title: Use Gradient with Paint object in Flutter Canvas
body: <p>I am able to draw a semi circle using the following example:
  <a href="https://stackoverflow.com/questions/57748469/flutter-how-to-draw-semicircle-half-circle">Flutter how to draw semicircle (half circle)</a></p>
  
  <p>However, the <code>Paint</code> object only seems to accept a <code>Color</code> (using <code>Paint.color</code>). I would like to add a <code>RadialGradient</code> or <code>LinearGradient</code> as the <code>Color</code>. Is that possible?</p>