Begin work on a main menu & UI systems

client/src/main.rs

@@ -8,10 +8,21 @@ use bevy::{
 use thiserror::Error;
 use tungstenite::{WebSocket, http::Response, stream::MaybeTlsStream};
 
+use crate::ui::{despawn_main_menu, spawn_main_menu};
+
+mod ui;
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
-        .add_systems(Startup, setup)
+        .insert_state(GameState::MainMenu)
+        .add_systems(Startup, spawn_camera)
+        .add_systems(OnEnter(GameState::MainMenu), spawn_main_menu)
+        .add_systems(OnExit(GameState::MainMenu), despawn_main_menu)
+        .add_observer(ui::button_hover_start)
+        .add_observer(ui::button_hover_stop)
+        // TODO: System to operate buttons & other UI widgets
+        // .add_systems(Update, )
         .add_systems(
             Update,
             (
@@ -20,7 +31,8 @@ fn main() {
                 handle_tasks,
                 send_info,
                 recv_info,
-            ),
+            )
+                .run_if(in_state(GameState::ConnectionDemo)),
         )
         .add_message::<WebSocketConnectionMessage>()
         .insert_resource(ChatTimer {
@@ -29,6 +41,29 @@ fn main() {
         .run();
 }
 
+/// Main game state indicator
+#[derive(Debug, Hash, PartialEq, Eq, Clone, States)]
+enum GameState {
+    MainMenu,
+    Playing,
+    ConnectionDemo, // TODO: Remove this state.
+}
+
+/// Utility to despawn entities with a given component. Useful for scene
+/// changes.
+///
+/// I'm using this primarily with marker components to delete UI elements when
+/// they are no longer needed. E.g.: Removing the main menu after starting.
+pub fn despawn<T: Component>(mut commands: Commands, targets: Query<Entity, With<T>>) {
+    targets
+        .iter()
+        .for_each(|entt| commands.entity(entt).despawn());
+}
+
+fn spawn_camera(mut commands: Commands) {
+    commands.spawn(Camera2d);
+}
+
 /// Initialize the scene
 fn setup(
     mut commands: Commands,