~starkingdoms/starkingdoms

ref: 3baefd267c9dd87161eff147d93a47e136616c14 starkingdoms/server/src/orbit/orbit.rs -rw-r--r-- 2.1 KiB
3baefd26 — core Merge remote-tracking branch 'origin/master' 2 years ago 
                                                                                
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// Mostly stolen from SebLague's plane game
// thanks

use log::debug;
use nalgebra::{vector, Vector2};
use crate::orbit::newtonian::solve_kepler_with_newtonian;
use crate::orbit::vis_viva::vis_viva;
use crate::planet::GRAVITY;

pub fn calculate_vector_of_orbit(periapsis: f64, apoapsis: f64, t: f64, current_x: f64, current_y: f64, orbiting_x: f64, orbiting_y: f64, mass: f64, step: f64) -> Vector2<f64> {
    let semi_major_length = (apoapsis + periapsis) / 2.0;
    let linear_eccentricity = semi_major_length - periapsis; // distance between center and focus

    let target = calculate_world_position_of_orbit(calculate_point_on_orbit(periapsis, apoapsis, t), vector![orbiting_x, orbiting_y]);
    let target_x = target[0];
    let target_y = target[1];

    let delta_x = target_x - current_x;
    let delta_y = target_y - current_y;

    let velocity_x = delta_x / step;
    let velocity_y = delta_y / step;

    let accel_x = velocity_x / step;
    let accel_y = velocity_y / step;

    let fx = accel_x * mass;
    let fy = accel_y * mass;

    vector![fx, fy]
}

pub fn calculate_point_on_orbit(periapsis: f64, apoapsis: f64, t: f64) -> Vector2<f64> {
    let semi_major_length = (apoapsis + periapsis) / 2.0;
    let linear_eccentricity = semi_major_length - periapsis; // distance between center and focus
    let eccentricity = linear_eccentricity / semi_major_length; // 0: circle. 1: parabola. in between: ellipse
    let semi_minor_length = (semi_major_length * semi_major_length - linear_eccentricity * linear_eccentricity).sqrt();

    let mean_anomaly = t * std::f64::consts::PI * 2.0;
    let eccentric_anomaly = solve_kepler_with_newtonian(mean_anomaly, eccentricity, 100);

    let ellipse_center_x = -linear_eccentricity;
    let point_x = eccentric_anomaly.cos() * semi_major_length + ellipse_center_x;
    let point_y = eccentric_anomaly.sin() * semi_minor_length;

    vector![point_x, point_y]
}

pub fn calculate_world_position_of_orbit(point: Vector2<f64>, orbiting_on: Vector2<f64>) -> Vector2<f64> {
    // i have no idea if this is actually right or not
    // we'll find out
    vector![point[0] + orbiting_on[0], point[1] + orbiting_on[1]]
}