ay}$$
  </p>
    <p>
    The notation above, particularly the definition of the blending function
    \(f\), is also based on the
    C code implementation of X-splines from the 
    <a href="http://mcj.sourceforge.net/">XFig</a>
    drawing program
    (<a href="#smith2001xfig">Smith, 2001</a>).
  </p>
    <h2>
      <a name="x-spline-tangent">4. X-spline tangent functions</a>
    </h2>
    <p>
    In order to generate an offset curve for an X-spline, we need to
    differentiate the function \(C(t)\) to f