Finish main-menu button handling

I'm stealing the game-over plugin's button handling for use in the main
menu. I guess it turns out that my widgets are more generic than
intended.

src/lib.rs

@@ -81,7 +81,7 @@ impl Plugin for AsteroidPlugin {
         .add_event::<events::AsteroidDestroy>()
         .add_event::<events::ShipDestroy>()
         .add_event::<events::BulletDestroy>();
-        app.insert_state(GameState::GameOver);
+        app.insert_state(GameState::TitleScreen);
     }
 }
 

src/widgets.rs

@@ -15,10 +15,10 @@ pub struct PluginGameMenu;
 impl Plugin for PluginGameMenu {
     fn build(&self, app: &mut App) {
         app.add_systems(OnEnter(GameState::TitleScreen), spawn_menu)
-            .add_systems(OnExit(GameState::TitleScreen), despawn::<TitleUI>)
+            .add_systems(OnExit(GameState::TitleScreen), despawn::<MarkerMainMenu>)
             .add_systems(
                 Update,
-                handle_spacebar.run_if(in_state(GameState::TitleScreen)),
+                (handle_spacebar, operate_buttons).run_if(in_state(GameState::TitleScreen)),
             );
     }
 }
@@ -38,7 +38,7 @@ impl Plugin for PluginGetReady {
     }
 }
 
-/// Plugin for the game-over screen (TODO)
+/// Plugin for the game-over screen
 pub struct PluginGameOver;
 
 impl Plugin for PluginGameOver {
@@ -47,11 +47,16 @@ impl Plugin for PluginGameOver {
             .add_systems(OnExit(GameState::GameOver), despawn::<MarkerGameOver>)
             .add_systems(
                 Update,
-                operate_gameover_ui.run_if(in_state(GameState::GameOver)),
+                operate_buttons.run_if(in_state(GameState::GameOver)),
             );
     }
 }
 
+// Marker component for the title screen UI entity.
+// This way, a query for the TitleUI can be used to despawn the title screen
+#[derive(Component)]
+struct MarkerMainMenu;
+
 /// Marker component for things on the get-ready indicator
 #[derive(Component)]
 struct OnReadySetGo;
@@ -65,8 +70,9 @@ struct MarkerGameOver;
 /// Attach this component to a button and [`PluginGameOver`] will use it to
 /// decide what to do when that button is pressed.
 #[derive(Component)]
-enum GameOverMenuAction {
+enum ButtonMenuAction {
     ToMainMenu,
+    StartGame,
     Quit,
 }
 
@@ -90,6 +96,62 @@ fn despawn<T: Component>(mut commands: Commands, to_despawn: Query<Entity, With<
     }
 }
 
+/// Utility function for creating a standard button.
+fn button_bundle(text: &str) -> impl Bundle {
+    (
+        Button,
+        // TODO: Generic action
+        Node {
+            width: Val::Px(150.0),
+            height: Val::Px(65.0),
+            border: UiRect::all(Val::Px(2.0)),
+            justify_content: JustifyContent::Center,
+            align_items: AlignItems::Center,
+            margin: UiRect::all(Val::Px(5.0)),
+            ..default()
+        },
+        BorderColor(Color::BLACK),
+        BorderRadius::MAX,
+        BackgroundColor(UI_BUTTON_NORMAL),
+        children![(
+            Text::new(text),
+            TextColor(Color::srgb(0.9, 0.9, 0.9)),
+            TextShadow::default(),
+        )],
+    )
+}
+
+fn spawn_menu(mut commands: Commands) {
+    commands
+        .spawn((
+            MarkerMainMenu,
+            Node {
+                width: Val::Percent(100.0),
+                height: Val::Percent(100.0),
+                align_items: AlignItems::Center,
+                justify_content: JustifyContent::Center,
+                flex_direction: FlexDirection::Column,
+                ..Default::default()
+            },
+        ))
+        .with_children(|cmds| {
+            cmds.spawn((
+                Text::new("Robert's Bad Asteroids Game"),
+                TextFont::from_font_size(50.0),
+                TextLayout::new_with_justify(JustifyText::Center),
+                TextShadow::default(),
+            ));
+            cmds.spawn((
+                Text::new("Press space to begin"),
+                TextFont::from_font_size(20.0),
+                TextColor(Color::srgb(0.7, 0.7, 0.7)),
+                TextShadow::default(),
+            ));
+            cmds.spawn((button_bundle("Start Game"), ButtonMenuAction::StartGame));
+            cmds.spawn((button_bundle("Quit"), ButtonMenuAction::Quit));
+        });
+}
+
 fn spawn_get_ready(mut commands: Commands) {
     commands.spawn((
         OnReadySetGo, // marker, so this can be de-spawned properly
@@ -139,48 +201,8 @@ fn spawn_gameover_ui(mut commands: Commands) {
             ..default()
         },
         children![
-            (
-                Button,
-                GameOverMenuAction::ToMainMenu,
-                Node {
-                    width: Val::Px(150.0),
-                    height: Val::Px(65.0),
-                    border: UiRect::all(Val::Px(2.0)),
-                    justify_content: JustifyContent::Center,
-                    align_items: AlignItems::Center,
-                    margin: UiRect::all(Val::Px(5.0)),
-                    ..default()
-                },
-                BorderColor(Color::BLACK),
-                BorderRadius::MAX,
-                BackgroundColor(UI_BUTTON_NORMAL),
-                children![(
-                    Text::new("Main Menu"),
-                    TextColor(Color::srgb(0.9, 0.9, 0.9)),
-                    TextShadow::default(),
-                )]
-            ),
-            (
-                Button,
-                GameOverMenuAction::Quit,
-                Node {
-                    width: Val::Px(150.0),
-                    height: Val::Px(65.0),
-                    border: UiRect::all(Val::Px(2.0)),
-                    justify_content: JustifyContent::Center,
-                    align_items: AlignItems::Center,
-                    margin: UiRect::all(Val::Px(5.0)),
-                    ..default()
-                },
-                BorderColor(Color::BLACK),
-                BorderRadius::MAX,
-                BackgroundColor(UI_BUTTON_NORMAL),
-                children![(
-                    Text::new("Quit"),
-                    TextColor(Color::srgb(0.9, 0.9, 0.9)),
-                    TextShadow::default(),
-                )]
-            )
+            (button_bundle("Main Menu"), ButtonMenuAction::ToMainMenu,),
+            (button_bundle("Quit"), ButtonMenuAction::Quit),
         ],
     ));
 }
@@ -210,19 +232,24 @@ fn animate_get_ready_widget(
     }
 }
 
-/// Handles interaction and performs updates to the game-over UI.
+/// Handles interactions with the menu buttons.
 ///
-/// Used by [`PluginGameOver`] while in the [`GameState::GameOver`] state.
+/// The buttons are used by the main menu and the game-over menu to change
+/// between game states.
 ///
-/// Mostly a button input handler, but it also makes for a convenient single
-/// place to keep all system logic for this plugin.
-fn operate_gameover_ui(
+/// Button animation and action handling is done entirely within this system.
+///
+/// There are no checks for current state. If a "quit" button was put somewhere
+/// on the HUD, this system would quit the game. The same will happen for
+/// returning to the title screen. This should be useful for making a pause
+/// menu, too.
+fn operate_buttons(
     mut interactions: Query<
         (
             &Interaction,
             &mut BackgroundColor,
             &mut BorderColor,
-            &GameOverMenuAction,
+            &ButtonMenuAction,
         ),
         (Changed<Interaction>, With<Button>),
     >,
@@ -236,10 +263,13 @@ fn operate_gameover_ui(
                 *color = UI_BUTTON_PRESSED.into();
                 border_color.0 = RED.into();
                 match menu_action {
-                    GameOverMenuAction::ToMainMenu => {
+                    ButtonMenuAction::ToMainMenu => {
                         game_state.set(GameState::TitleScreen);
                     }
-                    GameOverMenuAction::Quit => {
+                    ButtonMenuAction::StartGame => {
+                        game_state.set(GameState::Playing);
+                    }
+                    ButtonMenuAction::Quit => {
                         app_exit_events.write(AppExit::Success);
                     }
                 }
@@ -256,32 +286,7 @@ fn operate_gameover_ui(
     }
 }
 
-// Marker component for the title screen UI entity.
-// This way, a query for the TitleUI can be used to despawn the title screen
-#[derive(Component)]
-struct TitleUI;
-
-fn spawn_menu(mut commands: Commands) {
-    commands
-        .spawn((
-            TitleUI,
-            Node {
-                flex_direction: FlexDirection::Column,
-                ..Default::default()
-            },
-        ))
-        .with_children(|cmds| {
-            cmds.spawn((
-                Text::new("Robert's Bad Asteroids Game"),
-                TextFont::from_font_size(50.0),
-            ));
-            cmds.spawn((
-                Text::new("Press space to begin"),
-                TextFont::from_font_size(40.0),
-            ));
-        });
-}
-
+/// Main menu input listener. Starts game when the spacebar is pressed.
 fn handle_spacebar(input: Res<ButtonInput<KeyCode>>, mut game_state: ResMut<NextState<GameState>>) {
     if input.just_pressed(KeyCode::Space) {
         game_state.set(GameState::GetReady);