getRotateToAngle(vec, center) {
    let a = Vector2.subtract(this, center);
    let b = Vector2.subtract(vec, center);
    let angle = Vector2.angle(b, a);
    return Number.isNaN(angle) ? 0.0 : angle;
  }
Gets the angles between this vector and another vector around a common center of rotation.

@param {Vector2} vec Another vector.
@param {Vector2} center The center of rotation.
@returns {Number} The angle between this vector and another vector around a center of rotation in radians.