Add OnPress callbacks

src/screens/credits.rs

@@ -11,21 +11,11 @@ use crate::{
 pub(super) fn plugin(app: &mut App) {
     app.add_systems(OnEnter(Screen::Credits), show_credits_screen);
     app.add_systems(OnExit(Screen::Credits), disable_soundtrack);
-
-    app.add_systems(
-        Update,
-        handle_credits_action.run_if(in_state(Screen::Credits)),
-    );
-    app.register_type::<CreditsAction>();
-}
-
-#[derive(Component, Debug, Clone, Copy, PartialEq, Eq, Reflect)]
-#[reflect(Component)]
-enum CreditsAction {
-    Back,
 }
 
 fn show_credits_screen(mut commands: Commands) {
+    let enter_title = commands.register_one_shot_system(enter_title);
+
     commands
         .ui_root()
         .insert(StateScoped(Screen::Credits))
@@ -39,7 +29,7 @@ fn show_credits_screen(mut commands: Commands) {
             children.label("Ducky sprite - CC0 by Caz Creates Games");
             children.label("Music - CC BY 3.0 by Kevin MacLeod");
 
-            children.button("Back").insert(CreditsAction::Back);
+            children.button("Back").insert(OnPress(enter_title));
         });
 
     commands.trigger(PlaySoundtrack::Key(SoundtrackKey::Credits));
@@ -49,15 +39,6 @@ fn disable_soundtrack(mut commands: Commands) {
     commands.trigger(PlaySoundtrack::Disable);
 }
 
-fn handle_credits_action(
-    mut next_screen: ResMut<NextState<Screen>>,
-    mut button_query: Query<(&Interaction, &CreditsAction), Changed<Interaction>>,
-) {
-    for (interaction, action) in &mut button_query {
-        if matches!(interaction, Interaction::Pressed) {
-            match action {
-                CreditsAction::Back => next_screen.set(Screen::Title),
-            }
-        }
-    }
+fn enter_title(mut next_screen: ResMut<NextState<Screen>>) {
+    next_screen.set(Screen::Title);
 }

src/screens/title.rs

@@ -7,50 +7,35 @@ use crate::ui::prelude::*;
 
 pub(super) fn plugin(app: &mut App) {
     app.add_systems(OnEnter(Screen::Title), show_title_screen);
-
-    app.register_type::<TitleAction>();
-    app.add_systems(Update, handle_title_action.run_if(in_state(Screen::Title)));
 }
 
-#[derive(Component, Debug, Clone, Copy, PartialEq, Eq, Reflect)]
-#[reflect(Component)]
-enum TitleAction {
-    Play,
-    Credits,
-    /// Exit doesn't work well with embedded applications.
+fn show_title_screen(mut commands: Commands) {
+    let enter_playing = commands.register_one_shot_system(enter_playing);
+    let enter_credits = commands.register_one_shot_system(enter_credits);
     #[cfg(not(target_family = "wasm"))]
-    Exit,
-}
+    let exit_app = commands.register_one_shot_system(exit_app);
 
-fn show_title_screen(mut commands: Commands) {
     commands
         .ui_root()
         .insert(StateScoped(Screen::Title))
         .with_children(|children| {
-            children.button("Play").insert(TitleAction::Play);
-            children.button("Credits").insert(TitleAction::Credits);
+            children.button("Play").insert(OnPress(enter_playing));
+            children.button("Credits").insert(OnPress(enter_credits));
 
             #[cfg(not(target_family = "wasm"))]
-            children.button("Exit").insert(TitleAction::Exit);
+            children.button("Exit").insert(OnPress(exit_app));
         });
 }
 
-fn handle_title_action(
-    mut next_screen: ResMut<NextState<Screen>>,
-    mut button_query: Query<(&Interaction, &TitleAction), Changed<Interaction>>,
-    #[cfg(not(target_family = "wasm"))] mut app_exit: EventWriter<AppExit>,
-) {
-    for (interaction, action) in &mut button_query {
-        if matches!(interaction, Interaction::Pressed) {
-            match action {
-                TitleAction::Play => next_screen.set(Screen::Playing),
-                TitleAction::Credits => next_screen.set(Screen::Credits),
-
-                #[cfg(not(target_family = "wasm"))]
-                TitleAction::Exit => {
-                    app_exit.send(AppExit::Success);
-                }
-            }
-        }
-    }
+fn enter_playing(mut next_screen: ResMut<NextState<Screen>>) {
+    next_screen.set(Screen::Playing);
+}
+
+fn enter_credits(mut next_screen: ResMut<NextState<Screen>>) {
+    next_screen.set(Screen::Credits);
+}
+
+#[cfg(not(target_family = "wasm"))]
+fn exit_app(mut app_exit: EventWriter<AppExit>) {
+    app_exit.send(AppExit::Success);
 }

src/ui/interaction.rs

@@ -1,10 +1,18 @@
-use bevy::prelude::*;
+use bevy::{ecs::system::SystemId, prelude::*};
 
 use crate::game::{assets::SfxKey, audio::sfx::PlaySfx};
 
 pub(super) fn plugin(app: &mut App) {
     app.register_type::<InteractionPalette>();
-    app.add_systems(Update, (apply_interaction_palette, trigger_interaction_sfx));
+    app.register_type::<OnPress>();
+    app.add_systems(
+        Update,
+        (
+            apply_on_press,
+            apply_interaction_palette,
+            trigger_interaction_sfx,
+        ),
+    );
 }
 
 /// Palette for widget interactions. Add this to an entity that supports [`Interaction`]s, such as a button,
@@ -17,6 +25,24 @@ pub struct InteractionPalette {
     pub pressed: Color,
 }
 
+/// Component that calls a [one-shot system](https://bevyengine.org/news/bevy-0-12/#one-shot-systems)
+/// when the [`Interaction`] component on the same entity changes to [`Interaction::Pressed`].
+/// Use this in conjuction with [`Commands::register_one_shot_system`] to create a callback for e.g. a button press.
+#[derive(Component, Debug, Reflect, Deref, DerefMut)]
+#[reflect(Component, from_reflect = false)]
+pub struct OnPress(#[reflect(ignore)] pub SystemId);
+
+fn apply_on_press(
+    interactions: Query<(&Interaction, &OnPress), Changed<Interaction>>,
+    mut commands: Commands,
+) {
+    for (interaction, &OnPress(system_id)) in &interactions {
+        if matches!(interaction, Interaction::Pressed) {
+            commands.run_system(system_id);
+        }
+    }
+}
+
 fn apply_interaction_palette(
     mut palette_query: Query<
         (&Interaction, &InteractionPalette, &mut BackgroundColor),
@@ -34,10 +60,10 @@ fn apply_interaction_palette(
 }
 
 fn trigger_interaction_sfx(
-    mut interactions: Query<&Interaction, Changed<Interaction>>,
+    interactions: Query<&Interaction, Changed<Interaction>>,
     mut commands: Commands,
 ) {
-    for interaction in &mut interactions {
+    for interaction in &interactions {
         match interaction {
             Interaction::Hovered => commands.trigger(PlaySfx::Key(SfxKey::ButtonHover)),
             Interaction::Pressed => commands.trigger(PlaySfx::Key(SfxKey::ButtonPress)),

src/ui/mod.rs

@@ -9,7 +9,7 @@ mod widgets;
 
 pub mod prelude {
     pub use super::{
-        interaction::InteractionPalette,
+        interaction::{InteractionPalette, OnPress},
         palette as ui_palette,
         widgets::{Containers as _, Widgets as _},
     };