1. Pick a line and endpoint, go there, pen down.
   (you might want to use a heuristic here such as pick the closest point to where you are).
2. go to other endpoint, mark line complete
3. search through list of lines and find a new line with same endpoint.
   (you might want to use a heuristic here to continue going straight if you can).
  if no more lines: end
  else if you found one: goto 2
  else: pen up, goto 1