Snake Game using Bevy v0.16.0

main.rs

// Original Snake Tutorial: Creating a Snake Clone in Rust, with Bevy [0.7.0]
// https://mbuffett.com/posts/bevy-snake-tutorial/

use bevy::{prelude::*, time::common_conditions::on_timer, window::PrimaryWindow};
use rand::random;
use std::time::Duration;

const SNAKE_HEAD_COLOR: Color = Color::srgb(0.7, 0.7, 0.7);
const SNAKE_SEGMENT_COLOR: Color = Color::srgb(0.3, 0.3, 0.3);
const FOOD_COLOR: Color = Color::srgb(1.0, 0.0, 1.0);

const ARENA_WIDTH: u32 = 25;
const ARENA_HEIGHT: u32 = 25;

// Resources
#[derive(Resource, Default)]
struct SnakeSegments(Vec<Entity>);

#[derive(Resource, Default)]
struct LastTailPosition(Option<Position>);

// Events
#[derive(Event)]
struct GrowthEvent;

#[derive(Event)]
struct GameOverEvent;

// Components
#[derive(Component)]
struct SnakeHead {
    direction: Direction,
}

#[derive(Component)]
struct SnakeSegment;

#[derive(Component)]
struct Food;

#[derive(Component, Clone, Copy, PartialEq, Eq)]
struct Position {
    x: i32,
    y: i32,
}

#[derive(Component)]
struct Size {
    width: f32,
    height: f32,
}

impl Size {
    pub fn square(x: f32) -> Self {
        Self {
            width: x,
            height: x,
        }
    }
}

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
enum Direction {
    Left,
    Up,
    Right,
    Down,
}

impl Direction {
    fn opposite(self) -> Self {
        match self {
            Self::Left => Self::Right,
            Self::Right => Self::Left,
            Self::Up => Self::Down,
            Self::Down => Self::Up,
        }
    }
}

fn main() {
    App::new()
        .insert_resource(ClearColor(Color::srgb(0.04, 0.04, 0.04)))
        .init_resource::<SnakeSegments>()
        .init_resource::<LastTailPosition>()
        .add_event::<GrowthEvent>()
        .add_event::<GameOverEvent>()
        .add_systems(Startup, (setup_camera, spawn_snake))
        .add_systems(Update, snake_movement_input.before(snake_movement))
        .add_systems(
            Update,
            (snake_movement, game_over, snake_eating, snake_growth)
                .chain()
                .run_if(on_timer(Duration::from_secs_f32(0.25))),
        )
        .add_systems(
            Update,
            food_spawner.run_if(on_timer(Duration::from_secs_f32(4.0))),
        )
        .add_systems(PostUpdate, (size_scaling, position_translation))
        .add_plugins(DefaultPlugins.set(WindowPlugin {
            primary_window: Some(Window {
                title: "Snake Game".into(),
                resolution: (500.0, 500.0).into(),
                ..default()
            }),
            ..default()
        }))
        .add_systems(Update, close_on_esc)
        .run();
}

fn setup_camera(mut commands: Commands) {
    commands.spawn(Camera2d);
}

fn spawn_snake(mut commands: Commands, mut segments: ResMut<SnakeSegments>) {
    *segments = SnakeSegments(vec![
        commands
            .spawn((Sprite {
                color: SNAKE_HEAD_COLOR,
                ..default()
            },))
            .insert(SnakeHead {
                direction: Direction::Up,
            })
            .insert(SnakeSegment)
            .insert(Position { x: 3, y: 3 })
            .insert(Size::square(0.8))
            .id(),
        spawn_segment(commands, Position { x: 3, y: 2 }),
    ]);
}

fn spawn_segment(mut commands: Commands, position: Position) -> Entity {
    commands
        .spawn(Sprite {
            color: SNAKE_SEGMENT_COLOR,
            ..default()
        })
        .insert(SnakeSegment)
        .insert(position)
        .insert(Size::square(0.65))
        .id()
}

fn snake_movement_input(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mut heads: Query<&mut SnakeHead>,
) {
    if let Some(mut head) = heads.iter_mut().next() {
        let dir: Direction = if keyboard_input.pressed(KeyCode::ArrowLeft) {
            Direction::Left
        } else if keyboard_input.pressed(KeyCode::ArrowDown) {
            Direction::Down
        } else if keyboard_input.pressed(KeyCode::ArrowUp) {
            Direction::Up
        } else if keyboard_input.pressed(KeyCode::ArrowRight) {
            Direction::Right
        } else {
            head.direction
        };
        if dir != head.direction.opposite() {
            head.direction = dir;
        }
    }
}

fn snake_movement(
    segments: ResMut<SnakeSegments>,
    mut heads: Query<(Entity, &SnakeHead)>,
    mut positions: Query<&mut Position>,
    mut last_tail_position: ResMut<LastTailPosition>,
    mut game_over_writer: EventWriter<GameOverEvent>,
) {
    if let Some((head_entity, head)) = heads.iter_mut().next() {
        let segment_positions = segments
            .0
            .iter()
            .map(|e| *positions.get_mut(*e).unwrap())
            .collect::<Vec<Position>>();
        let mut head_pos = positions.get_mut(head_entity).unwrap();
        match head.direction {
            Direction::Left => {
                head_pos.x -= 1;
            }
            Direction::Right => {
                head_pos.x += 1;
            }
            Direction::Up => {
                head_pos.y += 1;
            }
            Direction::Down => {
                head_pos.y -= 1;
            }
        };
        if head_pos.x < 0
            || head_pos.y < 0
            || head_pos.x as u32 >= ARENA_WIDTH
            || head_pos.y as u32 >= ARENA_HEIGHT
        {
            game_over_writer.write(GameOverEvent);
        }
        if segment_positions.contains(&head_pos) {
            game_over_writer.write(GameOverEvent);
        }
        segment_positions
            .iter()
            .zip(segments.0.iter().skip(1))
            .for_each(|(pos, segment)| {
                *positions.get_mut(*segment).unwrap() = *pos;
            });
        *last_tail_position = LastTailPosition(Some(*segment_positions.last().unwrap()));
    }
}

fn snake_eating(
    mut commands: Commands,
    mut growth_writer: EventWriter<GrowthEvent>,
    food_positions: Query<(Entity, &Position), With<Food>>,
    head_positions: Query<&Position, With<SnakeHead>>,
) {
    for head_pos in head_positions.iter() {
        for (ent, food_pos) in food_positions.iter() {
            if food_pos == head_pos {
                commands.entity(ent).despawn();
                growth_writer.write(GrowthEvent);
                break;
            }
        }
    }
}

fn snake_growth(
    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(commands, last_tail_position.0.unwrap()));
    }
}

fn food_spawner(mut commands: Commands, positions: Query<&mut Position>) {
    // Prevent food from spawning on top of snake
    let mut x = (random::<f32>() * ARENA_WIDTH as f32) as i32;
    let mut y = (random::<f32>() * ARENA_HEIGHT as f32) as i32;
    while positions.iter().any(|pos| pos.x == x && pos.y == y) {
        x = (random::<f32>() * ARENA_WIDTH as f32) as i32;
        y = (random::<f32>() * ARENA_HEIGHT as f32) as i32;
    }
    commands
        .spawn(Sprite {
            color: FOOD_COLOR,
            ..default()
        })
        .insert(Food)
        .insert(Position { x, y })
        .insert(Size::square(0.8));
}

fn size_scaling(
    primary_window: Single<&Window, With<PrimaryWindow>>,
    mut q: Query<(&Size, &mut Transform)>,
) {
    let window = primary_window;
    for (sprite_size, mut transform) in q.iter_mut() {
        transform.scale = Vec3::new(
            sprite_size.width / ARENA_WIDTH as f32 * window.width(),
            sprite_size.height / ARENA_HEIGHT as f32 * window.height(),
            1.0,
        );
    }
}

fn position_translation(
    primary_window: Single<&Window, With<PrimaryWindow>>,
    mut q: Query<(&Position, &mut Transform)>,
) {
    fn convert(pos: f32, bound_window: f32, bound_game: f32) -> f32 {
        let tile_size = bound_window / bound_game;
        pos / bound_game * bound_window - (bound_window / 2.) + (tile_size / 2.)
    }
    let window = primary_window;
    for (pos, mut transform) in q.iter_mut() {
        transform.translation = Vec3::new(
            convert(pos.x as f32, window.width(), ARENA_WIDTH as f32),
            convert(pos.y as f32, window.height(), ARENA_HEIGHT as f32),
            0.0,
        );
    }
}

fn game_over(
    mut commands: Commands,
    mut reader: EventReader<GameOverEvent>,
    segments_res: ResMut<SnakeSegments>,
    food: Query<Entity, With<Food>>,
    segments: Query<Entity, With<SnakeSegment>>,
) {
    if reader.read().next().is_some() {
        for ent in food.iter().chain(segments.iter()) {
            commands.entity(ent).despawn();
        }
        spawn_snake(commands, segments_res);
    }
}

fn close_on_esc(
    mut commands: Commands,
    focused_windows: Query<(Entity, &Window)>,
    input: Res<ButtonInput<KeyCode>>,
) {
    for (window, focus) in focused_windows.iter() {
        if !focus.focused {
            continue;
        }

        if input.just_pressed(KeyCode::Escape) {
            commands.entity(window).despawn();
        }
    }
}