Camera follows selected character

src/game.rs

@@ -32,9 +32,14 @@ impl Plugin for GamePlugin {
 			.add_system_set(
 				SystemSet::on_update(AppState::Game)
 					.with_system(crate::levels::post_setup_level)
-					.with_system(keyboard_input_system),
+					.with_system(keyboard_input_system)
+					.with_system(move_camera),
+			)
+			.add_system_set(
+				SystemSet::on_update(AppState::Win)
+					.with_system(keyboard_input_system)
+					.with_system(move_camera),
 			)
-			.add_system_set(SystemSet::on_update(AppState::Win).with_system(keyboard_input_system))
 			.add_system_to_stage(CoreStage::PostUpdate, collision_event_system);
 	}
 }
@@ -88,12 +93,14 @@ fn setup(
 	mut commands: Commands,
 	mut current_level: ResMut<CurrentLevel>,
 	mut level_startup_event: EventWriter<LevelStartupEvent>,
+	mut camera_query: Query<&mut Transform, With<Camera>>,
 ) {
 	let level_id = LevelId(current_level.0.map_or(0, |level_id| level_id.0 + 1));
 	crate::levels::setup_level(
 		&mut commands,
 		&mut current_level,
 		&mut level_startup_event,
+		&mut camera_query,
 		level_id,
 	);
 }
@@ -343,3 +350,40 @@ fn win_setup(mut commands: Commands, asset_server: Res<AssetServer>) {
 		})
 		.insert(Level);
 }
+
+fn move_camera(
+	mut camera_query: Query<(&Camera, &mut Transform, &GlobalTransform)>,
+	characters: Query<(&CharacterId, &Transform), Without<Camera>>,
+	level_query: Query<&SelectedCharacterId>,
+) {
+	const MARGIN: f32 = 128.0;
+
+	if let Ok(selected_character_id) = level_query.get_single() {
+		if let Some(selected_character_id) = &selected_character_id.0 {
+			if let Some((_character_id, transform)) = characters
+				.iter()
+				.find(|(character_id, _transform)| *character_id == selected_character_id)
+			{
+				let (camera, mut camera_transform, camera_global_transform) =
+					camera_query.single_mut();
+
+				let pos = camera
+					.world_to_viewport(camera_global_transform, transform.translation)
+					.unwrap();
+				let size = camera.logical_viewport_size().unwrap();
+				if pos.x < MARGIN {
+					camera_transform.translation.x += pos.x - MARGIN;
+				}
+				if pos.x > size.x - MARGIN {
+					camera_transform.translation.x += MARGIN + pos.x - size.x;
+				}
+				if pos.y < MARGIN {
+					camera_transform.translation.y += pos.y - MARGIN;
+				}
+				if pos.y > size.y - MARGIN {
+					camera_transform.translation.y += MARGIN + pos.y - size.y;
+				}
+			}
+		}
+	}
+}

src/levels.rs

@@ -14,6 +14,7 @@ pub fn setup_level(
 	commands: &mut Commands,
 	current_level: &mut ResMut<CurrentLevel>,
 	level_startup_event: &mut EventWriter<LevelStartupEvent>,
+	camera_query: &mut Query<&mut Transform, With<Camera>>,
 	level_id: LevelId,
 ) {
 	let level_entity = commands
@@ -24,6 +25,8 @@ pub fn setup_level(
 		.id();
 	current_level.0 = Some(level_id);
 
+	camera_query.single_mut().translation = Default::default();
+
 	level_startup_event.send(LevelStartupEvent(level_entity));
 }