title: WPF Set the value of a property to a ratio of the value of another property
body: <p>I was wondering if in XAML without touching the view model I could do something like <a href="https://stackoverflow.com/questions/2981705/wpf-dynamic-layout-how-to-enforce-square-proportions-width-equals-height">this</a> or <a href="https://stackoverflow.com/questions/9119032/how-to-bind-a-property-of-one-element-to-a-property-of-another-in-xaml">this</a> except use a ratio of the other property.</p>
  
  <p>I have a button control with 2 ellipses inside and I want the margin of one of the ellipses to vary depending on the height of the other. </p>
  
  <p>So something like: </p>
  
  <pre><code>&lt;Ellipse Margin=.2*"{Binding ElementName=OtherEllipse, Path=Height}"/&gt;
  </code></pre>