From a85763a0e59339d07d2589197fb2a3985e3f92d0 Mon Sep 17 00:00:00 2001
From: ghostly_zsh <ghostly@e3t.cc>
Date: Fri, 28 Nov 2025 18:05:21 -0600
Subject: [PATCH] feat: orbit prediction

---
 crates/unified/src/client/starguide/orbit.rs | 53 ++++++++++++++++----
 1 file changed, 43 insertions(+), 10 deletions(-)

diff --git a/crates/unified/src/client/starguide/orbit.rs b/crates/unified/src/client/starguide/orbit.rs
index e40da6691c7f6642958b7e951028abccd409ac91..c4a46b77d60707056d30ee6d549d50192ad5cb96 100644
--- a/crates/unified/src/client/starguide/orbit.rs
+++ b/crates/unified/src/client/starguide/orbit.rs
@@ -1,6 +1,8 @@
+use std::{f32::consts::PI, ops::Range};
+
 use bevy::window::WindowResized;
 
-use crate::{ecs::{Me, StarguideCamera, StarguideOrbit, StarguideOrbitImage}, prelude::*};
+use crate::{config::planet::Planet, ecs::{Me, StarguideCamera, StarguideOrbit, StarguideOrbitImage}, prelude::*, world_config::WorldConfigResource};
 use bevy::render::render_resource::Extent3d;
 
 pub fn starguide_orbit_plugin(app: &mut App) {
@@ -12,25 +14,56 @@ fn update_orbits(
     orbit_image: Res<StarguideOrbitImage>,
     mut images: ResMut<Assets<Image>>,
     camera: Single<(&Camera, &GlobalTransform, &Projection), With<StarguideCamera>>,
-    me: Single<&Transform, (With<Me>, Without<StarguideCamera>)>,
+    me: Single<(&Transform, &LinearVelocity), (With<Me>, Without<StarguideCamera>)>,
     orbit: Single<&Transform, (With<StarguideOrbit>, Without<Me>, Without<StarguideCamera>)>,
+    world_config: Res<WorldConfigResource>,
+    planets: Query<(&Mass, &Planet, &Transform)>,
 ) {
     let Some(image) = images.get_mut(&orbit_image.0) else {
         error!("Orbit prediction image not found");
         return
     };
+    let Some(world_config) = &world_config.config else {
+        return;
+    };
     let Projection::Orthographic(ref projection) = camera.2.clone() else { return };
     image.clear(&(Color::BLACK.to_srgba().to_u8_array()));
 
-    let player_pos = me.translation - orbit.translation;
-    let player_pos = Vec3::new(player_pos.x, -player_pos.y, player_pos.z);
-    let player_pos = (player_pos / projection.scale).truncate();
-    let player_pos = player_pos + image.size_f32()/2.0;
-    let player_pos = player_pos.as_uvec2();
+    let mut p_mass = 1.0;
+    let mut p_transform = Transform::default();
+    for (mass, planet, transform) in planets {
+        if planet.name == "Earth" {
+            p_mass = mass.0;
+            p_transform = *transform;
+        }
+    }
+
+    // orbit magic
+    let rel_pos = me.0.translation - p_transform.translation;
+    let u = world_config.world.gravity*p_mass;
+    let h = rel_pos.x*me.1.y - rel_pos.y*me.1.x;
+    let r = rel_pos.length();
+    let a = (u*r) / (2.0*u - r*(me.1.x*me.1.x + me.1.y*me.1.y));
+    let e_x = rel_pos.x/r - (h*me.1.y)/u;
+    let e_y = rel_pos.y/r + (h*me.1.x)/u;
+    let f_x = -2.0*a*e_x;
+    let f_y = -2.0*a*e_y;
+
+    // 200 steps in the revolution
+    for i in 0..400 {
+        let theta = (i as f32) / 200.0 * 2.0*PI;
+        let r = (1.0/2.0) * ((f_x*f_x + f_y*f_y - 4.0*a*a) / (-2.0*a - f_x*theta.cos() - f_y*theta.sin()));
+
+        // convert r to image coords
+        let pos = Vec2::new(r*theta.cos(), r*theta.sin());
+        let pos = pos + p_transform.translation.truncate() - orbit.translation.truncate();
+        let pos = Vec2::new(pos.x, -pos.y);
+        let pos = pos / projection.scale;
+        let pos = pos + image.size_f32()/2.0;
+        let pos = pos.as_uvec2();
 
-    for i in (player_pos.x)..(player_pos.x+100) {
-        if !(i >= image.size().x || player_pos.y >= image.size().y) {
-            image.set_color_at(i, player_pos.y, Color::linear_rgb(1.0, 0.0, 0.0)).unwrap();
+        if !(pos.x >= image.size().x || pos.y >= image.size().y) {
+            image.set_color_at(pos.x, pos.y, Color::linear_rgb(1.0, 0.0, 0.0)).unwrap();
         }
     }
 }