Add most of a "CloseButton" widget

I'm trying out a new scope strategy. The CloseButton exists as a real
struct with the `Component` trait. There's a bundle spawning utility
function and several observer systems. The observer systems have been
added directly to the app, which I *believe* means they won't be
duplicated the way the Big Red Button's observers will.

src/main.rs

@@ -30,6 +30,10 @@ fn main() {
         RotatingMachine::spawn_rotator_machine_ui,
       ),
     )
+    .add_observer(widgets::CloseButton::hover_start)
+    .add_observer(widgets::CloseButton::hover_stop)
+    .add_observer(widgets::CloseButton::press_start)
+    .add_observer(widgets::CloseButton::press_stop)
     .run();
 }
 

src/resources.rs

@@ -17,6 +17,17 @@ pub struct UiTheme {
   // pressed
   pub brb_pressed_bg: Color,
   pub brb_pressed_border: Color,
+
+  // Colors for low-priority buttons
+  // normal
+  pub quiet_bg: Color,
+  pub quiet_border: Color,
+  // hover
+  pub quiet_hover_bg: Color,
+  pub quiet_hover_border: Color,
+  // pressed
+  pub quiet_pressed_bg: Color,
+  pub quiet_pressed_border: Color,
 }
 
 impl FromWorld for UiTheme {
@@ -28,6 +39,13 @@ impl FromWorld for UiTheme {
       brb_hover_border: RED.into(),
       brb_pressed_bg: GREEN.into(),
       brb_pressed_border: DARK_GREEN.into(),
+
+      quiet_bg: GRAY.into(),
+      quiet_border: DARK_GRAY.into(),
+      quiet_hover_bg: DARK_GRAY.into(),
+      quiet_hover_border: LIGHT_GRAY.into(),
+      quiet_pressed_bg: LIGHT_GRAY.into(),
+      quiet_pressed_border: GRAY.into(),
     }
   }
 }

src/widgets/mod.rs

@@ -38,11 +38,12 @@ fn machine_ui_base(header: impl Into<String>) -> impl Bundle {
     },
     BackgroundColor(SLATE_100.into()),
     BorderRadius::all(Percent(2.0)),
-    children![(
+    children![
+      (
         // TODO: A real node with stuff in it (buttons, maybe?)
         Node {
           justify_content: JustifyContent::Center,
-        grid_column: GridPlacement::span(3),
+          grid_column: GridPlacement::span(2),
           ..default()
         },
         BackgroundColor(RED.into()),
@@ -52,7 +53,9 @@ fn machine_ui_base(header: impl Into<String>) -> impl Bundle {
           TextColor(BLACK.into()),
           // TODO: Text shadow, maybe. I couldn't make it look good.
         )],
-    )],
+      ),
+      CloseButton::bundle(),
+    ],
   )
 }
 
@@ -138,3 +141,85 @@ fn button_press_stop(
     border.0 = ui_theme.brb_border;
   }
 }
+
+/// Button marker for closing (despawning) an in-game menu entity.
+#[derive(Component)]
+#[require(Button)]
+pub struct CloseButton;
+
+impl CloseButton {
+  /// Spawn a button that will despawn the top-most node when pressed.
+  fn bundle() -> impl Bundle {
+    (
+      CloseButton,
+      Node {
+        width: Px(20.0),
+        height: Px(20.0),
+        aspect_ratio: Some(1.0),
+        align_items: AlignItems::Center,
+        justify_content: JustifyContent::Center,
+        border: UiRect::all(Px(1.0)),
+        ..Default::default()
+      },
+      // TODO: Get colors *somehow.*
+      // - Turn this function into a Bevy System, require `Res<...>`
+      // - Just pass in the colors, let the caller figure out sourcing them.
+      BackgroundColor(GRAY.into()),
+      BorderColor(DARK_GRAY.into()),
+      BorderRadius::all(Px(2.0)),
+      children![(
+        // TODO: Replace with an icon/sprite
+        Text::new("X"),
+        TextColor(BLACK.into()),
+      )],
+    )
+  }
+
+  pub fn hover_start(
+    event: Trigger<Pointer<Over>>,
+    // Get button background and border colors so we can change them.
+    // Filter for *changed* interactions, and only entities with a [`Button`]
+    mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
+    ui_theme: Res<UiTheme>,
+  ) {
+    // Get the components for only the Trigger's target entity
+    if let Ok((mut bg, mut border)) = button_colors.get_mut(event.target()) {
+      bg.0 = ui_theme.quiet_hover_bg;
+      border.0 = ui_theme.quiet_hover_border;
+    }
+  }
+
+  pub fn hover_stop(
+    event: Trigger<Pointer<Out>>,
+    mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
+    ui_theme: Res<UiTheme>,
+  ) {
+    if let Ok((mut bg, mut border)) = button_colors.get_mut(event.target()) {
+      bg.0 = ui_theme.quiet_bg;
+      border.0 = ui_theme.quiet_border;
+    }
+  }
+
+  pub fn press_start(
+    event: Trigger<Pointer<Pressed>>,
+    mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
+    ui_theme: Res<UiTheme>,
+  ) {
+    if let Ok((mut bg, mut border)) = button_colors.get_mut(event.target()) {
+      bg.0 = ui_theme.quiet_pressed_bg;
+      border.0 = ui_theme.quiet_pressed_border;
+    }
+  }
+
+  pub fn press_stop(
+    event: Trigger<Pointer<Released>>,
+    mut commands: Commands,
+    mut button_colors: Query<(&mut BackgroundColor, &mut BorderColor), With<CloseButton>>,
+    ui_theme: Res<UiTheme>,
+  ) {
+    if let Ok((mut bg, mut border)) = button_colors.get_mut(event.target()) {
+      bg.0 = ui_theme.quiet_bg;
+      border.0 = ui_theme.quiet_border;
+    }
+  }
+}