title: Creating a custom-shaped button with one rounded corner
body: <p>I need to create a button in WPF that has a custom shape. Specifically, I want it to have rounded corners, like an ellipse. Here is a picture:</p>
  <p><img src="https://i.stack.imgur.com/HGxjW.png" alt="" /></p>
  <p>Only the black area should be a click target; the white area should be transparent.</p>
  <p>How would I go about creating a button control in WPF that has such a custom shape? I know how to create a regular rectangular button, but not one with a rounded corner like this.</p>