\path and \postscript in staff

[Helge Kruse]

The appendix A.10.3 of the Lilypond notation manual describes several
possibilities to use \path or \postscript in a \markup context. So you
can use this to draw some lines:

\version "2.18.2"

<<
  \relative c' {
    e4^\markup { \path #0.25 #'((rmoveto 0 0)

                                (rlineto 5 -1)
                                (closepath)) }

    c'_\markup { \path #0.1 #'((rmoveto 0 0)
                              (rlineto 10 1)
                              (closepath)
                              ) }
  }

  \relative c' {
    g8 g g g
  }
>>

But these lines are outside the staff. If you change "(rlineto 10 1)" to
"(rlineto 10 10)" then the starting point is moved down to keep the
markup outside the stuff. Further it doesn't support the x-position of
the next/previous note column.

How can I draw lines from note head to next note head with \path or
\postscript inside the staff? This should be robust to changes in the
other staves, e.g. if the other staff changes to 32th notes.

Regards
Helge