Support Warning

WebGPU is currently only supported on Chrome starting with version 113, and only on desktop. If they don't work on your configuration, you can check the WebGL2 examples here.

//! This example displays each contributor to the bevy source code as a bouncing bevy-ball.

use bevy::{
    prelude::*,
    utils::{thiserror, HashSet},
};
use rand::{prelude::SliceRandom, Rng};
use std::{
    env::VarError,
    io::{self, BufRead, BufReader},
    process::Stdio,
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .init_resource::<SelectionState>()
        .add_systems(Startup, (setup_contributor_selection, setup))
        .add_systems(
            Update,
            (
                velocity_system,
                move_system,
                collision_system,
                select_system,
            ),
        )
        .run();
}

// Store contributors in a collection that preserves the uniqueness
type Contributors = HashSet<String>;

#[derive(Resource)]
struct ContributorSelection {
    order: Vec<Entity>,
    idx: usize,
}

#[derive(Resource)]
struct SelectionState {
    timer: Timer,
    has_triggered: bool,
}

impl Default for SelectionState {
    fn default() -> Self {
        Self {
            timer: Timer::from_seconds(SHOWCASE_TIMER_SECS, TimerMode::Repeating),
            has_triggered: false,
        }
    }
}

#[derive(Component)]
struct ContributorDisplay;

#[derive(Component)]
struct Contributor {
    name: String,
    hue: f32,
}

#[derive(Component)]
struct Velocity {
    translation: Vec3,
    rotation: f32,
}

const GRAVITY: f32 = 9.821 * 100.0;
const SPRITE_SIZE: f32 = 75.0;

const SATURATION_DESELECTED: f32 = 0.3;
const LIGHTNESS_DESELECTED: f32 = 0.2;
const SATURATION_SELECTED: f32 = 0.9;
const LIGHTNESS_SELECTED: f32 = 0.7;
const ALPHA: f32 = 0.92;

const SHOWCASE_TIMER_SECS: f32 = 3.0;

const CONTRIBUTORS_LIST: &[&str] = &["Carter Anderson", "And Many More"];

fn setup_contributor_selection(mut commands: Commands, asset_server: Res<AssetServer>) {
    // Load contributors from the git history log or use default values from
    // the constant array. Contributors must be unique, so they are stored in a HashSet
    let contribs = contributors().unwrap_or_else(|_| {
        CONTRIBUTORS_LIST
            .iter()
            .map(|name| name.to_string())
            .collect()
    });

    let texture_handle = asset_server.load("branding/icon.png");

    let mut contributor_selection = ContributorSelection {
        order: Vec::with_capacity(contribs.len()),
        idx: 0,
    };

    let mut rng = rand::thread_rng();

    for name in contribs {
        let pos = (rng.gen_range(-400.0..400.0), rng.gen_range(0.0..400.0));
        let dir = rng.gen_range(-1.0..1.0);
        let velocity = Vec3::new(dir * 500.0, 0.0, 0.0);
        let hue = rng.gen_range(0.0..=360.0);

        // some sprites should be flipped
        let flipped = rng.gen_bool(0.5);

        let transform = Transform::from_xyz(pos.0, pos.1, 0.0);

        let entity = commands
            .spawn((
                Contributor { name, hue },
                Velocity {
                    translation: velocity,
                    rotation: -dir * 5.0,
                },
                SpriteBundle {
                    sprite: Sprite {
                        custom_size: Some(Vec2::new(1.0, 1.0) * SPRITE_SIZE),
                        color: Color::hsla(hue, SATURATION_DESELECTED, LIGHTNESS_DESELECTED, ALPHA),
                        flip_x: flipped,
                        ..default()
                    },
                    texture: texture_handle.clone(),
                    transform,
                    ..default()
                },
            ))
            .id();

        contributor_selection.order.push(entity);
    }

    contributor_selection.order.shuffle(&mut rng);

    commands.insert_resource(contributor_selection);
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn(Camera2dBundle::default());

    commands.spawn((
        TextBundle::from_sections([
            TextSection::new(
                "Contributor showcase",
                TextStyle {
                    font: asset_server.load("fonts/FiraSans-Bold.ttf"),
                    font_size: 60.0,
                    ..default()
                },
            ),
            TextSection::from_style(TextStyle {
                font: asset_server.load("fonts/FiraSans-Bold.ttf"),
                font_size: 60.0,
                ..default()
            }),
        ])
        .with_style(Style {
            align_self: AlignSelf::FlexEnd,
            ..default()
        }),
        ContributorDisplay,
    ));
}

/// Finds the next contributor to display and selects the entity
fn select_system(
    mut timer: ResMut<SelectionState>,
    mut contributor_selection: ResMut<ContributorSelection>,
    mut text_query: Query<&mut Text, With<ContributorDisplay>>,
    mut query: Query<(&Contributor, &mut Sprite, &mut Transform)>,
    time: Res<Time>,
) {
    if !timer.timer.tick(time.delta()).just_finished() {
        return;
    }
    if !timer.has_triggered {
        let mut text = text_query.single_mut();
        text.sections[0].value = "Contributor: ".to_string();

        timer.has_triggered = true;
    }

    let entity = contributor_selection.order[contributor_selection.idx];
    if let Ok((contributor, mut sprite, mut transform)) = query.get_mut(entity) {
        deselect(&mut sprite, contributor, &mut transform);
    }

    if (contributor_selection.idx + 1) < contributor_selection.order.len() {
        contributor_selection.idx += 1;
    } else {
        contributor_selection.idx = 0;
    }

    let entity = contributor_selection.order[contributor_selection.idx];

    if let Ok((contributor, mut sprite, mut transform)) = query.get_mut(entity) {
        let mut text = text_query.single_mut();
        select(&mut sprite, contributor, &mut transform, &mut text);
    }
}

/// Change the tint color to the "selected" color, bring the object to the front
/// and display the name.
fn select(
    sprite: &mut Sprite,
    contributor: &Contributor,
    transform: &mut Transform,
    text: &mut Text,
) {
    sprite.color = Color::hsla(
        contributor.hue,
        SATURATION_SELECTED,
        LIGHTNESS_SELECTED,
        ALPHA,
    );

    transform.translation.z = 100.0;

    text.sections[1].value.clone_from(&contributor.name);
    text.sections[1].style.color = sprite.color;
}

/// Change the modulate color to the "deselected" color and push
/// the object to the back.
fn deselect(sprite: &mut Sprite, contributor: &Contributor, transform: &mut Transform) {
    sprite.color = Color::hsla(
        contributor.hue,
        SATURATION_DESELECTED,
        LIGHTNESS_DESELECTED,
        ALPHA,
    );

    transform.translation.z = 0.0;
}

/// Applies gravity to all entities with velocity
fn velocity_system(time: Res<Time>, mut velocity_query: Query<&mut Velocity>) {
    let delta = time.delta_seconds();

    for mut velocity in &mut velocity_query {
        velocity.translation.y -= GRAVITY * delta;
    }
}

/// Checks for collisions of contributor-birds.
///
/// On collision with left-or-right wall it resets the horizontal
/// velocity. On collision with the ground it applies an upwards
/// force.
fn collision_system(
    windows: Query<&Window>,
    mut query: Query<(&mut Velocity, &mut Transform), With<Contributor>>,
) {
    let window = windows.single();

    let ceiling = window.height() / 2.;
    let ground = -window.height() / 2.;

    let wall_left = -window.width() / 2.;
    let wall_right = window.width() / 2.;

    // The maximum height the birbs should try to reach is one birb below the top of the window.
    let max_bounce_height = (window.height() - SPRITE_SIZE * 2.0).max(0.0);

    let mut rng = rand::thread_rng();

    for (mut velocity, mut transform) in &mut query {
        let left = transform.translation.x - SPRITE_SIZE / 2.0;
        let right = transform.translation.x + SPRITE_SIZE / 2.0;
        let top = transform.translation.y + SPRITE_SIZE / 2.0;
        let bottom = transform.translation.y - SPRITE_SIZE / 2.0;

        // clamp the translation to not go out of the bounds
        if bottom < ground {
            transform.translation.y = ground + SPRITE_SIZE / 2.0;

            // How high this birb will bounce.
            let bounce_height = rng.gen_range((max_bounce_height * 0.4)..=max_bounce_height);

            // Apply the velocity that would bounce the birb up to bounce_height.
            velocity.translation.y = (bounce_height * GRAVITY * 2.).sqrt();
        }
        if top > ceiling {
            transform.translation.y = ceiling - SPRITE_SIZE / 2.0;
            velocity.translation.y *= -1.0;
        }
        // on side walls flip the horizontal velocity
        if left < wall_left {
            transform.translation.x = wall_left + SPRITE_SIZE / 2.0;
            velocity.translation.x *= -1.0;
            velocity.rotation *= -1.0;
        }
        if right > wall_right {
            transform.translation.x = wall_right - SPRITE_SIZE / 2.0;
            velocity.translation.x *= -1.0;
            velocity.rotation *= -1.0;
        }
    }
}

/// Apply velocity to positions and rotations.
fn move_system(time: Res<Time>, mut query: Query<(&Velocity, &mut Transform)>) {
    let delta = time.delta_seconds();

    for (velocity, mut transform) in &mut query {
        transform.translation += delta * velocity.translation;
        transform.rotate_z(velocity.rotation * delta);
    }
}

#[derive(Debug, thiserror::Error)]
enum LoadContributorsError {
    #[error("An IO error occurred while reading the git log.")]
    Io(#[from] io::Error),
    #[error("The CARGO_MANIFEST_DIR environment variable was not set.")]
    Var(#[from] VarError),
    #[error("The git process did not return a stdout handle.")]
    Stdout,
}

/// Get the names of all contributors from the git log.
///
/// The names are deduplicated.
/// This function only works if `git` is installed and
/// the program is run through `cargo`.
fn contributors() -> Result<Contributors, LoadContributorsError> {
    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR")?;

    let mut cmd = std::process::Command::new("git")
        .args(["--no-pager", "log", "--pretty=format:%an"])
        .current_dir(manifest_dir)
        .stdout(Stdio::piped())
        .spawn()?;

    let stdout = cmd.stdout.take().ok_or(LoadContributorsError::Stdout)?;

    let contributors = BufReader::new(stdout)
        .lines()
        .map_while(|x| x.ok())
        .collect();

    Ok(contributors)
}