update

src/main.rs

@@ -1,15 +1,15 @@
 use bevy::{
     core_pipeline::{bloom::Bloom, tonemapping::Tonemapping},
-    log::tracing_subscriber::field::debug,
     math::DVec3,
     prelude::*,
-    window::{WindowMode, WindowResolution},
+    window::WindowMode,
 };
 use bevy_inspector_egui::{bevy_egui::EguiPlugin, quick::WorldInspectorPlugin};
 use bevy_panorbit_camera::{PanOrbitCamera, PanOrbitCameraPlugin};
 
 // Scaling factor to convert AU to game units
-// This makes the solar system larger so objects are visible at minimum camera zoom
+// Neptune is approximately 30.1 astronomical units (AU) from the Sun
+// Point light effective range is about 10 game units, so 10 game units = ~30 AU
 const AU_TO_GAME_UNITS: f64 = 0.3;
 
 // Unit wrapper types - all distances in AU
@@ -160,7 +160,7 @@ fn setup_rendering(mut commands: Commands) {
             ..default()
         }),
         Tonemapping::TonyMcMapface,
-        Transform::from_translation(Vec3::new(2.0, 1.5, 2.0)),
+        Transform::from_translation(Vec3::new(0., 0., 10.0)),
         Bloom::NATURAL,
         PanOrbitCamera {
             pan_sensitivity: 0.0, // Disable panning by setting sensitivity to 0
@@ -233,7 +233,7 @@ fn update_label_positions(
     };
 
     for (mut node, label, mut text) in label_query.iter_mut() {
-        if let Ok((position, name, radius)) = objects_query.get(label.target_entity) {
+        if let Ok((position, name, _radius)) = objects_query.get(label.target_entity) {
             let world_pos = position.0.0 * AU_TO_GAME_UNITS;
 
             if let Ok(screen_pos) = camera.world_to_viewport(camera_transform, world_pos.as_vec3())
@@ -341,6 +341,74 @@ fn setup_solar_system(mut commands: Commands) {
     ));
 }
 
+// High precision constants
+const G_SI: f64 = 6.67430e-11; // Gravitational constant in m³/kg/s² (2018 CODATA value)
+const AU_TO_M: f64 = 149597870691.0; // AU to meters (IAU 2012 definition, exact)
+const DAY_TO_S: f64 = 86400.0; // Day to seconds (exact)
+
+// Pre-calculated G in AU³/kg/day² units for optimization
+// G_AU = G_SI * (day²/s²) / (AU³/m³)
+// G_AU = G_SI * (DAY_TO_S²) / (AU_TO_M³)
+const G_AU: f64 = G_SI * (DAY_TO_S * DAY_TO_S) / (AU_TO_M * AU_TO_M * AU_TO_M);
+
+const STEPS: usize = 100;
+// Time step calculation:
+// FixedUpdate runs at 64fps, 1 game second = 7 days, 100 steps per FixedUpdate
+// DT = (7 days / 64 fps) / 100 steps = 7 / (64 * 100) = 0.00109375 days per step
+const DT: f64 = 7.0 / (64.0 * STEPS as f64); // Time step in days
+
+fn n_body(mut query: Query<(&Mass, &mut Position, &mut Velocity)>) {
+    // Collect all bodies data (mass, position, velocity)
+    let mut bodies: Vec<(f64, DVec3, DVec3)> = query
+        .iter()
+        .map(|(mass, pos, vel)| (mass.0.0, pos.0.0, vel.0.0))
+        .collect();
+
+    // Perform integration steps
+    for _ in 0..STEPS {
+        // Calculate forces for all bodies
+        let mut forces: Vec<DVec3> = vec![DVec3::ZERO; bodies.len()];
+
+        for i in 0..bodies.len() {
+            for j in 0..bodies.len() {
+                if i != j {
+                    let r_vec = bodies[j].1 - bodies[i].1; // Position difference in AU
+                    let r_mag_au = r_vec.length();
+
+                    if r_mag_au > 1e-10 {
+                        // Avoid division by zero
+                        // Calculate force directly in AU/day² units
+                        let force_magnitude =
+                            G_AU * bodies[i].0 * bodies[j].0 / (r_mag_au * r_mag_au);
+                        let acceleration = force_magnitude / bodies[i].0; // F/m = a
+                        let force_vec = r_vec.normalize() * acceleration;
+
+                        forces[i] += force_vec;
+                    }
+                }
+            }
+        }
+
+        // Update velocities and positions using Verlet integration
+        for i in 0..bodies.len() {
+            // Update velocity: v += a * dt
+            bodies[i].2 += forces[i] * DT;
+
+            // Update position: x += v * dt
+            let velocity = bodies[i].2;
+            bodies[i].1 += velocity * DT;
+        }
+    }
+
+    // Write back updated positions and velocities
+    for (i, (_mass, mut pos, mut vel)) in query.iter_mut().enumerate() {
+        if let Some(body) = bodies.get(i) {
+            pos.0.0 = body.1;
+            vel.0.0 = body.2;
+        }
+    }
+}
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins.set(WindowPlugin {
@@ -356,5 +424,6 @@ fn main() {
         .add_plugins(WorldInspectorPlugin::new())
         .add_plugins(SolarRenderingPlugin)
         .add_systems(Startup, setup_solar_system)
+        .add_systems(FixedUpdate, n_body)
         .run();
 }