title: get data point when user click a line graph using DataVisualization.Charting.Chart
body: <p>I am using DataVisualization.Charting.Chart (winform), I need to get the data point index when user clicks on a line graph in MouseDown event.</p>
  
  <p>I know there is a HitTest function accepting x &amp; y, but for a line graph, we only need to verify x, if we scan the y (0 to height of graph), it will work, but the performance is too bad.</p>