            .bundle(&mut sprite_params),
+        ))
+        .id();
+
+    commands.entity(*target).add_child(id);
+}