Begin work on a reusable on-hover color component

The two buttons ("close" and the "Big Red" button) have identical hover
code, except for which color theme they select. I was about to start
work on the cutting board, particularly it's cut-line selectors, and
realized that would make a 3rd copy of this code.

This commit adds just the background color handler. It seems to work as
expected on the CloseButton. I'll finish removing the old observers once
I have the BorderColor version in place.

src/game/mod.rs

@@ -16,16 +16,22 @@ pub mod machines {
 
   use bevy::prelude::*;
 
+  use crate::game::consumables::Fuel;
+
   #[derive(Component)]
+  #[require(Fuel)]
   pub struct CuttingMachine;
 
   #[derive(Component)]
+  #[require(Fuel)]
   pub struct RotatingMachine;
 
   #[derive(Component)]
+  #[require(Fuel)]
   pub struct FlippingMachine;
 
   #[derive(Component)]
+  #[require(Fuel)]
   pub struct TransposingMachine;
 }
 
@@ -33,8 +39,13 @@ pub mod consumables {
   use bevy::prelude::*;
 
   #[derive(Component)]
-  pub struct Fuel(u32);
+  pub struct Fuel(pub u32);
 
+  impl Default for Fuel {
+    fn default() -> Self {
+      Self(5)
+    }
+  }
   #[derive(Event)]
   pub struct FuelChanged;
 }

src/main.rs

@@ -55,6 +55,7 @@ fn dummy_machines(mut commands: Commands) {
 
   commands
     .spawn((
+      RotatingMachine,
       Sprite::from_color(GREEN, Vec2::splat(40.0)),
       Transform::from_translation(Vec3::new(40.0, 40.0, 0.0)),
       Pickable::default(),
@@ -64,6 +65,7 @@ fn dummy_machines(mut commands: Commands) {
   // TODO: The other observers, once they have a spawner struct & impl.
   commands
     .spawn((
+      FlippingMachine,
       Sprite::from_color(PURPLE, Vec2::splat(40.)),
       Transform::from_translation(Vec3::new(-40.0, -40.0, 0.0)),
       Pickable::default(),
@@ -72,6 +74,7 @@ fn dummy_machines(mut commands: Commands) {
 
   commands
     .spawn((
+      TransposingMachine,
       Sprite::from_color(DARK_ORANGE, Vec2::splat(40.)),
       Transform::from_translation(Vec3::new(40.0, -40.0, 0.0)),
       Pickable::default(),
@@ -86,5 +89,5 @@ fn spawn_machine_ui<M: SpawnUi>(
 ) {
   let _entity = event.target;
   // TODO: Hook up the Fuel component (and spawn one so that I can)
-  M::spawn_ui(commands, theme);
+  M::spawn_ui(commands, theme, event.target());
 }

src/widgets/fuel_gauge.rs

@@ -1,9 +1,15 @@
-use bevy::{color::palettes::css::*, prelude::*, ui::Val::*};
+use bevy::{
+  color::palettes::css::*,
+  ecs::{component::HookContext, world::DeferredWorld},
+  prelude::*,
+  ui::Val::*,
+};
 
 use crate::game::consumables::{Fuel, FuelChanged};
 
 #[derive(Component)]
 #[require(Label)]
+#[component(on_add = FuelGauge::refresh_label)]
 pub struct FuelGauge(Entity);
 
 impl FuelGauge {
@@ -19,14 +25,45 @@ impl FuelGauge {
       },
       BackgroundColor(GREEN.into()),
       Text::new("Fuel: "),
-      children![TextSpan::new("<n>"),],
     )
   }
 
-  pub fn detect_fuel_change(event: Trigger<FuelChanged>) {
-    dbg!(format!(
-      "Detected fuel change on entity ID: {}",
-      event.target()
-    ));
+  /// Observer system to update the [`FuelGauge`] widget when a machine emits a
+  /// [`FuelChanged`] event.
+  pub fn detect_fuel_change(
+    event: Trigger<FuelChanged>,
+    fuel_levels: Query<&Fuel>,
+    mut gauges: Query<(&FuelGauge, &mut Text)>,
+  ) {
+    // Find the FuelGauge that references the same Entity as the event target.
+    // That gauge's `Text` is the one to update.
+    let (_, mut label) = gauges
+      .iter_mut()
+      .find(|(gauge, _label)| gauge.0 == event.target())
+      .expect("Couldn't find any fuel gauges");
+
+    let fuel = fuel_levels.get(event.target()).expect(
+      "Logic error: a `FuelChanged` event was targetted at an entity with no `Fuel` component.",
+    );
+    label.0 = format!("Fuel: {}", fuel.0);
+  }
+
+  fn refresh_label(mut world: DeferredWorld, ctx: HookContext) {
+    // Get the machine ID from the FuelGauge component.
+    let Some(machine_id) = world.get::<FuelGauge>(ctx.entity).map(|fg| fg.0) else {
+      panic!("Couldn't get a FuelGauge during it's on-add hook run!");
+    };
+    // and fuel level
+    let Some(fuel) = world.get::<Fuel>(machine_id).map(|lvl| lvl.0) else {
+      // TODO: Maybe don't panic and just emit a warning.
+      panic!("Couldn't get a Fuel for a machine during a FuelGauge on-add hook.");
+    };
+
+    // Get an excl ref to the Text component so we can redraw its text
+    let Some(mut label) = world.get_mut::<Text>(ctx.entity) else {
+      panic!()
+    };
+
+    label.0 = format!("Fuel: {}", fuel);
   }
 }

src/widgets/machines.rs

@@ -7,12 +7,12 @@ use crate::{
 };
 
 impl SpawnUi for CuttingMachine {
-  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>, machine_id: Entity) {
     let base_entity = machine_ui_base(&mut commands, "Cutting Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
       // Left panel. For fuel or machine stats or whatever.
       // TODO: Pass along target machine, not the UI's root entity.
-      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+      commands.spawn(FuelGauge::bundle(machine_id));
 
       // Center panel (placeholder for the Card view)
       commands.spawn((
@@ -37,19 +37,10 @@ impl SpawnUi for CuttingMachine {
         ))
         .with_children(|cmds| {
           let mut button_cmds = cmds.spawn(BigRedButton::bundle("CUT"));
-          button_cmds.observe(
-            |trigger: Trigger<Pointer<Click>>,
-             mut com: Commands,
-             q: Single<(Entity, &CuttingMachine)>| {
-              dbg!("Cut button pressed. Triggering a FuelChanged event");
-
-              // Feed through the target machine, once the SpawnUi trait is updated
-              // to require it gets here in the first place.
-
-              let cutting_machine = q.0;
-              com.trigger_targets(FuelChanged, cutting_machine);
-            },
-          );
+          button_cmds.observe(move |trigger: Trigger<Pointer<Click>>, mut com: Commands| {
+            dbg!("Cut button pressed. Triggering a FuelChanged event");
+            com.trigger_targets(FuelChanged, machine_id);
+          });
           // TODO: Attach on-press observer so this machine can do something
           // in response to that button being pressed
         });
@@ -58,10 +49,10 @@ impl SpawnUi for CuttingMachine {
 }
 
 impl SpawnUi for RotatingMachine {
-  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>, machine_id: Entity) {
     let base_entity = machine_ui_base(&mut commands, "Rotating Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
-      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+      commands.spawn(FuelGauge::bundle(machine_id));
 
       // Center panel (placeholder for input-output rotation)
       commands.spawn((
@@ -93,10 +84,10 @@ impl SpawnUi for RotatingMachine {
 }
 
 impl SpawnUi for FlippingMachine {
-  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>, machine_id: Entity) {
     let base_entity = machine_ui_base(&mut commands, "Flipping Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
-      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+      commands.spawn(FuelGauge::bundle(machine_id));
 
       // Center panel (placeholder)
       commands.spawn((
@@ -128,10 +119,10 @@ impl SpawnUi for FlippingMachine {
 }
 
 impl SpawnUi for TransposingMachine {
-  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>, machine_id: Entity) {
     let base_entity = machine_ui_base(&mut commands, "Transposing Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
-      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+      commands.spawn(FuelGauge::bundle(machine_id));
 
       // Center panel (placeholder)
       commands.spawn((

src/widgets/mod.rs

@@ -18,6 +18,8 @@ impl Plugin for GameUiPlugin {
     app
       .init_resource::<UiTheme>()
       .register_type::<UiTheme>()
+      .add_observer(HoverBackgroundcolor::hover_start)
+      .add_observer(HoverBackgroundcolor::hover_stop)
       .add_observer(CloseButton::hover_start)
       .add_observer(CloseButton::hover_stop)
       .add_observer(CloseButton::press_start)
@@ -30,12 +32,12 @@ impl Plugin for GameUiPlugin {
   }
 }
 
-/// Anything that can spawn a themed UI should impl this trait.
+/// Machines spawn their UI through this trait.
 ///
-/// This exists mainly so that I can write generic functions and have the *compiler*
+/// This exists mainly so that I can write generic functions and have the compiler
 /// expand the code for me, instead of doing it by hand.
 pub trait SpawnUi {
-  fn spawn_ui(commands: Commands, theme: Res<UiTheme>);
+  fn spawn_ui(commands: Commands, theme: Res<UiTheme>, machine_id: Entity);
 }
 
 /// The base panel for the machines that manipulate the room cards.
@@ -216,6 +218,7 @@ impl CloseButton {
       BackgroundColor(GRAY.into()),
       BorderColor(DARK_GRAY.into()),
       BorderRadius::all(Px(2.0)),
+      HoverBackgroundcolor::new(GREEN.into()),
       children![(
         // TODO: Replace with an icon/sprite
         Text::new("X"),
@@ -233,7 +236,7 @@ impl CloseButton {
   ) {
     // 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;
+      // bg.0 = ui_theme.quiet_hover_bg;
       border.0 = ui_theme.quiet_hover_border;
     }
   }
@@ -244,7 +247,7 @@ impl CloseButton {
     ui_theme: Res<UiTheme>,
   ) {
     if let Ok((mut bg, mut border)) = button_colors.get_mut(event.target()) {
-      bg.0 = ui_theme.quiet_bg;
+      // bg.0 = ui_theme.quiet_bg;
       border.0 = ui_theme.quiet_border;
     }
   }
@@ -273,3 +276,48 @@ impl CloseButton {
     }
   }
 }
+
+/// Background color to use for an item being hovered over.
+///
+/// Adding this to an entity both sets the color and implicitly enables the
+/// on-hover behavior. Without it, the system(s) don't find the entity and so
+/// no color changing is exhibited.
+#[derive(Component)]
+struct HoverBackgroundcolor {
+  pub color: Color,
+  // hold onto the original so it can be put back
+  orig_bg: Option<Color>,
+}
+
+impl HoverBackgroundcolor {
+  fn new(color: Color) -> Self {
+    Self {
+      color,
+      orig_bg: None,
+    }
+  }
+
+  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 colors: Query<(&mut HoverBackgroundcolor, &mut BackgroundColor)>,
+  ) {
+    // Get the components for only the Trigger's target entity
+    if let Ok((mut hover, mut bg)) = colors.get_mut(event.target()) {
+      hover.orig_bg = Some(bg.0); // store the original
+      bg.0 = hover.color;
+    }
+  }
+
+  fn hover_stop(
+    event: Trigger<Pointer<Out>>,
+    mut colors: Query<(&HoverBackgroundcolor, &mut BackgroundColor)>,
+  ) {
+    if let Ok((hover, mut bg)) = colors.get_mut(event.target()) {
+      bg.0 = hover
+        .orig_bg
+        .expect("Tried to restore an original color but there was none!");
+    }
+  }
+}