@woosh/meep-engine/src/core/geom/vec3/v3_angle_cos_between.js

Pure JavaScript game engine. Fully featured and production ready.

import { clamp } from "../../math/clamp.js";
import { v3_dot } from "./v3_dot.js";
import { v3_length } from "./v3_length.js";

/**
 *
 * @param {number} x0
 * @param {number} y0
 * @param {number} z0
 * @param {number} x1
 * @param {number} y1
 * @param {number} z1
 * @returns {number} value between -1 and 1, cosine of the angle between vectors
 */
export function v3_angle_cos_between(
    x0, y0, z0,
    x1, y1, z1
) {

    const d = v3_dot(x0, y0, z0, x1, y1, z1);

    const magnitude_0 = v3_length(x0, y0, z0);
    const magnitude_1 = v3_length(x1, y1, z1);

    const l = magnitude_0 * magnitude_1;

    if (l === 0) {
        // collective magnitude is 0, provide arbitrary angle
        // avoid division by 0
        return 0;
    }

    return clamp(d / l, -1, 1);

}