const calculateNormal = (x, z) => {
    // Find vertex neighbors
    let a = getHeight(x - 1, z).height;
    let b = getHeight(x + 1, z).height;
    let c = getHeight(x, z - 1).height;
    let d = getHeight(x, z + 1).height;

    // Compute the cross product
    let u = a - b;
    let v = 2;
    let w = c - d;

    // Normalize
    let m = Math.sqrt(u * u + v * v + w * w);
    u /= m;
    v /= m;
    w /= m;

    return [u, v, w];
};