title: Draw a vertical line on Left Click MouseDownEvent
body: <p>I'm using the Oxyplot library to plot some graphs based on real-time data. I know there is a feature called <code>Tracker</code> that shows some tooltip-like information (coordinates, for example) based on the <code>Position</code> where the user left-clicks. The information is only shown while the left-button is pressed.</p>
  
  <p>I'm currently testing this functionality on a line graph, not sure if it works for other types.</p>
  
  <p>What I wanted to do is to keep this info on screen and making it disapper only if the user tries to set a new one, clicking somewhere else on the graph and replacing the older information. Adding a vertical bar where the user clicked would be nice too.</p>
  
  <p>I checked the Oxyplot documentation and I know that it is possible to customize this 'Tracker', but I failed to find a solution for my situation.</p>
  
  <p>EDIT:</p>
  
  <p>I've found <a href="https://github.com/oxyplot/oxyplot/blob/develop/Source/Examples/ExampleLibrary/Examples/MouseEventExamples.cs" rel="nofollow">this</a> example, it seems helpful, but I'm struggling to extract the usefulness of it. Please help!</p>
  
  <p>UPDATE:</p>
  
  <p>Let me go a little further on the explanation of what I'm trying to achieve. I have many graphs, each of them placed on a separated panel (or tab). If I left-click in a position of a graph, I want to show the <code>Tracker</code> info on that specific position <strong>on each and every graph</strong> while the user doesn't click on another position (setting a new <code>Tracker</code> and removing the old one). In other words, it is allowed one <code>Tracker</code> at a time, and this is set on every existing graph at the same X-position.</p>
  
  <p>UPDATE 2:</p>
  
  <p>Alright, so after giving it a thought, I decided not to maintain the <code>Tracker</code> when left-clicking. Instead, I just want <strong>to draw a vertical line on every graph on the position of the click</strong>. Just one line at a time is permitted, it can be treated as a "temporary marker". I believe this is more doable than the other approach and will suffice my needs.</p>