games/src/bin/flappy/main.rs

use bevy::{input::common_conditions::input_just_released, render::view::VisibleEntities};
use games::*;

fn main() {
    App::new()
        .add_plugins(BaseGamePlugin {
            name: "flappy bird (with rewind)".into(),
        })
        .init_state::<PlayerState>()
        .add_systems(Startup, (init_bird, init_ground, init_ui, tweak_camera.after(setup_camera)))
        .add_systems(OnEnter(PlayerState::Alive), alive_bird)
        .add_systems(OnExit(PlayerState::Alive), kill_bird)
        .add_systems(
            Update,
            (
                // Systems to run when player state changes
                (
                    // Print out when this state changes for debugging purposes
                    debug_state_changes::<PlayerState>,
                    // Toggle (UI) elements when the player dies/alives
                    toggle_state_visibility::<PlayerState>,
                ).run_if(state_changed::<PlayerState>),
                // Detect if the bird is "dead" by checking if it is visible
                // from the point of view of the camera
                detect_dead.run_if(in_state(PlayerState::Alive)),
                // Toggle rewinding state when "R" is pressed/released
                toggle_rewind.run_if(
                    input_just_pressed(KeyCode::KeyR).or(input_just_released(KeyCode::KeyR)),
                ),
                // Systems to run in the "play" state
                (
                    // Only flap when we press the space key
                    flap.run_if(input_just_pressed(KeyCode::Space)),
                    // Rewinding systems
                    record.run_if(any_component_changed::<Transform>),
                )
                    .run_if(in_state(PlayerState::Alive)),
                // Rewinding systems
                rewind.run_if(in_state(PlayerState::Rewind)),
            ),
        )
        .run();
}

fn tweak_camera(
    mut camera: Query<(&mut Camera, &mut AmbientLight), With<Camera>>,
) {
    camera.iter_mut().for_each(|(mut c, mut al)| {
        c.clear_color = ClearColorConfig::Custom(WHITE.into());
        al.brightness = 100.0;
    });
}

#[derive(Component)]
struct Bird;

#[derive(States, Clone, Eq, PartialEq, Debug, Hash, Default, Component)]
enum PlayerState {
    #[default]
    Alive,
    Rewind,
    Dead,
}

// A tape tracking the bird's state every frame
#[derive(Component, Default)]
struct Tape {
    translations: Vec<Vec3>,
    rotations: Vec<Quat>,
}

fn init_bird(
    mut commands: Commands,
    server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let material = MeshMaterial3d(materials.add(StandardMaterial {
        base_color_texture: Some(server.load("flappy/bevy.png")),
        base_color: WHITE.into(),
        alpha_mode: AlphaMode::Blend,
        ..default()
    }));

    let mesh = Mesh3d(meshes.add(Plane3d::new(Vec3::Y, Vec2::splat(1.0))));

    let name = Name::new("bird");

    let t = Transform::from_xyz(0.0, 0.0, -10.0).with_rotation(Quat::from_rotation_x(PI / 2.0));

    let physics = (
        RigidBody::Dynamic,
        Collider::capsule(1.0, 1.0), Mass(1.0),
        ExternalForce::new(Vec3::X * 1.0).with_persistence(true),
        ExternalImpulse::default().with_persistence(false),
        LockedAxes::ROTATION_LOCKED.lock_translation_z(),
    );

    let tape = Tape::default();

    commands.spawn((name, mesh, material, physics, t, Bird, tape));
}

#[derive(Component)]
struct Ground;

fn init_ground(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let material = MeshMaterial3d(materials.add(StandardMaterial {
        base_color: GREEN.into(),
        ..default()
    }));

    let mesh = Mesh3d(meshes.add(Cuboid::new(10.0, 1.0, 1.0)));

    let name = Name::new("ground");

    let t = Transform::from_xyz(0.0, -4.0, -10.0);

    let physics = (RigidBody::Static, Collider::cuboid(1.0, 1.0, 1.0));

    commands.spawn((name, mesh, material, physics, t, Ground));
}

fn init_ui(
    mut commands: Commands,
) {
    commands.spawn((
        Node {
            align_self: AlignSelf::Center,
            justify_self: JustifySelf::Center,
            flex_direction: FlexDirection::Column,
            ..default()
        },
        PlayerState::Dead,
        children![
            Text::new("You Died"),
            Text::new("Press R to Rewind"),
        ],
    ));
}

// TODO: Create floor (and ceiling?)
// Q: Move bird + camera or move world around bird & camera?
// TODO: Obstacles

fn flap(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    #[cfg(debug_assertions)] keycode: Res<ButtonInput<KeyCode>>,
    mut bird: Query<(&Transform, &mut ExternalImpulse), With<Bird>>,
) {
    debug_assert!(
        matches!(state.get(), PlayerState::Alive),
        "Only flap when playing"
    );
    debug_assert!(
        keycode.just_pressed(KeyCode::Space),
        "Only flap when space is just pressed"
    );

    bird.iter_mut().for_each(|(t, mut f)| {
        f.apply_impulse(t.rotation * Vec3::NEG_Z * 5.0);
    });
}

fn toggle_rewind(keycode: Res<ButtonInput<KeyCode>>, mut next: ResMut<NextState<PlayerState>>) {
    debug_assert!(
        keycode.just_pressed(KeyCode::KeyR) || keycode.just_released(KeyCode::KeyR),
        "Only toggle rewind when R is pressed"
    );

    if keycode.just_pressed(KeyCode::KeyR) {
        debug!("Toggling rewind ON");
        next.set(PlayerState::Rewind)
    } else {
        debug!("Toggling rewind OFF");
        next.set(PlayerState::Alive)
    }
}

fn record(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    mut birds: Query<(&Transform, &mut Tape), With<Bird>>,
) {
    debug_assert!(
        matches!(state.get(), PlayerState::Alive),
        "Only record in the alive state"
    );

    birds.iter_mut().for_each(|(transform, mut tape)| {
        tape.translations.push(transform.translation);
        tape.rotations.push(transform.rotation);
    });
}

fn rewind(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    mut birds: Query<(&mut Transform, &mut Tape), With<Bird>>,
) {
    debug_assert!(
        matches!(state.get(), PlayerState::Rewind),
        "Only rewind in the rewinding state"
    );

    birds.iter_mut().for_each(|(mut transform, mut tape)| {
        if let Some(t) = tape.translations.pop() {
            transform.translation = t;
        }
        if let Some(r) = tape.rotations.pop() {
            transform.rotation = r;
        }
    });
}

// PERF: Runs more than it needs, should only execute when bird enters/exit frame
fn detect_dead(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    bird: Single<&ColliderAabb, With<Bird>>,
    ground: Single<&ColliderAabb, With<Ground>>,
    mut next: ResMut<NextState<PlayerState>>,
) {
    debug_assert!(
        matches!(state.get(), PlayerState::Alive),
        "Only check if dead while alive"
    );
    if bird.intersects(*ground) {
        next.set(PlayerState::Dead);
    }
}

fn alive_bird(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    mut bird: Single<&mut RigidBody, With<Bird>>,
) {
    debug_assert!(!matches!(state.get(), PlayerState::Dead));
    debug!("Aliving bird");
    **bird = RigidBody::Dynamic;
}

fn kill_bird(
    #[cfg(debug_assertions)] state: Res<State<PlayerState>>,
    mut bird: Single<&mut RigidBody, With<Bird>>,
) {
    debug_assert!(!matches!(state.get(), PlayerState::Alive));
    debug!("Killing bird");
    **bird = RigidBody::Static;
}