From 7e8e500ddfd29d6b7102309becba48aaca52fd74 Mon Sep 17 00:00:00 2001
From: ghostlyzsh <pokeball.181818@gmail.com>
Date: Sun, 26 Nov 2023 20:45:44 -0600
Subject: [PATCH] added gravity

---
 server/src/main.rs | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/server/src/main.rs b/server/src/main.rs
index f2437696f1615b9205464a563f169a6f2028623e..c01e16b8023f465e82e891c4a40ab31b7019d77d 100644
--- a/server/src/main.rs
+++ b/server/src/main.rs
@@ -14,6 +14,7 @@ pub mod macros;
 
 const SCALE: f32 = 10.0;
 const EARTH_SIZE: f32 = 1000.0;
+const GRAVITY: f32 = 0.02;
 
 fn main() {
     let subscriber = tracing_subscriber::FmtSubscriber::new();
@@ -33,10 +34,10 @@ fn main() {
         .add_plugins(RapierPhysicsPlugin::<NoUserData>::pixels_per_meter(SCALE))
         .add_plugins(TwiteServerPlugin)
         .add_systems(Startup, spawn_planets)
-        //.add_systems(Update, on_connection)
         .add_systems(Update, on_message)
         .add_systems(Update, on_close)
         .add_systems(FixedUpdate, on_position_change)
+        .add_systems(FixedUpdate, do_gravity)
         .run();
 
     info!("Goodbye!");
@@ -51,6 +52,8 @@ fn spawn_planets(mut commands: Commands) {
             transform: TransformBundle::from(earth_pos),
         })
         .insert(Collider::ball(EARTH_SIZE / SCALE))
+        .insert(AdditionalMassProperties::Mass(10000.0))
+        .insert(ReadMassProperties::default())
         .insert(RigidBody::Fixed);
 }
 
@@ -91,6 +94,9 @@ fn on_message(
                             player: Player { addr: *addr, username: username.to_string() },
                         })
                         .insert(Collider::cuboid(25.0 / SCALE, 25.0 / SCALE))
+                        .insert(AdditionalMassProperties::Mass(10.0))
+                        .insert(ExternalImpulse { impulse: Vec2::ZERO, torque_impulse: 0. })
+                        .insert(ReadMassProperties::default())
                         .insert(RigidBody::Dynamic)
                         .id().index();
 
@@ -228,3 +234,24 @@ fn on_position_change(
         packet_send.send(ServerEvent::Broadcast(MessageType::Text, buf));
     }
 }
+
+fn do_gravity(
+    mut part_query: Query<(&Transform, &ReadMassProperties, &mut ExternalImpulse), With<PartType>>,
+    planet_query: Query<(&Transform, &ReadMassProperties), With<PlanetType>>,
+) {
+    for (part_transform, part_mp, mut impulses) in &mut part_query {
+        impulses.impulse = Vec2::ZERO;
+        let part_mp = part_mp.get();
+        let part_mass = part_mp.mass;
+        let part_translate = part_transform.translation;
+        for (planet_transform, planet_mp) in &planet_query {
+            let planet_mp = planet_mp.get();
+            let planet_mass = planet_mp.mass;
+            let planet_translate = planet_transform.translation;
+            let distance = planet_translate.distance(part_translate);
+            let force = GRAVITY * ((part_mass * planet_mass) / (distance * distance));
+            let direction = (planet_translate - part_translate).normalize() * force;
+            impulses.impulse += direction.xy();
+        }
+    }
+}