angleToSigned method

double angleToSigned (Vector3 other, Vector3 normal)

Returns the signed angle between this and other around normal in radians.

Implementation 

double angleToSigned(Vector3 other, Vector3 normal) {
  final double angle = angleTo(other);
  final Vector3 c = cross(other);
  final double d = c.dot(normal);

  return d < 0.0 ? -angle : angle;
}