@woosh/meep-engine/src/core/geom/3d/sphere/sphere_intersects_ray.js

Pure JavaScript game engine. Fully featured and production ready.

//

import { v3_dot } from "../../vec3/v3_dot.js";

/**
 *
 * @param {number} center_x
 * @param {number} center_y
 * @param {number} center_z
 * @param {number} radius
 * @param {number} origin_x
 * @param {number} origin_y
 * @param {number} origin_z
 * @param {number} direction_x
 * @param {number} direction_y
 * @param {number} direction_z
 * @returns {boolean}
 */
export function sphere_intersects_ray(
    center_x, center_y, center_z, radius,
    origin_x, origin_y, origin_z,
    direction_x, direction_y, direction_z
) {
    const delta_x = center_x - origin_x;
    const delta_y = center_y - origin_y;
    const delta_z = center_z - origin_z;

    const tca = v3_dot(delta_x, delta_y, delta_z, direction_x, direction_y, direction_z);
    const d2 = v3_dot(delta_x, delta_y, delta_z, delta_x, delta_y, delta_z) - tca * tca;

    const radius2 = radius * radius;

    if (d2 > radius2) {
        return false;
    }

    const thc = Math.sqrt(radius2 - d2);

    // t0 = first intersect point - entrance on front of sphere
    const t0 = tca - thc;

    // t1 = second intersect point - exit point on back of sphere
    const t1 = tca + thc;

    // test to see if both t0 and t1 are behind the ray - if so, no intersection
    if (t0 < 0 && t1 < 0) {
        return false;
    }

    return true;
}