title: Draw a quadratic Bézier curve through three given points
body: <p>I have three points in 2D and I want to draw a quadratic Bézier curve passing through them. How do I calculate the middle control point (<code>x1</code> and <code>y1</code> as in quadTo)? I know linear algebra from college but need some simple help on this. </p>
  
  <p>How can I calculate the middle control point so that the curve passes through it as well?</p>