working tail

src/game/main.rs

@@ -32,10 +32,6 @@ fn change_names(mut query: Query<&mut Name, With<Person>>) {
     }
 }
 
-fn hello_world() {
-    println!("hello world!");
-}
-
 pub struct HelloPlugin;
 
 impl Plugin for HelloPlugin {

src/snake/main.rs

@@ -1,9 +1,14 @@
-use bevy::{prelude::*, window::PrimaryWindow};
-use bevy_inspector_egui::quick::WorldInspectorPlugin;
+use std::time::Duration;
 
-const SNAKE_HEAD_COLOR: Color = Color::srgb(0.7, 1.0, 0.7);
-const ARENA_WIDTH: u32 = 20;
-const ARENA_HEIGHT: u32 = 15;
+use bevy::{prelude::*, time::common_conditions::on_timer, window::PrimaryWindow};
+use bevy_inspector_egui::quick::WorldInspectorPlugin;
+use rand::prelude::random;
+
+const SNAKE_HEAD_COLOR: Color = Color::srgb(0.5, 0.7, 0.5);
+const SNAKE_SEGMENT_COLOR: Color = Color::srgb(0.3, 0.5, 0.3);
+const FOOD_COLOR: Color = Color::srgb(0.7, 0.5, 0.7);
+const ARENA_WIDTH: u32 = 15;
+const ARENA_HEIGHT: u32 = 10;
 const WINDOW_WIDTH: f32 = 1280.0;
 
 #[derive(Eq, PartialEq, Copy, Clone)]
@@ -31,6 +36,18 @@ struct SnakeHead {
 }
 
 #[derive(Component)]
+struct SnakeSegment;
+
+#[derive(Resource, Default)]
+struct SnakeSegments(Vec<Entity>);
+
+#[derive(Resource, Default)]
+struct LastTailPosition(Option<Position>);
+
+#[derive(Component)]
+struct Food;
+
+#[derive(Component, Clone, Copy, Eq, PartialEq)]
 struct Position {
     x: i32,
     y: i32,
@@ -51,10 +68,7 @@ impl Size {
     }
 }
 
-#[derive(Resource)]
-struct MovementTimer(Timer);
-
-fn snake_movement_input(input: Res<ButtonInput<KeyCode>>, mut heads: Query<(&mut SnakeHead)>) {
+fn snake_movement_input(input: Res<ButtonInput<KeyCode>>, mut heads: Query<&mut SnakeHead>) {
     if let Some(mut head) = heads.iter_mut().next() {
         let dir: Direction = if input.pressed(KeyCode::ArrowUp) {
             Direction::Up
@@ -75,24 +89,33 @@ fn snake_movement_input(input: Res<ButtonInput<KeyCode>>, mut heads: Query<(&mut
 }
 
 fn snake_movement(
-    input: Res<ButtonInput<KeyCode>>,
-    time: Res<Time>,
-    mut timer: ResMut<MovementTimer>,
-    mut heads: Query<(&SnakeHead, &mut Position)>,
+    segments: Res<SnakeSegments>,
+    heads: Query<(Entity, &SnakeHead)>,
+    mut positions: Query<&mut Position>,
+    mut last_tail_position: ResMut<LastTailPosition>,
 ) {
-    if let Some((head, mut pos)) = heads.iter_mut().next() {
-        if timer.0.tick(time.delta()).just_finished() {
-            if head.direction == Direction::Up {
-                pos.y += 1;
-            } else if head.direction == Direction::Down {
-                pos.y -= 1;
-            } else if head.direction == Direction::Left {
-                pos.x -= 1;
-            } else if head.direction == Direction::Right {
-                pos.x += 1;
-            }
-        }
+    // Filter positions to just the segments
+    let segment_positions = segments
+        .0
+        .iter()
+        .map(|entity| *positions.get_mut(*entity).unwrap())
+        .collect::<Vec<Position>>();
+    let (head_entity, head) = heads.single();
+    let mut head_pos = positions.get_mut(head_entity).unwrap();
+
+    match &head.direction {
+        Direction::Up => head_pos.y += 1,
+        Direction::Down => head_pos.y -= 1,
+        Direction::Left => head_pos.x -= 1,
+        Direction::Right => head_pos.x += 1,
     }
+    segment_positions
+        .iter()
+        .zip(segments.0.iter().skip(1))
+        .for_each(|(pos, segment)| {
+            *positions.get_mut(*segment).unwrap() = *pos;
+        });
+    last_tail_position.0 = Some(*segment_positions.last().unwrap());
 }
 
 fn scale_translation(
@@ -131,18 +154,81 @@ fn position_translation(
     }
 }
 
-fn setup_player(mut commands: Commands) {
+fn spawn_segment(commands: &mut Commands, pos: Position) -> Entity {
+    commands
+        .spawn(Sprite {
+            color: SNAKE_SEGMENT_COLOR,
+            ..Default::default()
+        })
+        .insert(SnakeSegment)
+        .insert(Name::new(String::from("SnakeSegment")))
+        .insert(pos)
+        .insert(Size::square(0.77))
+        .id()
+}
+
+fn spawn_food(mut commands: Commands) {
+    commands
+        .spawn(Sprite {
+            color: FOOD_COLOR,
+            ..default()
+        })
+        .insert(Position {
+            x: (random::<f32>() * ARENA_WIDTH as f32) as i32,
+            y: (random::<f32>() * ARENA_HEIGHT as f32) as i32,
+        })
+        .insert(Name::new(String::from("Food")))
+        .insert(Size::square(0.8))
+        .insert(Food);
+}
+
+fn spawn_snake(mut commands: Commands, mut segments: ResMut<SnakeSegments>) {
+    *segments = SnakeSegments(vec![
         commands
             .spawn(Sprite {
                 color: SNAKE_HEAD_COLOR,
-            custom_size: Some(Vec2::new(1.0, 1.0)),
                 ..default()
             })
             .insert(SnakeHead {
                 direction: Direction::Right,
             })
-        .insert(Position { x: 0, y: 0 })
-        .insert(Size::square(1.0));
+            .insert(Size::square(1.0))
+            .insert(Name::new(String::from("Snake Head")))
+            .insert(Position { x: 5, y: 0 })
+            .id(),
+        spawn_segment(&mut commands, Position { x: 4, y: 0 }),
+    ])
+}
+
+#[derive(Event)]
+struct GrowthEvent;
+
+fn snake_eating(
+    mut commands: Commands,
+    mut growth_writer: EventWriter<GrowthEvent>,
+    food_positions: Query<(Entity, &Position), With<Food>>,
+    head_positions: Query<&Position, With<SnakeHead>>,
+) {
+    let head_pos = head_positions.single();
+    for (ent, food_pos) in food_positions.iter() {
+        if food_pos == head_pos {
+            commands.entity(ent).despawn();
+            growth_writer.send(GrowthEvent);
+        }
+    }
+}
+
+fn snake_growth(
+    mut commands: Commands,
+    last_tail_position: Res<LastTailPosition>,
+    mut segments: ResMut<SnakeSegments>,
+    mut growth_reader: EventReader<GrowthEvent>,
+) {
+    if growth_reader.read().next().is_some() {
+        segments
+            .0
+            .push(spawn_segment(&mut commands, last_tail_position.0.unwrap()));
+    }
 }
 
 fn setup_camera(mut commands: Commands) {
@@ -152,15 +238,28 @@ fn setup_camera(mut commands: Commands) {
 pub struct SnakePlugin;
 impl Plugin for SnakePlugin {
     fn build(&self, app: &mut App) {
-        app.add_systems(Startup, (setup_camera, setup_player));
-        app.add_systems(Update, snake_movement_input);
-        app.add_systems(FixedUpdate, snake_movement);
-        app.add_systems(PostUpdate, (scale_translation, position_translation));
+        app.add_systems(Startup, (setup_camera, spawn_snake))
+            .add_systems(
+                Update,
+                (
+                    snake_movement_input,
+                    (spawn_food).run_if(on_timer(Duration::from_secs(3))),
+                ),
+            )
+            .add_systems(
+                FixedUpdate,
+                (snake_movement, snake_eating, snake_growth)
+                    .chain()
+                    .run_if(on_timer(Duration::from_millis(500))),
+            )
+            .add_systems(PostUpdate, (scale_translation, position_translation));
 
-        app.insert_resource(MovementTimer(Timer::from_seconds(
-            1.0,
-            TimerMode::Repeating,
-        )));
+        app.insert_resource(SnakeSegments::default())
+            .insert_resource(LastTailPosition::default());
+
+        // Events must be added to the app before they can be used
+        // using the 'add_event' method
+        app.add_event::<GrowthEvent>();
     }
 }