code: public Vector3f positiveZ(Vector3f dir) {
          float invNorm = 1.0f / (x * x + y * y + z * z + w * w);
          float nx = -x * invNorm;
          float ny = -y * invNorm;
          float nz = -z * invNorm;
          float nw =  w * invNorm;
          float dx = nx + nx;
          float dy = ny + ny;
          float dz = nz + nz;
          dir.x =  nx * dz + nw * dy;
          dir.y =  ny * dz - nw * dx;
          dir.z = -nx * dx - ny * dy + 1.0f;
          return dir;
      }
docs: /* (non-Javadoc)
  @see org.joml.Quaternionfc#positiveZ(org.joml.Vector3f)