Draw lines in editor

Hi to all.

I want to draw lines for connect start and end of a block (if, for, etc), like VS2015 or Notepad++. I make a service as TextMarkerService used by ErrorPainter. But in that case, it draw a polygon (similar to a vertical line). I have to draw a vertical line. I've calculated start and end positions of lines, but if I scroll text, lines don't scroll. I think is a problem with calculating position considering actual visual lines.

How can I calculate start and end positions (as Point)?

Thanks a lot.

Andrea