First person controller

use bevy::input::mouse::MouseMotion;
use bevy::prelude::*;
use bevy::window::CursorGrabMode;

#[derive(Component)]
struct Player;

#[derive(Component)]
struct CameraSpeed(f32);

fn main() {
    App::new()
        .insert_resource(Msaa::Sample4)
        .add_plugins(DefaultPlugins.set(WindowPlugin {
            primary_window: Some(Window {
                title: "Zombie Mayhem".into(),
                mode: bevy::window::WindowMode::Fullscreen,
                ..Default::default()
            }),
            ..Default::default()
        }))
        .add_systems(Startup, setup)
        .add_systems(Update, (cursor_grab_system, look_y))
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    //floor
    commands.spawn(PbrBundle {
        mesh: meshes.add(Mesh::from(shape::Plane::from_size(16.0))),
        material: materials.add(Color::rgb(1., 0.9, 0.9).into()),
        transform: Transform::from_xyz(0., 0., 0.),
        ..Default::default()
    });
    //Cube
    commands.spawn(PbrBundle {
        mesh: meshes.add(Mesh::from(shape::Cube::new(1.))),
        material: materials.add(Color::rgb(1., 0.9, 0.9).into()),
        transform: Transform::from_xyz(0., 2., -10.),
        ..Default::default()
    });
    // light
    commands.spawn(PointLightBundle {
        point_light: PointLight {
            intensity: 1500.0,
            shadows_enabled: true,
            ..default()
        },
        transform: Transform::from_xyz(4.0, 8.0, 4.0),
        ..default()
    });

    // Player
    commands
        .spawn((Player, Transform::from_xyz(0., 0., 0.)))
        .with_children(|parent| {
            parent
                .spawn(Camera3dBundle {
                    transform: Transform::from_xyz(0., 4., 0.0),
                    ..Default::default()
                })
                .insert(CameraSpeed(4.));
        });
}

fn cursor_grab_system(
    mut windows: Query<&mut Window>,
    btn: Res<Input<MouseButton>>,
    key: Res<Input<KeyCode>>,
) {
    for mut window in &mut windows {
        if btn.just_pressed(MouseButton::Left) {
            // if you want to use the cursor, but not let it leave the window,
            // use `Confined` mode:
            window.cursor.grab_mode = CursorGrabMode::Confined;

            // also hide the cursor
            window.cursor.visible = false;
        }
        if key.just_pressed(KeyCode::Escape) {
            window.cursor.grab_mode = CursorGrabMode::None;
            window.cursor.visible = true;
        }
    }
}

fn look_y(
    mut cam_query: Query<(&mut Transform, &CameraSpeed, &Parent), With<Camera3d>>,
    mut player_query: Query<&mut Transform, Without<Camera3d>>,
    windows: Query<&Window>,
    mut mouse_event: EventReader<MouseMotion>,
    time: Res<Time>,
) {
    for (mut cam, spd, parent) in &mut cam_query {
        let mut player = player_query.get_mut(parent.get()).unwrap();
        for window in &windows {
            if !window.cursor.visible {
                for event in mouse_event.read() {
                    println!("X:{} Y:{}", event.delta.x, event.delta.y);
                    // Rotate by mouse movement
                    player.rotate_y(-event.delta.x * spd.0 * time.delta_seconds());
                    cam.rotate_x(-event.delta.y * spd.0 * time.delta_seconds());
                }
            }
        }
    }
}