Dummy ship, single input, and motion integrator

The ship, such as it is, exists and moves when the player presses "W".

Position is updated according to velocity, and the mesh transform is
updated to match the position.

src/lib.rs

@@ -0,0 +1,94 @@
+mod config;
+
+use crate::config::{BACKGROUND_COLOR, PLAYER_SHIP_COLOR};
+
+use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
+
+pub struct AsteroidPlugin;
+
+impl Plugin for AsteroidPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(Startup, (spawn_camera, spawn_player))
+            .insert_resource(ClearColor(BACKGROUND_COLOR))
+            .add_systems(FixedUpdate, input_ship_thruster)
+            // .add_systems(FixedUpdate, input_ship_rotation);
+            .add_systems(FixedPostUpdate, (integrate_velocity, update_positions));
+    }
+}
+
+#[derive(Component)]
+struct Position(bevy::math::Vec2);
+
+#[derive(Component)]
+struct Velocity(bevy::math::Vec2);
+
+#[derive(Component)]
+struct Rotation(bevy::prelude::Quat);
+
+#[derive(Component)]
+struct Ship;
+
+fn spawn_camera(mut commands: Commands) {
+    commands.spawn(Camera2dBundle::default());
+}
+
+fn spawn_player(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<ColorMaterial>>,
+) {
+    commands.spawn((
+        Ship,
+        Position(Vec2::default()),
+        Velocity(Vec2::ZERO),
+        MaterialMesh2dBundle {
+            mesh: meshes.add(Circle::new(10.0)).into(),
+            material: materials.add(PLAYER_SHIP_COLOR),
+            transform: Transform::default(),
+            ..default()
+        },
+    ));
+}
+
+/*
+ Checks if "W" is pressed and increases velocity accordingly.
+*/
+fn input_ship_thruster(
+    keyboard_input: Res<ButtonInput<KeyCode>>,
+    mut query: Query<&mut Velocity, With<Ship>>,
+) {
+    let Ok(mut velocity) = query.get_single_mut() else {
+        let count = query.iter().count();
+        panic!("There should be exactly one player ship! Instead, there seem to be {count}.");
+    };
+
+    if keyboard_input.pressed(KeyCode::KeyW) {
+        velocity.0 += Vec2::new(10.0, 0.0);
+    }
+}
+
+/*
+ Checks if "A" or "D" is pressed and rotates the ship accordingly
+*/
+fn input_ship_rotation(
+    keyboard_input: Res<ButtonInput<KeyCode>>,
+    mut query: Query<&mut Rotation, With<Ship>>,
+) {
+    todo!();
+}
+
+/*
+ Add velocity to position
+*/
+fn integrate_velocity(mut query: Query<(&mut Position, &Velocity)>, time: Res<Time>) {
+    for (mut position, velocity) in &mut query {
+        position.0 += velocity.0 * time.delta_seconds();
+    }
+}
+
+fn update_positions(mut query: Query<(&mut Transform, &Position)>) {
+    for (mut transform, position) in &mut query {
+        transform.translation.x = position.0.x;
+        transform.translation.y = position.0.y;
+    }
+}