steam-train/src/main.rs

use bevy::{
    prelude::*,
    render::{camera::Camera, render_graph::base::camera::CAMERA_2D},
};

#[derive(Default, Debug)]
struct Player {
    entity: Option<Entity>,
    x: isize,
    y: isize,
}

#[derive(Default)]
struct GameState {
    player: Player,
    score: u32,
    camera_focus: Vec3,
}

fn main() {
    App::build()
        .init_resource::<GameState>()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(movement.system())
        .add_system(focus_camera.system())
        .run();
}

fn setup(
    mut commands: Commands,
    mut state: ResMut<GameState>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    state.score = 0;
    // assuming that bounds are (900, 600)
    state.player.x = 0;
    state.player.y = -50;

    // cameras
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
    commands.spawn_bundle(UiCameraBundle::default());

    // create the player
    state.player.entity = Some(
        commands
            .spawn_bundle(SpriteBundle {
                material: materials.add(Color::GOLD.into()),
                transform: Transform::from_xyz(0.0, -50.0, 1.0),
                sprite: Sprite::new(Vec2::new(30.0, 30.0)),
                ..Default::default()
            })
            .id(),
    );

    // Add walls!
    let wall_thickness = 10.0;
    let bounds = Vec2::new(900.0, 600.0);

    // left
    commands.spawn_bundle(SpriteBundle {
        transform: Transform::from_xyz(-bounds.x / 2.0, 0.0, 0.0),
        sprite: Sprite::new(Vec2::new(wall_thickness, bounds.y + wall_thickness)),
        ..Default::default()
    });
    // right
    commands.spawn_bundle(SpriteBundle {
        transform: Transform::from_xyz(bounds.x / 2.0, 0.0, 0.0),
        sprite: Sprite::new(Vec2::new(wall_thickness, bounds.y + wall_thickness)),
        ..Default::default()
    });
    // bottom
    commands.spawn_bundle(SpriteBundle {
        transform: Transform::from_xyz(0.0, -bounds.y / 2.0, 0.0),
        sprite: Sprite::new(Vec2::new(bounds.x + wall_thickness, wall_thickness)),
        ..Default::default()
    });
    commands.spawn_bundle(SpriteBundle {
        transform: Transform::from_xyz(0.0, bounds.y / 2.0, 0.0),
        sprite: Sprite::new(Vec2::new(bounds.x + wall_thickness, wall_thickness)),
        ..Default::default()
    });
}

fn movement(
    keyboard_input: Res<Input<KeyCode>>,
    mut query: Query<&mut Transform>,
    mut game: ResMut<GameState>,
) {
    let mut moved = false;
    if keyboard_input.pressed(KeyCode::Left) {
        game.player.x -= 5;
        moved = true;
    }
    if keyboard_input.pressed(KeyCode::Right) {
        game.player.x += 5;
        moved = true;
    }
    if keyboard_input.pressed(KeyCode::Up) {
        game.player.y += 5;
        moved = true;
    }
    if keyboard_input.pressed(KeyCode::Down) {
        game.player.y -= 5;
        moved = true;
    }

    // limit movement of player
    game.player.x = game.player.x.min(435).max(-435);
    game.player.y = game.player.y.min(285).max(-285);

    if moved {
        if let Some(entity) = game.player.entity {
            *query.get_mut(entity).unwrap() = Transform {
                translation: Vec3::new(game.player.x as f32, game.player.y as f32, 0.0),
                ..Default::default()
            };
        }
    }
}

fn focus_camera(
    mut game: ResMut<GameState>,
    mut transforms: QuerySet<(Query<(&mut Transform, &Camera)>, Query<&Transform>)>,
) {
    if let Some(player_entity) = game.player.entity {
        if let Ok(player_transform) = transforms.q1().get(player_entity) {
            game.camera_focus = player_transform.translation;
        }
    }

    for (mut transform, camera) in transforms.q0_mut().iter_mut() {
        if camera.name == Some(CAMERA_2D.to_string()) {
            *transform.translation = *game.camera_focus;
        }
    }
}