Spawn the gameplay elements

Now to start wiring them in for basic operation, then to pipe it all
through the WebSocket.

client/src/main.rs

@@ -12,6 +12,8 @@ use crate::ui::{despawn_main_menu, spawn_main_menu};
 
 mod ui;
 
+const PADDLE_GAP: f32 = 20.0; // gap between the paddles and the wall (window border)
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
@@ -23,6 +25,7 @@ fn main() {
         .add_observer(ui::button_hover_stop)
         // TODO: System to operate buttons & other UI widgets
         // .add_systems(Update, )
+        .add_systems(OnEnter(GameState::Playing), setup_game)
         .add_systems(
             Update,
             (
@@ -65,17 +68,38 @@ fn spawn_camera(mut commands: Commands) {
 }
 
 /// Initialize the scene
-fn setup(
+fn setup_game(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ColorMaterial>>,
+    window: Single<&Window>,
 ) {
-    commands.spawn(Camera2d);
+    // ball
     commands.spawn((
         Mesh2d(meshes.add(Circle::new(10.0))),
         MeshMaterial2d(materials.add(Color::srgb(1.0, 0.0, 0.0))),
         Transform::default(),
     ));
+
+    let paddle_mesh = meshes.add(Rectangle::new(10.0, 100.0));
+    let paddle_material = materials.add(Color::WHITE);
+    // Player 1
+    commands.spawn((
+        // TODO: Marker component for player
+        // Maybe one for each player?
+        // Maybe it can hold the WebSocket, too.
+        // *Maybe* I can have one struct with an Option<Ws> to know which
+        //   player is the local one (the one with a socket).
+        Mesh2d(paddle_mesh.clone()),
+        MeshMaterial2d(paddle_material.clone()),
+        Transform::from_xyz(-window.width() / 2.0 + PADDLE_GAP, 0.0, 1.0),
+    ));
+    // Player 2
+    commands.spawn((
+        Mesh2d(paddle_mesh),
+        MeshMaterial2d(paddle_material),
+        Transform::from_xyz(window.width() / 2.0 - PADDLE_GAP, 0.0, 1.0),
+    ));
 }
 
 /// ECS Component to hold the WebSocket. I guess there's going to be a magic