title: WPF overlay across multiple windows
body: <p>I have a WPF application using multiple independent windows. I would like to draw a line from one of the windows to another one. This needs to be controlled programmatically and if one of the windows is moved, this line needs to be updated accordingly. </p>
  
  <p>What's the best way to do something like this? A transparent window on top of all others?</p>