@woosh/meep-engine/src/core/geom/3d/shape/UnitSphereShape3D.js

Pure JavaScript game engine. Fully featured and production ready.

import { randomPointInSphere } from "../../random/randomPointInSphere.js";
import { v3_length } from "../../vec3/v3_length.js";
import { AbstractShape3D } from "./AbstractShape3D.js";
import { compute_signed_distance_gradient_by_sampling } from "./util/compute_signed_distance_gradient_by_sampling.js";

/**
 * Sphere with diameter of 2 (radius = 1)
 */
export class UnitSphereShape3D extends AbstractShape3D {
    get volume() {
        return (4 / 3) * Math.PI;
    }

    get surface_area() {
        return Math.PI * 4;
    }

    support(result, result_offset, direction_x, direction_y, direction_z) {

        // since the sphere has a radius of 1, we don't have to multiply by it

        result[result_offset] = direction_x;
        result[result_offset + 1] = direction_y;
        result[result_offset + 2] = direction_z;

    }

    compute_bounding_box(result) {
        result[0] = -1;
        result[1] = -1;
        result[2] = -1;

        result[3] = 1;
        result[4] = 1;
        result[5] = 1;
    }

    nearest_point_on_surface(result, reference) {

        const r_x = reference[0];
        const r_y = reference[1];
        const r_z = reference[2];

        // normalize vector to 1 radius
        const d = 1 / v3_length(r_x, r_y, r_z);

        result[0] = r_x * d;
        result[1] = r_y * d;
        result[2] = r_z * d;
    }

    signed_distance_gradient_at_point(result, point) {
        return compute_signed_distance_gradient_by_sampling(result, this, point);
    }

    signed_distance_at_point(point) {
        return v3_length(
            point[0],
            point[1],
            point[2]
        ) - 1;
    }

    contains_point(point) {
        const x = point[0];
        const y = point[1];
        const z = point[2];

        return (x * x + y * y + z * z) < 1;
    }

    sample_random_point_in_volume(result, result_offset, random) {
        randomPointInSphere(random, result, result_offset);
    }

    hash() {
        return 13;
    }
}

UnitSphereShape3D.INSTANCE = new UnitSphereShape3D();