thi-ng/umbrella

import type { VecOpVVV } from "./api.js";
import { dot } from "./dot.js";
import { mulN } from "./muln.js";
import { set } from "./set.js";

export const faceForward: VecOpVVV = (out, n, i, nref) => {
    !out && (out = n);
    return dot(nref, i) < 0
        ? out !== n
            ? set(out, n)
            : out
        : mulN(out, n, -1);
};