bevy-snake-tutorial/src/main.rs

use bevy::prelude::*;
use bevy::render::pass::ClearColor;
use rand::prelude::random;
use std::time::Duration;

const ARENA_WIDTH: u32 = 10;
const ARENA_HEIGHT: u32 = 10;

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

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

struct SnakeHead {
    direction: Direction,
}
struct Materials {
    head_material: Handle<ColorMaterial>,
    segment_material: Handle<ColorMaterial>,
    food_material: Handle<ColorMaterial>,
}

struct SnakeMoveTimer(Timer);

struct SnakeSegment;

#[derive(Default)]
struct SnakeSegments(Vec<Entity>);

struct Food;

struct FoodSpawnTimer(Timer);
impl Default for FoodSpawnTimer {
    fn default() -> Self {
        Self(Timer::new(Duration::from_millis(1000), true))
    }
}

#[derive(PartialEq, Copy, Clone)]
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 setup(commands: &mut Commands, mut materials: ResMut<Assets<ColorMaterial>>) {
    commands.spawn(Camera2dBundle::default());
    commands.insert_resource(Materials {
        head_material: materials.add(Color::rgb(0.7, 0.7, 0.7).into()),
        segment_material: materials.add(Color::rgb(0.3, 0.3, 0.3).into()),
        food_material: materials.add(Color::rgb(1.0, 0.0, 1.0).into()),
    });
}

fn spawn_snake(
    commands: &mut Commands,
    materials: Res<Materials>,
    mut segments: ResMut<SnakeSegments>,
) {
    segments.0 = vec![
        commands
            .spawn(SpriteBundle {
                material: materials.head_material.clone(),
                sprite: Sprite::new(Vec2::new(10.0, 10.0)),
                ..Default::default()
            })
            .with(SnakeHead {
                direction: Direction::Up,
            })
            .with(SnakeSegment)
            .with(Position { x: 3, y: 3 })
            .with(Size::square(0.8))
            .current_entity()
            .unwrap(),
        spawn_segment(
            commands,
            &materials.segment_material,
            Position { x: 3, y: 2 },
        ),
    ];
}

fn spawn_segment(
    commands: &mut Commands,
    material: &Handle<ColorMaterial>,
    position: Position,
) -> Entity {
    commands
        .spawn(SpriteBundle {
            material: material.clone(),
            ..Default::default()
        })
        .with(SnakeSegment)
        .with(position)
        .with(Size::square(0.65))
        .current_entity()
        .unwrap()
}

fn snake_movement(
    keyboard_input: Res<Input<KeyCode>>,
    snake_timer: ResMut<SnakeMoveTimer>,
    mut heads: Query<(Entity, &mut SnakeHead)>,
    mut positions: Query<&mut Position>,
) {
    if let Some((head_entity, mut head)) = heads.iter_mut().next() {
        let mut head_pos = positions.get_mut(head_entity).unwrap();
        let dir: Direction = if keyboard_input.pressed(KeyCode::Left) {
            Direction::Left
        } else if keyboard_input.pressed(KeyCode::Down) {
            Direction::Down
        } else if keyboard_input.pressed(KeyCode::Up) {
            Direction::Up
        } else if keyboard_input.pressed(KeyCode::Right) {
            Direction::Right
        } else {
            head.direction
        };
        if dir != head.direction.opposite() {
            head.direction = dir;
        }
        if !snake_timer.0.finished() {
            return;
        }
        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;
            }
        };
    }
}

fn size_scaling(windows: Res<Windows>, mut q: Query<(&Size, &mut Sprite)>) {
    let window = windows.get_primary().unwrap();
    for (sprite_size, mut sprite) in q.iter_mut() {
        sprite.size = Vec2::new(
            sprite_size.width / ARENA_WIDTH as f32 * window.width() as f32,
            sprite_size.height / ARENA_HEIGHT as f32 * window.height() as f32,
        );
    }
}

fn position_translation(windows: Res<Windows>, 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 = windows.get_primary().unwrap();
    for (pos, mut transform) in q.iter_mut() {
        transform.translation = Vec3::new(
            convert(pos.x as f32, window.width() as f32, ARENA_WIDTH as f32),
            convert(pos.y as f32, window.height() as f32, ARENA_HEIGHT as f32),
            0.0,
        );
    }
}

fn food_spawner(
    commands: &mut Commands,
    materials: Res<Materials>,
    time: Res<Time>,
    mut timer: Local<FoodSpawnTimer>,
) {
    if timer.0.tick(time.delta_seconds()).finished() {
        commands
            .spawn(SpriteBundle {
                material: materials.food_material.clone(),
                ..Default::default()
            })
            .with(Food)
            .with(Position {
                x: (random::<f32>() * ARENA_WIDTH as f32) as i32,
                y: (random::<f32>() * ARENA_HEIGHT as f32) as i32,
            })
            .with(Size::square(0.8));
    }
}

fn snake_timer(time: Res<Time>, mut snake_timer: ResMut<SnakeMoveTimer>) {
    snake_timer.0.tick(time.delta_seconds());
}

fn main() {
    App::build()
        .add_resource(ClearColor(Color::rgb(0.04, 0.04, 0.04)))
        .add_resource(WindowDescriptor {
            title: "Snake!".to_string(),
            width: 500.0,
            height: 500.0,
            ..Default::default()
        })
        .add_resource(SnakeMoveTimer(Timer::new(Duration::from_millis(150), true)))
        .add_resource(SnakeSegments::default())
        .add_startup_system(setup.system())
        .add_startup_stage("game_setup", SystemStage::single(spawn_snake.system()))
        .add_system(snake_movement.system())
        .add_system(position_translation.system())
        .add_system(size_scaling.system())
        .add_system(food_spawner.system())
        .add_system(snake_timer.system())
        .add_plugins(DefaultPlugins)
        .run();
}