//! Demonstrates how lighting is affected by different radius of point lights.

use bevy::prelude::*;

fn main() {
    App::new()
        .insert_resource(AmbientLight {
            brightness: 60.0,
            ..default()
        })
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(0.2, 1.5, 2.5).looking_at(Vec3::ZERO, Vec3::Y),
    ));

    // plane
    commands.spawn((
        Mesh3d(meshes.add(Plane3d::default().mesh().size(100.0, 100.0))),
        MeshMaterial3d(materials.add(StandardMaterial {
            base_color: Color::srgb(0.2, 0.2, 0.2),
            perceptual_roughness: 0.08,
            ..default()
        })),
    ));

    const COUNT: usize = 6;
    let position_range = -2.0..2.0;
    let radius_range = 0.0..0.4;
    let pos_len = position_range.end - position_range.start;
    let radius_len = radius_range.end - radius_range.start;
    let mesh = meshes.add(Sphere::new(1.0).mesh().uv(120, 64));

    for i in 0..COUNT {
        let percent = i as f32 / COUNT as f32;
        let radius = radius_range.start + percent * radius_len;

        // sphere light
        commands
            .spawn((
                Mesh3d(mesh.clone()),
                MeshMaterial3d(materials.add(StandardMaterial {
                    base_color: Color::srgb(0.5, 0.5, 1.0),
                    unlit: true,
                    ..default()
                })),
                Transform::from_xyz(position_range.start + percent * pos_len, 0.3, 0.0)
                    .with_scale(Vec3::splat(radius)),
            ))
            .with_child(PointLight {
                radius,
                color: Color::srgb(0.2, 0.2, 1.0),
                ..default()
            });
    }
}