outfly/src/camera.rs

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//       +                  +                +             ███
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//
// This module manages the game's viewport, handles camera- and
// movement-related keyboard input, and provides some camera-
// related computation functions.

use bevy::prelude::*;
use bevy::input::mouse::{MouseMotion, MouseWheel};
use bevy::window::PrimaryWindow;
use bevy::core_pipeline::bloom::{BloomCompositeMode, BloomSettings};
use bevy::core_pipeline::tonemapping::Tonemapping;
use bevy::pbr::{CascadeShadowConfigBuilder, DirectionalLightShadowMap};
use bevy::transform::TransformSystem;
use bevy::math::{DVec3, DQuat};
use bevy_xpbd_3d::prelude::*;
use std::f32::consts::PI;
use std::f64::consts::PI as PI64;
use crate::{actor, audio, hud, var};

pub const INITIAL_ZOOM_LEVEL: f64 = 10.0;

pub struct CameraPlugin;

impl Plugin for CameraPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, setup_camera);
        app.add_systems(Update, handle_input);
        app.add_systems(Update, update_map_only_object_visibility);
        app.add_systems(Update, manage_player_actor.after(handle_input));
        app.add_systems(PostUpdate, sync_camera_to_player
            .after(PhysicsSet::Sync)
            .after(apply_input_to_player)
            .before(TransformSystem::TransformPropagate));
        app.add_systems(Update, update_map_camera);
        app.add_systems(Update, update_fov);
        app.add_systems(PostUpdate, apply_input_to_player
            .after(PhysicsSet::Sync)
            .before(TransformSystem::TransformPropagate));
        app.insert_resource(MapCam::default());
    }
}

#[derive(Component)]
pub struct ShowOnlyInMap {
    pub min_distance: f64,
    pub distance_to_id: String,
}

#[derive(Resource)]
pub struct MapCam {
    pub initialized: bool,
    pub zoom_level: f64,
    pub target_zoom_level: f64,
    pub pitch: f64,
    pub yaw: f64,
    pub offset_x: f64,
    pub offset_z: f64,
    pub center: DVec3,
}
impl Default for MapCam {
    fn default() -> Self {
        Self {
            initialized: false,
            zoom_level: 2.0,
            target_zoom_level: INITIAL_ZOOM_LEVEL,
            pitch: PI64 * 0.3,
            yaw: 0.0,
            offset_x: 0.0,
            offset_z: 0.0,
            center: DVec3::new(0.0, 0.0, 0.0),
        }
    }
}

pub fn setup_camera(
    mut commands: Commands,
    settings: Res<var::Settings>,
) {
    // Add player
    commands.spawn((
        Camera3dBundle {
            camera: Camera {
                hdr: true, // HDR is required for bloom
                clear_color: ClearColorConfig::Custom(Color::BLACK),
                ..default()
            },
            tonemapping: Tonemapping::TonyMcMapface,
            transform: Transform::from_xyz(0.0, 0.0, 8.0).looking_at(Vec3::ZERO, Vec3::Y),
            ..default()
        },
        BloomSettings {
            composite_mode: BloomCompositeMode::EnergyConserving,
            ..default()
        },
    ));

    // Add Light from the Sun
    commands.spawn(DirectionalLightBundle {
        directional_light: DirectionalLight {
            illuminance: 3000.0,
            shadows_enabled: settings.shadows_sun,
            ..default()
        },
        transform: Transform::from_rotation(Quat::from_rotation_y(PI/2.0)),
        cascade_shadow_config: CascadeShadowConfigBuilder {
            num_cascades: 4,
            minimum_distance: 0.1,
            maximum_distance: 5000.0,
            ..default()
        }.into(),
        ..default()
    });

    commands.insert_resource(DirectionalLightShadowMap {
        size: settings.shadowmap_resolution,
    });
}

pub fn sync_camera_to_player(
    settings: Res<var::Settings>,
    mut q_camera: Query<&mut Transform, (With<Camera>, Without<actor::PlayerCamera>)>,
    q_playercam: Query<(&actor::Actor, &Transform), (With<actor::PlayerCamera>, Without<Camera>)>,
) {
    if settings.map_active || q_camera.is_empty() || q_playercam.is_empty() {
        return;
    }
    let mut camera_transform = q_camera.get_single_mut().unwrap();
    let (actor, player_transform) = q_playercam.get_single().unwrap();

    // Rotation
    camera_transform.rotation = player_transform.rotation * Quat::from_array([0.0, -1.0, 0.0, 0.0]);

    // Translation
    if settings.third_person {
        camera_transform.translation = player_transform.translation + camera_transform.rotation * (actor.camdistance * Vec3::new(0.0, 0.2, 1.0));
    }
    else {
        camera_transform.translation = player_transform.translation;
    }
}

pub fn update_map_camera(
    settings: Res<var::Settings>,
    mut mapcam: ResMut<MapCam>,
    mut q_camera: Query<&mut Transform, (With<Camera>, Without<actor::PlayerCamera>)>,
    q_playercam: Query<&Transform, (With<actor::PlayerCamera>, Without<Camera>)>,
    q_target: Query<&Transform, (With<hud::IsTargeted>, Without<Camera>, Without<actor::PlayerCamera>)>,
    q_target_changed: Query<(), Changed<hud::IsTargeted>>,
    mut mouse_events: EventReader<MouseMotion>,
    mut er_mousewheel: EventReader<MouseWheel>,
    keyboard_input: Res<ButtonInput<KeyCode>>,
) {
    if !settings.map_active || q_camera.is_empty() || q_playercam.is_empty() {
        return;
    }
    let mut camera_transform = q_camera.get_single_mut().unwrap();
    let player_transform = q_playercam.get_single().unwrap();
    let target = if let Ok(target) = q_target.get_single() {
        target
    } else {
        player_transform
    };

    // Get mouse movement
    let mut mouse_delta = Vec2::ZERO;
    for mouse_event in mouse_events.read() {
        mouse_delta += mouse_event.delta;
    }
    // NOTE: we need to subtract a bit from PI/2, otherwise the "up"
    // direction parameter for the Transform.look_at function is ambiguous
    // at the extreme values and the orientation will flicker back/forth.
    let epsilon = 0.001;
    let min_zoom: f64 = target.scale.x as f64 * 2.0;
    let max_zoom: f64 = 17e18; // at this point, camera starts glitching
    mapcam.pitch = (mapcam.pitch + mouse_delta.y as f64 / 180.0 * settings.mouse_sensitivity as f64).clamp(-PI64 / 2.0 + epsilon, PI64 / 2.0 - epsilon);
    mapcam.yaw += mouse_delta.x as f64 / 180.0 * settings.mouse_sensitivity as f64;

    // Reset movement offset if target changes
    if !q_target_changed.is_empty() {
        mapcam.offset_x = 0.0;
        mapcam.offset_z = 0.0;
    }

    // Get keyboard movement
    let mut offset_x: f64 = 0.0;
    let mut offset_z: f64 = 0.0;
    if keyboard_input.pressed(settings.key_forward) {
        offset_x -= 1.0;
    }
    if keyboard_input.pressed(settings.key_back) {
        offset_x += 1.0;
    }
    if keyboard_input.pressed(settings.key_right) {
        offset_z -= 1.0;
    }
    if keyboard_input.pressed(settings.key_left) {
        offset_z += 1.0;
    }
    if keyboard_input.pressed(settings.key_stop) {
        mapcam.offset_x = 0.0;
        mapcam.offset_z = 0.0;
    }

    // Update zoom level
    if !mapcam.initialized {
        let factor: f64 = if target == player_transform { 7.0 } else { 1.0 };
        mapcam.target_zoom_level *= target.scale.x as f64 * factor;
        mapcam.zoom_level *= target.scale.x as f64 * factor;
        mapcam.initialized = true;
    }
    let mut change_zoom: f64 = 0.0;
    if keyboard_input.pressed(settings.key_map_zoom_out) {
        change_zoom += 0.5;
    }
    if keyboard_input.pressed(settings.key_map_zoom_in) {
        change_zoom -= 0.5;
    }
    for wheel_event in er_mousewheel.read() {
        change_zoom -= wheel_event.y as f64 * 3.0;
    }
    mapcam.target_zoom_level = (mapcam.target_zoom_level * 1.1f64.powf(change_zoom)).clamp(min_zoom, max_zoom);
    let zoom_speed = 0.05; // should be between 0.0001 (slow) and 1.0 (instant)
    mapcam.zoom_level = (zoom_speed * mapcam.target_zoom_level + (1.0 - zoom_speed) * mapcam.zoom_level).clamp(min_zoom, max_zoom);

    // Update point of view
    let pov_rotation = DQuat::from_euler(EulerRot::XYZ, 0.0, mapcam.yaw as f64, mapcam.pitch as f64);
    let offset = DVec3::new(mapcam.offset_x, 0.0, mapcam.offset_z);
    let point_of_view = offset + pov_rotation * (mapcam.zoom_level as f64 * DVec3::new(1.0, 0.0, 0.0));

    // Update movement offset
    let mut direction = pov_rotation * DVec3::new(offset_x, 0.0, offset_z);
    let speed = direction.length();
    direction.y = 0.0;
    let direction = speed * direction.normalize_or_zero();

    mapcam.offset_x += 0.01 * (direction.x * mapcam.zoom_level);
    mapcam.offset_z += 0.01 * (direction.z * mapcam.zoom_level);

    // Apply updates to camera
    mapcam.center = target.translation.as_dvec3() + offset;
    camera_transform.translation = target.translation + point_of_view.as_vec3();
    camera_transform.look_at(mapcam.center.as_vec3(), Vec3::Y);
}

pub fn update_fov(
    q_player: Query<&actor::ExperiencesGForce, With<actor::Player>>,
    mouse_input: Res<ButtonInput<MouseButton>>,
    mut settings: ResMut<var::Settings>,
    mut q_camera: Query<&mut Projection, With<Camera>>,
) {
    if let (Ok(gforce), Ok(mut projection)) = (q_player.get_single(), q_camera.get_single_mut())
    {
        let fov: f32;
        if settings.hud_active && mouse_input.pressed(settings.key_zoom) {
            fov = settings.zoom_fov.to_radians();
            if !settings.is_zooming {
                settings.is_zooming = true;
            }
        } else {
            fov = (gforce.visual_effect.clamp(0.0, 1.0) * settings.fov_highspeed + settings.fov).to_radians();
            if settings.is_zooming {
                settings.is_zooming = false;
            }
        };
        *projection = Projection::Perspective(PerspectiveProjection { fov: fov, ..default() });
    }
}

pub fn handle_input(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mut q_light: Query<&mut DirectionalLight>,
    mut settings: ResMut<var::Settings>,
    mut mapcam: ResMut<MapCam>,
    mut ew_sfx: EventWriter<audio::PlaySfxEvent>,
    mut ew_updateoverlays: EventWriter<hud::UpdateOverlayVisibility>,
) {
    if keyboard_input.just_pressed(settings.key_camera) {
        settings.third_person ^= true;
    }
    if keyboard_input.just_pressed(settings.key_shadows) {
        ew_sfx.send(audio::PlaySfxEvent(audio::Sfx::Click));
        settings.shadows_sun ^= true;
        for mut light in &mut q_light {
            light.shadows_enabled = settings.shadows_sun;
        }
    }
    if keyboard_input.just_pressed(settings.key_map) {
        settings.map_active ^= true;
        if settings.map_active {
            ew_sfx.send(audio::PlaySfxEvent(audio::Sfx::Woosh));
        }
        *mapcam = MapCam::default();
        ew_updateoverlays.send(hud::UpdateOverlayVisibility);
    }
    if keyboard_input.just_pressed(settings.key_rotation_stabilizer) {
        ew_sfx.send(audio::PlaySfxEvent(audio::Sfx::Switch));
        settings.rotation_stabilizer_active ^= true;
    }
}

fn manage_player_actor(
    mut commands: Commands,
    settings: Res<var::Settings>,
    mut q_playercam: Query<&mut Visibility, With<actor::PlayerCamera>>,
    mut q_hiddenplayer: Query<(Entity, &mut Visibility, &mut Position, &mut Rotation, &mut LinearVelocity, &mut AngularVelocity, Option<&mut actor::ExperiencesGForce>, Option<&actor::JustNowEnteredVehicle>), (With<actor::Player>, Without<actor::PlayerCamera>)>,
    q_ride: Query<(&Transform, &Position, &Rotation, &LinearVelocity, &AngularVelocity), (With<actor::PlayerDrivesThis>, Without<actor::Player>)>,
) {
    for mut vis in &mut q_playercam {
        if settings.third_person || settings.map_active {
            *vis = Visibility::Inherited;
        }
        else {
            *vis = Visibility::Hidden;
        }
    }
    for (entity, mut vis, mut pos, mut rot, mut v, mut angv, mut gforce, entering) in &mut q_hiddenplayer {
        // If we are riding a vehicle, place the player at the position where
        // it would be after exiting the vehicle.
        // I would rather place it in the center of the vehicle, but at the time
        // of writing, I couldn't set the position/rotation of the player *during*
        // exiting the vehicle, so I'm doing it here instead, as a workaround.
        *vis = Visibility::Hidden;
        if let Ok((ride_trans, ride_pos, ride_rot, ride_v, ride_angv)) = q_ride.get_single() {
            pos.0 = ride_pos.0 + DVec3::from(ride_trans.rotation * Vec3::new(0.0, 0.0, ride_trans.scale.z * 2.0));
            rot.0 = ride_rot.0 * DQuat::from_array([-1.0, 0.0, 0.0, 0.0]);
            *v = ride_v.clone();
            *angv = ride_angv.clone();

            // I really don't want people to die from the g-forces of entering
            // vehicles at high relative speed, even though they probably should.
            if let (Some(gforce), Some(_)) = (&mut gforce, entering) {
                gforce.last_linear_velocity = v.0;
                commands.entity(entity).remove::<actor::JustNowEnteredVehicle>();
            }
        }
    }
}

#[allow(clippy::too_many_arguments)]
pub fn apply_input_to_player(
    time: Res<Time>,
    settings: Res<var::Settings>,
    windows: Query<&Window, With<PrimaryWindow>>,
    mut mouse_events: EventReader<MouseMotion>,
    key_input: Res<ButtonInput<KeyCode>>,
    thruster_sound_controller: Query<&AudioSink, With<audio::ComponentThrusterSound>>,
    rocket_sound_controller: Query<&AudioSink, With<audio::ComponentRocketSound>>,
    ion_sound_controller: Query<&AudioSink, With<audio::ComponentIonSound>>,
    electricmotor_sound_controller: Query<&AudioSink, With<audio::ComponentElectricMotorSound>>,
    q_target: Query<&LinearVelocity, (With<hud::IsTargeted>, Without<actor::PlayerCamera>)>,
    mut q_playercam: Query<(
            &Transform,
            &mut actor::Engine,
            &mut AngularVelocity,
            &mut LinearVelocity,
            &mut ExternalTorque,
            Option<&actor::PlayerDrivesThis>,
        ), (With<actor::PlayerCamera>, Without<Camera>)>,
) {
    if settings.map_active {
        return;
    }
    let dt = time.delta_seconds();
    let mut play_thruster_sound = false;
    let mut axis_input: DVec3 = DVec3::ZERO;

    let (win_res_x, win_res_y): (f32, f32);
    let mut focused = true;
    if let Ok(window) = &windows.get_single() {
        focused = window.focused;
        win_res_x = window.resolution.width();
        win_res_y = window.resolution.height();
    }
    else {
        win_res_x = 1920.0;
        win_res_y = 1050.0;
    }

    let target_v: DVec3 = if let Ok(target) = q_target.get_single() {
        target.0
    } else {
        DVec3::splat(0.0)
    };

    if let Ok((player_transform, mut engine, mut angularvelocity, mut v, mut torque, bike)) = q_playercam.get_single_mut() {
        // Handle key input
        if focused {
            if key_input.pressed(settings.key_forward) {
                axis_input.z += 1.2;
            }
            if key_input.pressed(settings.key_back) {
                axis_input.z -= 1.2;
            }
            if key_input.pressed(settings.key_right) {
                axis_input.x -= 1.2;
            }
            if key_input.pressed(settings.key_left) {
                axis_input.x += 1.2;
            }
            if key_input.pressed(settings.key_up) {
                axis_input.y += 1.2;
            }
            if key_input.pressed(settings.key_down) {
                axis_input.y -= 1.2;
            }
            if key_input.pressed(settings.key_stop) {
                let stop_direction = (target_v - v.0).normalize();
                if stop_direction.length_squared() > 0.3 {
                    axis_input += 1.0 * DVec3::from(player_transform.rotation.inverse() * stop_direction.as_vec3());
                }
            }
        }
        // In typical games we would normalize the input vector so that diagonal movement is as
        // fast as forward or sideways movement.  But here, we merely clamp each direction to an
        // absolute maximum of 1, since every thruster can be used separately. If the forward
        // thrusters and the leftward thrusters are active at the same time, then of course the
        // total diagonal acceleration is faster than the forward acceleration alone.
        axis_input = axis_input.clamp(DVec3::splat(-1.0), DVec3::splat(1.0));

        // Apply movement update
        let forward_factor = engine.current_warmup * (if axis_input.z > 0.0 {
            engine.thrust_forward
        } else {
            engine.thrust_back
        });
        let right_factor = engine.thrust_sideways * engine.current_warmup;
        let up_factor = engine.thrust_sideways * engine.current_warmup;
        let factor = DVec3::new(right_factor as f64, up_factor as f64, forward_factor as f64);

        if axis_input.length_squared() > 0.003 {
            let acceleration_global: DVec3 = DVec3::from(player_transform.rotation * (axis_input * factor).as_vec3());
            let mut acceleration_total: DVec3 = (actor::ENGINE_SPEED_FACTOR * dt) as f64 * acceleration_global;
            let threshold = 1e-5;
            if key_input.pressed(settings.key_stop) {
                // Decelerate (or match velocity to target_v)
                let dv = v.0 - target_v;
                for i in 0..3 {
                    if dv[i].abs() < threshold {
                        v[i] = target_v[i];
                    }
                    else if dv[i].signum() != (dv[i] + acceleration_total[i]).signum() {
                        // Almost stopped, but we overshot v=0
                        v[i] = target_v[i];
                        acceleration_total[i] = 0.0;
                    }
                }
            }
            // TODO: handle mass
            v.0 += acceleration_total;
            engine.current_warmup = (engine.current_warmup + dt / engine.warmup_seconds).clamp(0.0, 1.0);
            play_thruster_sound = true;
        }
        else {
            engine.current_warmup = (engine.current_warmup - dt / engine.warmup_seconds).clamp(0.0, 1.0);
        }

        // Handle mouse input and mouse-like key bindings
        let mut play_reactionwheel_sound = false;
        let mut mouse_delta = Vec2::ZERO;
        let mut pitch_yaw_rot = Vec3::ZERO;
        let sensitivity_factor = if settings.is_zooming { settings.zoom_sensitivity_factor } else { 1.0 };
        let mouseless_sensitivity = 8.0 * sensitivity_factor;
        let mouseless_rotation_sensitivity = 40.0 * sensitivity_factor;
        if key_input.pressed(settings.key_mouseup) {
            pitch_yaw_rot[0] -= mouseless_sensitivity;
        }
        if key_input.pressed(settings.key_mousedown) {
            pitch_yaw_rot[0] += mouseless_sensitivity;
        }
        if key_input.pressed(settings.key_mouseleft) {
            pitch_yaw_rot[1] += mouseless_sensitivity; }
        if key_input.pressed(settings.key_mouseright) {
            pitch_yaw_rot[1] -= mouseless_sensitivity;
        }
        if key_input.pressed(settings.key_rotateleft) {
            pitch_yaw_rot[2] -= mouseless_rotation_sensitivity;
        }
        if key_input.pressed(settings.key_rotateright) {
            pitch_yaw_rot[2] += mouseless_rotation_sensitivity;
        }
        for mouse_event in mouse_events.read() {
            mouse_delta += mouse_event.delta;
        }
        if mouse_delta != Vec2::ZERO {
            if key_input.pressed(settings.key_rotate) {
                pitch_yaw_rot[2] += 1000.0 * mouse_delta.x / win_res_x;
            } else {
                pitch_yaw_rot[0] += 1000.0 * mouse_delta.y / win_res_y;
                pitch_yaw_rot[1] -= 1000.0 * mouse_delta.x / win_res_x;
            }
        }

        let angular_slowdown: f64 = if settings.rotation_stabilizer_active {
            (2.0 - engine.reaction_wheels.powf(0.01).clamp(1.001, 1.1)) as f64
        } else {
            1.0
        };
        if pitch_yaw_rot.length_squared() > 1.0e-18 {
            play_reactionwheel_sound = true;
            pitch_yaw_rot *= settings.mouse_sensitivity * sensitivity_factor * engine.reaction_wheels;
            torque.apply_torque(DVec3::from(
                    player_transform.rotation * Vec3::new(
                        pitch_yaw_rot[0],
                        pitch_yaw_rot[1],
                        pitch_yaw_rot[2])));
            angularvelocity.0 *= angular_slowdown.clamp(0.97, 1.0) as f64;
        }
        else {
            if angularvelocity.length_squared() > 1.0e-18 {
                angularvelocity.0 *= angular_slowdown;
            }
            else {
                angularvelocity.0 = DVec3::splat(0.0);
            }
        }

        // Play sound effects
        if let Ok(sink) = electricmotor_sound_controller.get_single() {
            let volume = sink.volume();
            let speed = sink.speed();
            let action = pitch_yaw_rot.length_squared().powf(0.2) * 0.0005;
            if play_reactionwheel_sound && !settings.mute_sfx && bike.is_some() {
                sink.set_volume((volume + action).clamp(0.0, 1.0));
                sink.set_speed((speed + action * 0.2).clamp(0.2, 0.5));
                sink.play()
            } else {
                if volume <= 0.01 {
                    sink.pause()
                } else {
                    sink.set_volume((volume - 0.01).clamp(0.0, 1.0));
                    sink.set_speed((speed - 0.03).clamp(0.2, 0.5));
                }
            }
        }
        let sinks = vec![
            (1.2, actor::EngineType::Monopropellant, thruster_sound_controller.get_single()),
            (1.0, actor::EngineType::Rocket, rocket_sound_controller.get_single()),
            (1.4, actor::EngineType::Ion, ion_sound_controller.get_single()),
        ];
        let seconds_to_max_vol = 0.05;
        let seconds_to_min_vol = 0.05;
        for sink_data in sinks {
            if let (vol_boost, engine_type, Ok(sink)) = sink_data {
                if settings.mute_sfx {
                    sink.pause();
                }
                else {
                    let volume = sink.volume();
                    if engine.engine_type == engine_type {
                        if play_thruster_sound {
                            sink.play();
                            if volume < 1.0 {
                                let maxvol = vol_boost;
                                //let maxvol = engine.current_warmup * vol_boost;
                                sink.set_volume((volume + dt / seconds_to_max_vol).clamp(0.0, maxvol));
                            }
                        } else {
                            sink.set_volume((volume - dt / seconds_to_min_vol).clamp(0.0, 1.0));
                        }
                    }
                    else if volume > 0.0 {
                        sink.set_volume((volume - dt / seconds_to_min_vol).clamp(0.0, 1.0));
                    }
                    if volume < 0.0001 {
                        sink.pause();
                    }
                }
            }
        }
    }
}

pub fn update_map_only_object_visibility(
    settings: Res<var::Settings>,
    q_camera: Query<&Transform, With<Camera>>,
    q_player: Query<&Position, With<actor::PlayerCamera>>,
    mut q_onlyinmap: Query<(&mut Visibility, &ShowOnlyInMap), Without<Camera>>,
    id2pos: Res<actor::Id2Pos>,
) {
    if q_camera.is_empty() || q_player.is_empty() {
        return;
    }
    let cam: &Transform = q_camera.get_single().unwrap();
    let player_pos: &Position = q_player.get_single().unwrap();
    let cam_pos: Vec3 = cam.translation + player_pos.as_vec3();
    for (mut vis, onlyinmap) in &mut q_onlyinmap {
        if settings.map_active && settings.hud_active {
            if let Some(pos) = id2pos.0.get(&onlyinmap.distance_to_id) {
                let dist = cam_pos.distance(pos.as_vec3());
                if dist >= onlyinmap.min_distance as f32 {
                    *vis = Visibility::Inherited;
                }
                else {
                    *vis = Visibility::Hidden;
                }
            } else {
                error!("Failed get position of actor ID '{}'", &onlyinmap.distance_to_id);
                *vis = Visibility::Hidden;
            }
        } else {
            *vis = Visibility::Hidden;
        }
    }
}

// Find the closest world object that the player is looking at
#[inline]
pub fn find_closest_target<TargetSpecifier>(
    objects: Vec<(TargetSpecifier, &Transform)>,
    camera_transform: &Transform,
) -> (Option<TargetSpecifier>, f32)
    where TargetSpecifier: Clone
{
    let mut closest_entity: Option<TargetSpecifier> = None;
    let mut closest_distance: f32 = f32::MAX;
    let target_vector: Vec3 = (camera_transform.rotation * Vec3::new(0.0, 0.0, -1.0))
        .normalize_or_zero();
    for (entity, trans) in objects {
        // Use Transform instead of Position because we're basing this
        // not on the player mesh but on the camera, which doesn't have a position.
        let (angular_diameter, angle, distance) = calc_angular_diameter_known_target_vector(
                trans, camera_transform, &target_vector);
        if angle <= angular_diameter.clamp(0.01, PI) {
            // It's in the field of view!
            //commands.entity(entity).insert(IsTargeted);
        let distance_to_surface = distance - trans.scale.x;
            if distance_to_surface < closest_distance {
                closest_distance = distance_to_surface;
                closest_entity = Some(entity);
            }
        }
    }
    return (closest_entity, closest_distance);
}

#[inline]
pub fn calc_angular_diameter_known_target_vector(
    target: &Transform,
    camera: &Transform,
    target_vector: &Vec3,
) -> (f32, f32, f32) {
    let pos_vector: Vec3 = (target.translation - camera.translation)
        .normalize_or_zero();
    let cosine_of_angle: f32 = target_vector.dot(pos_vector);
    let angle: f32 = cosine_of_angle.acos();
    let distance: f32 = target.translation.distance(camera.translation);
    let leeway: f32 = 1.3;
    let angular_diameter: f32 = if distance > 0.0 {
        // Angular Diameter
        leeway * (target.scale[0] / distance).asin()
    }
    else {
        0.0
    };
    return (angular_diameter, angle, distance);
}

#[inline]
pub fn calc_angular_diameter(
    target: &Transform,
    camera: &Transform,
) -> (f32, f32, f32) {
    let target_vector: Vec3 = (camera.rotation * Vec3::new(0.0, 0.0, -1.0))
        .normalize_or_zero();
    return calc_angular_diameter_known_target_vector(target, camera, &target_vector);
}