Merge branch 'gravity'

README.md

@@ -35,6 +35,8 @@ The `SPACE` key helps you move more intuitively by slowing you down.  Hold it fo
 
 When you're ready, take a look around, explore the starting area. There is a friendly person floating nearby in a red space suit that would love to talk to you.
 
+The game is a bit dark, since it's meant to be played in the night. But maybe you're unlucky and you start with a planet or moon eclipsing the sun, making everything extra dark. (Yes, all celestial objects move in real time and have different positions depending on when you play.)  If it's too dark, try the flashlight (`f` key), turning off the shadows in the menu, and make sure that Augmented Reality is on (`TAB` key) which gives you a little extra light amplification.
+
 Press the `ESC` key for the menu to restart the game if you get lost, explore more key bindings, game features, and the **achievements** to get some guidance on what you can do in the game.
 
 But in the end, OutFly is an open world game with no true goals other than the ones you set for yourself.  Just lean back, get cozy, and drift towards whatever catches your eye :)

src/actor.rs

@@ -30,8 +30,9 @@ impl Plugin for ActorPlugin {
             (
                 update_physics_lifeforms,
                 update_power,
+                handle_gravity,
                 handle_wants_maxrotation,
-                handle_wants_maxvelocity,
+                handle_wants_maxvelocity.run_if(any_with_component::<WantsMaxVelocity>),
                 handle_wants_lookat.run_if(alive),
             ),
         );
@@ -118,6 +119,7 @@ pub struct ExperiencesGForce {
     pub visual_effect_threshold: f32,
     pub visual_effect: f32,
     pub last_linear_velocity: DVec3,
+    pub gravitational_component: DVec3,
     pub ignore_gforce_seconds: f32,
 }
 impl Default for ExperiencesGForce {
@@ -127,8 +129,9 @@ impl Default for ExperiencesGForce {
             damage_threshold: 100.0,
             visual_effect_threshold: 20.0,
             visual_effect: 0.0,
-            last_linear_velocity: DVec3::splat(0.0),
+            last_linear_velocity: DVec3::ZERO,
-            ignore_gforce_seconds: 0.0,
+            gravitational_component: DVec3::ZERO,
+            ignore_gforce_seconds: 0.01,
         }
     }
 }
@@ -156,7 +159,11 @@ pub struct WantsMaxVelocity(pub f64);
 #[derive(Component)]
 pub struct WantsToLookAt(pub String);
 #[derive(Component)]
+pub struct WantsMatchVelocityWith(pub String);
+#[derive(Component)]
 pub struct Identifier(pub String);
+#[derive(Component)]
+pub struct OrbitsJupiter;
 
 #[derive(Component)]
 pub struct LifeForm {
@@ -535,25 +542,53 @@ fn handle_wants_maxrotation(
     }
 }
 
+/// Slows down NPC's movement until they reach their target velocity.
 fn handle_wants_maxvelocity(
     time: Res<Time>,
-    mut query: Query<(&mut LinearVelocity, &Engine, &WantsMaxVelocity)>,
+    mut query: Query<(
+        &Position,
+        &mut LinearVelocity,
+        &Engine,
+        &WantsMaxVelocity,
+        Option<&OrbitsJupiter>,
+        Option<&WantsMatchVelocityWith>,
+    )>,
+    id2v: Res<game::Id2V>,
+    jupiter_pos: Res<game::JupiterPos>,
 ) {
     let dt = time.delta_seconds();
-    for (mut v, engine, maxv) in &mut query {
+    for (pos, mut v, engine, maxv, orbits_jupiter, matchwith) in &mut query {
-        let total = v.0.length();
+        let target_velocity = if let Some(matchwith) = matchwith {
-        if total <= maxv.0 + EPSILON {
+            if let Some(target_v) = id2v.0.get(&matchwith.0) {
-            if total > maxv.0 {
+                *target_v
-                v.0 = DVec3::splat(0.0);
+            } else {
+                warn!("Can't match velocity with nonexisting ID {}", matchwith.0);
+                continue;
+            }
+        } else if orbits_jupiter.is_some() {
+            let relative_pos = pos.0 - jupiter_pos.0;
+            nature::orbital_velocity(relative_pos, nature::JUPITER_MASS)
+        } else {
+            DVec3::ZERO
+        };
+        let relative_velocity = v.0 - target_velocity;
+        let relative_speed = relative_velocity.length();
+
+        if relative_speed <= maxv.0 + EPSILON {
+            // it's already pretty close to the target
+            if relative_speed > maxv.0 {
+                // but not quite the target, so let's set it to the target
+                v.0 = target_velocity;
             }
         } else {
+            // slow it down a little bit
             // TODO: respect engine parameters for different thrusts for different directions
             let avg_thrust =
                 (engine.thrust_forward + engine.thrust_back + engine.thrust_sideways) / 3.0;
-            let acceleration = (avg_thrust * dt) as f64 * -v.0;
+            let acceleration = (avg_thrust * dt) as f64 * -relative_velocity;
             v.0 += acceleration;
             if v.0.length() + EPSILON < acceleration.length() {
-                v.0 = DVec3::splat(0.0);
+                v.0 = target_velocity;
             }
         }
     }
@@ -610,8 +645,10 @@ fn handle_gforce(
     let dt = time.delta_seconds();
     let factor = 1.0 / dt / nature::EARTH_GRAVITY;
     for (v, mut hp, mut gforce) in &mut q_actor {
-        gforce.gforce = factor * (v.0 - gforce.last_linear_velocity).length() as f32;
+        gforce.gforce = factor
+            * (v.0 - gforce.last_linear_velocity - gforce.gravitational_component).length() as f32;
         gforce.last_linear_velocity = v.0;
+        gforce.gravitational_component = DVec3::ZERO;
         if gforce.ignore_gforce_seconds > 0.0 {
             gforce.ignore_gforce_seconds -= dt;
             continue;
@@ -632,3 +669,28 @@ fn handle_gforce(
         }
     }
 }
+
+fn handle_gravity(
+    time: Res<Time>,
+    mut q_pos: Query<
+        (
+            &Position,
+            &mut LinearVelocity,
+            Option<&mut ExperiencesGForce>,
+        ),
+        With<OrbitsJupiter>,
+    >,
+    jupiter_pos: Res<game::JupiterPos>,
+) {
+    let dt = time.delta_seconds() as f64;
+
+    // this assumes prograde orbits for every object
+    for (pos, mut v, gforce_maybe) in &mut q_pos {
+        let relative_pos = pos.0 - jupiter_pos.0;
+        let accel = dt * nature::gravitational_acceleration(relative_pos, nature::JUPITER_MASS);
+        if let Some(mut gforce) = gforce_maybe {
+            gforce.gravitational_component += accel;
+        }
+        v.0 += accel;
+    }
+}

src/camera.rs

@@ -416,6 +416,7 @@ pub fn apply_input_to_player(
     time: Res<Time>,
     mut commands: Commands,
     settings: Res<var::Settings>,
+    jupiter_pos: Res<game::JupiterPos>,
     windows: Query<&Window, With<PrimaryWindow>>,
     mut mouse_events: EventReader<MouseMotion>,
     key_input: Res<ButtonInput<KeyCode>>,
@@ -426,6 +427,7 @@ pub fn apply_input_to_player(
             Entity,
             &Transform,
             &mut actor::Engine,
+            &Position,
             &mut LinearVelocity,
             &mut ExternalTorque,
             Option<&actor::PlayerDrivesThis>,
@@ -451,15 +453,15 @@ pub fn apply_input_to_player(
         win_res_y = 1050.0;
     }
 
+    if let Ok((player_entity, player_transform, mut engine, pos, mut v, mut torque, bike)) =
+        q_playercam.get_single_mut()
+    {
         let target_v: DVec3 = if let Ok(target) = q_target.get_single() {
             target.0
         } else {
-        DVec3::splat(0.0)
+            let relative_pos = pos.0 - jupiter_pos.0;
+            nature::orbital_velocity(relative_pos, nature::JUPITER_MASS)
         };
-
-    if let Ok((player_entity, player_transform, mut engine, mut v, mut torque, bike)) =
-        q_playercam.get_single_mut()
-    {
         // Handle key input
         if focused {
             if key_input.pressed(settings.key_forward) || settings.cruise_control_active {

src/chat.rs

@@ -827,6 +827,7 @@ pub fn handle_chat_scripts(
     mut ew_effect: EventWriter<visual::SpawnEffectEvent>,
     mut ew_achievement: EventWriter<game::AchievementEvent>,
     id2pos: Res<game::Id2Pos>,
+    id2v: Res<game::Id2V>,
 ) {
     for script in er_chatscript.read() {
         // Parse the script string
@@ -892,15 +893,22 @@ pub fn handle_chat_scripts(
                             _ => None,
                         };
                         if let Some(station) = busstop {
-                            if let Some(target) = id2pos.0.get(&station.to_string()) {
+                            if let Some(target_pos) = id2pos.0.get(&station.to_string()) {
-                                pos.0 = *target + DVec3::new(0.0, -1000.0, 0.0);
+                                pos.0 = *target_pos + DVec3::new(0.0, -1000.0, 0.0);
-                                v.0 = DVec3::ZERO;
                             } else {
                                 error!(
                                     "Could not determine position of actor with ID: '{}'",
                                     station
                                 );
                             }
+                            if let Some(target_v) = id2v.0.get(&station.to_string()) {
+                                v.0 = *target_v;
+                            } else {
+                                error!(
+                                    "Could not determine velocity of actor with ID: '{}'",
+                                    station
+                                );
+                            }
                         } else {
                             error!("Invalid destination for cryotrip chat script: '{}'", param1);
                         }

src/cmd.rs

@@ -86,6 +86,7 @@ struct ParserState {
     wants_maxrotation: Option<f64>,
     wants_maxvelocity: Option<f64>,
     wants_tolookat_id: Option<String>,
+    wants_matchvelocity_id: Option<String>,
     collider_is_mesh: bool,
     collider_is_one_mesh_of_scene: bool,
     thrust_forward: f32,
@@ -143,6 +144,7 @@ impl Default for ParserState {
             wants_maxrotation: None,
             wants_maxvelocity: None,
             wants_tolookat_id: None,
+            wants_matchvelocity_id: None,
             collider_is_mesh: false,
             collider_is_one_mesh_of_scene: false,
             thrust_forward: default_engine.thrust_forward,
@@ -582,6 +584,10 @@ pub fn load_defs(mut ew_spawn: EventWriter<SpawnEvent>) {
                 // NOTE: Will not work if the actor has no engine
                 state.wants_tolookat_id = Some(id.to_string());
             }
+            ["wants", "matchvelocitywith", id] => {
+                // NOTE: Will not work if the actor has no engine
+                state.wants_matchvelocity_id = Some(id.to_string());
+            }
             ["armodel", asset_name] => {
                 state.ar_model = Some(asset_name.to_string());
             }
@@ -617,6 +623,12 @@ fn spawn_entities(
     settings: Res<var::Settings>,
 ) {
     for state_wrapper in er_spawn.read() {
+        let jupiter_pos: DVec3 = if let Some(jupiter_pos) = id2pos.0.get(ID_JUPITER) {
+            *jupiter_pos
+        } else {
+            warn!("Could not determine Jupiter's position");
+            DVec3::ZERO
+        };
         let state = &state_wrapper.0;
         let mut rotation = state.rotation;
         if state.class == DefClass::Actor {
@@ -668,6 +680,13 @@ fn spawn_entities(
                     1.0
                 } * state.model_scale,
             );
+            let orbits_jupiter = state.id != ID_JUPITER;
+            let velocity = if orbits_jupiter {
+                let coords = absolute_pos - jupiter_pos;
+                state.velocity + nature::orbital_velocity(coords, nature::JUPITER_MASS)
+            } else {
+                state.velocity
+            };
 
             // Spawn the actor
             let actor_entity;
@@ -680,6 +699,9 @@ fn spawn_entities(
                     ..default()
                 });
                 actor.insert(SleepingDisabled);
+                if orbits_jupiter {
+                    actor.insert(actor::OrbitsJupiter);
+                }
                 actor.insert(world::DespawnOnPlayerDeath);
                 actor.insert(actor::HitPoints::default());
                 actor.insert(Position::from(absolute_pos));
@@ -715,7 +737,7 @@ fn spawn_entities(
                 // Physics Parameters
                 if state.has_physics {
                     actor.insert(RigidBody::Dynamic);
-                    actor.insert(LinearVelocity(state.velocity));
+                    actor.insert(LinearVelocity(velocity));
                     actor.insert(AngularVelocity(state.angular_momentum));
                     actor.insert(ColliderDensity(state.density));
                     if state.collider_is_mesh {
@@ -799,6 +821,9 @@ fn spawn_entities(
                 if let Some(value) = &state.wants_tolookat_id {
                     actor.insert(actor::WantsToLookAt(value.clone()));
                 }
+                if let Some(value) = &state.wants_matchvelocity_id {
+                    actor.insert(actor::WantsMatchVelocityWith(value.clone()));
+                }
                 if let Some(color) = state.light_color {
                     actor.insert((
                         PointLight {

src/data/defs.txt

@@ -122,11 +122,11 @@ actor 0 0 0
                 only_in_map_at_dist 1e7 amalthea
                 clickable no
                 physics off
-        actor 0 127093 0 moonlet
+        actor 0 0 0 moonlet
             name Thebe
             relativeto jupiter
             id thebe
-            orbit 221900e3 0.34
+            orbitaround jupiter 221900e3
             scale 50e3
             moon yes
             angularmomentum 0 0.025 0
@@ -256,10 +256,11 @@ actor 0 0 0
             physics off
 
 
-actor 0 593051 0 suitv2
+actor 0 59305 0 suitv2
     template person
     relativeto jupiter
-    orbit 221900e3 0.338
+    orbitaround jupiter 221900e3
+    orbit_phase_offset 0.002
     player yes
     id player
     wants maxvelocity none
@@ -287,6 +288,7 @@ actor -55e3 44e3 0 suitv2
     name "Yuni"
     chatid Yuni
     rotationx 180
+    wants matchvelocitywith thebe
 
 actor 5000 0 -3000 moonlet
     name Moonlet
@@ -308,12 +310,14 @@ actor 13200 300 -3000 hollow_asteroid
     actor 0 0 0 suitv2
         template person
         relativeto cultasteroid
+        wants matchvelocitywith cultasteroid
         name "Ash"
         chatid Ash
         pronoun they
     actor -8 8 0 suitv2
         template person
         relativeto cultasteroid
+        wants matchvelocitywith cultasteroid
         name "River"
         chatid River
         rotationy 54
@@ -442,6 +446,7 @@ actor -3300 10 0 pizzeria
         relativeto pizzeria
         armodel clippy_ar
         wants lookat PLAYERCAMERA
+        wants matchvelocitywith pizzeria
         rotationy -126
         chatid SubduedClippy
 
@@ -452,6 +457,7 @@ actor -3300 10 0 pizzeria
         chatid PizzaChef
         armodel suit_ar_chefhat
         wants lookat PLAYERCAMERA
+        wants matchvelocitywith pizzeria
         rotationy -90
         pronoun he
 
@@ -464,6 +470,7 @@ actor 30 -12 -40 suitv2
     armodel suit_ar_wings
     angularmomentum 0.4 0.2 0.1
     wants maxrotation 0.5
+    wants matchvelocitywith pizzeria
     rotationy 108
     rotationx 180
     pronoun it
@@ -495,6 +502,7 @@ actor -300 0 40 suitv2
     name "梓涵"
     chatid Drifter
     alive no
+    wants maxvelocity none
     oxygen 0.08
     pronoun she
 
@@ -505,12 +513,14 @@ actor 100 -18000 2000 clippy
     name "StarTrans Clippy™ Serenity Station"
     armodel clippy_ar
     wants lookat PLAYERCAMERA
+    wants matchvelocitywith orbbusstopserenity
     rotationy -90
     chatid ClippyTransSerenity
 
     actor 60 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Serenity Station"
         relativeto busstopclippy
+        id orbbusstopserenity
         scale 5
     actor 80 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Serenity Station"
@@ -637,6 +647,7 @@ actor 100 -18000 2000 clippy
     actor 8 20 0 suitv2
         template person
         relativeto "busstopclippy"
+        wants matchvelocitywith orbbusstopserenity
         name "Rudy"
         chatid NPCinCryoStasis
         pronoun he
@@ -648,12 +659,14 @@ actor -184971e3 149410e3 -134273e3 clippy
     name "StarTrans Clippy™ Farview Station"
     armodel clippy_ar
     wants lookat PLAYERCAMERA
+    wants matchvelocitywith orbbusstopfarview
     rotationy -90
     chatid ClippyTransFarview
 
     actor 60 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Farview Station"
         relativeto busstopclippy2
+        id orbbusstopfarview
         scale 5
     actor 80 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Farview Station"
@@ -785,6 +798,7 @@ actor 0 -44e3 0 clippy
     name "StarTrans Clippy™ Metis Prime Station"
     armodel clippy_ar
     wants lookat PLAYERCAMERA
+    wants matchvelocitywith orbbusstopmetis
     orbitaround jupiter 128000e3
     orbit_phase_offset -0.002
     rotationy -90
@@ -793,6 +807,7 @@ actor 0 -44e3 0 clippy
     actor 60 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Metis Prime Station"
         relativeto busstopclippy3
+        id orbbusstopmetis
         scale 5
     actor 80 0 0 "orb_busstop"
         name "StarTrans Bus Stop: Metis Prime Station"

src/game.rs

@@ -18,6 +18,10 @@ use bevy::window::{PrimaryWindow, Window, WindowMode};
 use bevy_xpbd_3d::prelude::*;
 use std::collections::HashMap;
 
+pub const CHEAT_WARP_1: &str = "pizzeria";
+pub const CHEAT_WARP_2: &str = "busstopclippy2";
+pub const CHEAT_WARP_3: &str = "busstopclippy3";
+
 pub struct GamePlugin;
 impl Plugin for GamePlugin {
     fn build(&self, app: &mut App) {
@@ -26,12 +30,15 @@ impl Plugin for GamePlugin {
         app.add_systems(PostUpdate, handle_game_event);
         app.add_systems(PreUpdate, handle_player_death);
         app.add_systems(PostUpdate, update_id2pos);
+        app.add_systems(PostUpdate, update_id2v);
         app.add_systems(
             Update,
             handle_achievement_event.run_if(on_event::<AchievementEvent>()),
         );
         app.add_systems(Update, check_achievements);
         app.insert_resource(Id2Pos(HashMap::new()));
+        app.insert_resource(Id2V(HashMap::new()));
+        app.insert_resource(JupiterPos(DVec3::ZERO));
         app.insert_resource(var::AchievementTracker::default());
         app.insert_resource(var::Settings::default());
         app.insert_resource(var::GameVars::default());
@@ -50,6 +57,10 @@ pub struct PlayerDiesEvent(pub actor::DamageType);
 #[derive(Resource)]
 pub struct Id2Pos(pub HashMap<String, DVec3>);
 #[derive(Resource)]
+pub struct Id2V(pub HashMap<String, DVec3>);
+#[derive(Resource)]
+pub struct JupiterPos(pub DVec3);
+#[derive(Resource)]
 pub struct AchievementCheckTimer(pub Timer);
 
 #[derive(Event)]
@@ -260,7 +271,9 @@ fn handle_cheats(
     >,
     mut ew_playerdies: EventWriter<PlayerDiesEvent>,
     mut settings: ResMut<Settings>,
+    jupiter_pos: Res<JupiterPos>,
     id2pos: Res<Id2Pos>,
+    id2v: Res<Id2V>,
     mut ew_sfx: EventWriter<audio::PlaySfxEvent>,
 ) {
     if q_player.is_empty() || q_life.is_empty() {
@@ -285,7 +298,7 @@ fn handle_cheats(
 
     if key_input.just_pressed(settings.key_cheat_stop) {
         gforce.ignore_gforce_seconds = 1.0;
-        v.0 = DVec3::ZERO;
+        v.0 = nature::orbital_velocity(pos.0 - jupiter_pos.0, nature::JUPITER_MASS);
     }
     if key_input.pressed(settings.key_cheat_speed)
         || key_input.pressed(settings.key_cheat_speed_backward)
@@ -319,22 +332,31 @@ fn handle_cheats(
     }
 
     if key_input.just_pressed(settings.key_cheat_pizza) {
-        if let Some(target) = id2pos.0.get(&"pizzeria".to_string()) {
+        if let Some(target) = id2pos.0.get(&CHEAT_WARP_1.to_string()) {
             pos.0 = *target + DVec3::new(-60.0, 0.0, 0.0);
             gforce.ignore_gforce_seconds = 1.0;
         }
+        if let Some(target) = id2v.0.get(&CHEAT_WARP_1.to_string()) {
+            v.0 = *target;
+        }
     }
     if key_input.just_pressed(settings.key_cheat_farview1) {
-        if let Some(target) = id2pos.0.get(&"busstopclippy2".to_string()) {
+        if let Some(target) = id2pos.0.get(&CHEAT_WARP_2.to_string()) {
             pos.0 = *target + DVec3::new(0.0, -1000.0, 0.0);
             gforce.ignore_gforce_seconds = 1.0;
         }
+        if let Some(target) = id2v.0.get(&CHEAT_WARP_2.to_string()) {
+            v.0 = *target;
+        }
     }
     if key_input.just_pressed(settings.key_cheat_farview2) {
-        if let Some(target) = id2pos.0.get(&"busstopclippy3".to_string()) {
+        if let Some(target) = id2pos.0.get(&CHEAT_WARP_3.to_string()) {
             pos.0 = *target + DVec3::new(0.0, -1000.0, 0.0);
             gforce.ignore_gforce_seconds = 1.0;
         }
+        if let Some(target) = id2v.0.get(&CHEAT_WARP_3.to_string()) {
+            v.0 = *target;
+        }
     }
     if key_input.pressed(settings.key_cheat_adrenaline_zero) {
         lifeform.adrenaline = 0.0;
@@ -351,10 +373,24 @@ fn handle_cheats(
     }
 }
 
-fn update_id2pos(mut id2pos: ResMut<Id2Pos>, q_id: Query<(&Position, &actor::Identifier)>) {
+fn update_id2pos(
+    mut id2pos: ResMut<Id2Pos>,
+    mut jupiterpos: ResMut<JupiterPos>,
+    q_id: Query<(&Position, &actor::Identifier)>,
+) {
     id2pos.0.clear();
     for (pos, id) in &q_id {
         id2pos.0.insert(id.0.clone(), pos.0);
+        if id.0 == "jupiter" {
+            jupiterpos.0 = pos.0;
+        }
+    }
+}
+
+fn update_id2v(mut id2v: ResMut<Id2V>, q_id: Query<(&LinearVelocity, &actor::Identifier)>) {
+    id2v.0.clear();
+    for (v, id) in &q_id {
+        id2v.0.insert(id.0.clone(), v.0);
     }
 }
 

src/hud.rs

@@ -707,7 +707,8 @@ fn update_dashboard(
 fn update_speedometer(
     timer: ResMut<FPSUpdateTimer>,
     settings: Res<Settings>,
-    q_camera: Query<&LinearVelocity, With<actor::PlayerCamera>>,
+    jupiter_pos: Res<game::JupiterPos>,
+    q_camera: Query<(&LinearVelocity, &Position), With<actor::PlayerCamera>>,
     q_player: Query<&actor::ExperiencesGForce, With<actor::Player>>,
     q_target: Query<&LinearVelocity, With<IsTargeted>>,
     mut q_speedometer: Query<&mut Style, (With<Speedometer>, Without<Speedometer2>)>,
@@ -717,8 +718,9 @@ fn update_speedometer(
     if !settings.hud_active || !timer.0.just_finished() {
         return;
     }
-    if let Ok(cam_v) = q_camera.get_single() {
+    if let Ok((cam_v, pos)) = q_camera.get_single() {
-        let speed = cam_v.length();
+        let orbital_v = nature::orbital_velocity(pos.0 - jupiter_pos.0, nature::JUPITER_MASS);
+        let speed = (cam_v.0 - orbital_v).length();
 
         let speedometer_split = 5_000.0;
         if let Ok(mut speedometer) = q_speedometer.get_single_mut() {

src/nature.rs

@@ -27,9 +27,11 @@ pub const G: f64 = 6.6743015e-11; // Gravitational constant in Nm²/kg²
 pub const SOL_RADIUS: f64 = 696_300_000.0;
 pub const JUPITER_RADIUS: f64 = 71_492_000.0;
 pub const JUPITER_RING_RADIUS: f64 = 229_000_000.0;
+pub const EARTH_RADIUS: f64 = 6_371_000.0;
 
 pub const SOL_MASS: f64 = 1.9885e30;
 pub const JUPITER_MASS: f64 = 1.8982e27;
+pub const EARTH_MASS: f64 = 5.972168e24;
 
 // Each star's values: (x, y, z, magnitude, color index, distance, name)
 pub const STARS: &[(f32, f32, f32, f32, f32, f32, &str)] = &include!("data/stars.in");
@@ -163,10 +165,38 @@ pub fn inverse_lorentz_factor_custom_c(speed: f64, c: f64) -> f64 {
     (1.0 - (speed.powf(2.0) / c.powf(2.0))).sqrt()
 }
 
+/// Calculates orbit duration in seconds, with given parameters, assuming circular orbit.
 pub fn simple_orbital_period(mass: f64, distance: f64) -> f64 {
     return 2.0 * PI * (distance.powf(3.0) / (G * mass)).sqrt();
 }
 
+/// Calculates the orbital velocity with given parameters, assuming prograde circular orbit.
+pub fn orbital_velocity(coords: DVec3, mass: f64) -> DVec3 {
+    let r = coords.length();
+    let speed = (G * mass / r).sqrt();
+
+    // This generates a perpendicular orbital vector in the prograde direction
+    let perpendicular = DVec3::new(coords.z, 0.0, -coords.x).normalize();
+
+    return perpendicular * speed;
+}
+
+/// Calculates the acceleration towards a mass in m/s
+pub fn gravitational_acceleration(coords: DVec3, mass: f64) -> DVec3 {
+    let r_squared = coords.length_squared();
+    let acceleration_magnitude = G * mass / r_squared;
+    return -acceleration_magnitude * (coords / r_squared.sqrt());
+}
+
+#[test]
+fn test_gravitational_acceleration() {
+    let coords = DVec3::new(EARTH_RADIUS, 0.0, 0.0);
+    let mass = EARTH_MASS;
+    let g = gravitational_acceleration(coords, mass);
+    let g_rounded = (g * 10.0).round() / 10.0;
+    assert_eq!(g_rounded, DVec3::new(-9.8, 0.0, 0.0));
+}
+
 pub fn phase_dist_to_coords(phase_radians: f64, distance: f64) -> DVec3 {
     return DVec3::new(
         distance * phase_radians.cos(),

src/world.rs

@@ -19,6 +19,7 @@ use bevy_xpbd_3d::prelude::*;
 use fastrand;
 use std::collections::HashMap;
 
+const ENABLE_ASTEROIDS: bool = false;
 const ASTEROID_UPDATE_INTERVAL: f32 = 0.1; // seconds
 const ASTEROID_SIZE_FACTOR: f32 = 10.0;
 const RING_THICKNESS: f64 = 8.0e6;
@@ -36,19 +37,21 @@ pub struct WorldPlugin;
 impl Plugin for WorldPlugin {
     fn build(&self, app: &mut App) {
         app.add_systems(Startup, setup);
-        app.add_systems(PostUpdate, handle_despawn);
-        app.add_systems(Update, spawn_despawn_asteroids);
         app.add_systems(Update, handle_respawn.run_if(on_event::<RespawnEvent>()));
         app.add_plugins(PhysicsPlugins::default());
         //app.add_plugins(PhysicsDebugPlugin::default());
         app.insert_resource(Gravity(DVec3::splat(0.0)));
+        app.insert_resource(ActiveAsteroids(HashMap::new()));
+        app.add_event::<RespawnEvent>();
+        if ENABLE_ASTEROIDS {
             app.insert_resource(AsteroidUpdateTimer(Timer::from_seconds(
                 ASTEROID_UPDATE_INTERVAL,
                 TimerMode::Repeating,
             )));
-        app.insert_resource(ActiveAsteroids(HashMap::new()));
+            app.add_systems(Update, spawn_despawn_asteroids);
+            app.add_systems(PostUpdate, handle_despawn_asteroids);
             app.add_event::<DespawnAsteroidEvent>();
-        app.add_event::<RespawnEvent>();
+        }
     }
 }
 
@@ -344,7 +347,7 @@ fn spawn_despawn_asteroids(
     }
 }
 
-fn handle_despawn(
+fn handle_despawn_asteroids(
     mut commands: Commands,
     mut er_despawn: EventReader<DespawnAsteroidEvent>,
     mut db: ResMut<ActiveAsteroids>,