\version "2.12.2"

\paper {
  indent = 0
  ragged-right = ##f
}

#(define (glissando::calc-tab-extra-dy grob)
   (let* ((original (ly:grob-original grob))
          (left-bound (ly:spanner-bound original LEFT))
          (right-bound (ly:spanner-bound original RIGHT))
          (left-pitch (ly:event-property (event-cause left-bound) 'pitch))
          (right-pitch (ly:event-property (event-cause right-bound) 'pitch))
          (left-staff-position (ly:grob-property left-bound 'staff-position))
          (right-staff-position (ly:grob-property right-bound 'staff-position)))

     (if (and (= left-staff-position right-staff-position)
              (< (ly:pitch-semitones right-pitch) (ly:pitch-semitones left-pitch)))
         -0.75
         0.75)))

#(define (extra-dy-test-a grob)
   (let* ((original (ly:grob-original grob))
          (left-bound (ly:spanner-bound original LEFT))
          (right-bound (ly:spanner-bound original RIGHT))
          (left-pitch (ly:event-property (event-cause left-bound) 'pitch))
          (right-pitch (ly:event-property (event-cause right-bound) 'pitch))
          (left-staff-position (ly:grob-property left-bound 'staff-position))
          (right-staff-position (ly:grob-property right-bound 'staff-position)))
     
     (if (= left-staff-position right-staff-position)
         (if (< (ly:pitch-semitones right-pitch) (ly:pitch-semitones left-pitch))
             -0.75
             0.75)

         ;; not on same staff-position -> no extra-dy
         0)))

#(define (extra-dy-test-b grob)
   (let* ((original (ly:grob-original grob))
          (left-bound (ly:spanner-bound original LEFT))
          (right-bound (ly:spanner-bound original RIGHT))
          (left-pitch (ly:event-property (event-cause left-bound) 'pitch))
          (right-pitch (ly:event-property (event-cause right-bound) 'pitch))
          (left-staff-position (ly:grob-property left-bound 'staff-position))
          (right-staff-position (ly:grob-property right-bound 'staff-position)))
     
     ;; apply extra-dy for all glissandos
     (if
      (< (ly:pitch-semitones right-pitch) (ly:pitch-semitones left-pitch))
      -0.75
      0.75)))

tabs = \relative c {
  \set TabStaff.minimumFret = #2
  c'4 \glissando d \glissando e, \glissando f
  \bar "|."
}

\score {
  <<
    \new TabStaff {
      \clef "tab"
      \override Glissando #'extra-dy = #glissando::calc-tab-extra-dy
      \tabs
    }
    \new TabStaff {
      \clef "tab"
      \override Glissando #'extra-dy = #extra-dy-test-a
      \tabs
    }
    \new TabStaff {
      \clef "tab"
      \override Glissando #'extra-dy = #extra-dy-test-b
      \tabs
  }
  >>
}