\version "2.18.2"

beam-stem-height =
#(define-music-function (parser location start-in length-in)(number? number?)
  "Takes a list containing values for:
  - the stem-start in Y-direction
  - the stem-length
  Values can be positive or negative, depending on direction
  but may produce a warning if only one value is negative:
    'warning: weird stem size, check for narrow beams'
  "
  #{
    \override Stem.direction = #(if (positive? length-in) UP DOWN)
    \override Stem.stem-begin-position = #start-in
    \override Stem.length = #(abs length-in)
    \override Beam.after-line-breaking =
    #(lambda (grob)
      (let ((stems (ly:grob-array->list (ly:grob-object grob 'stems))))
        (for-each
          (lambda (stem)
            (ly:stem::calc-stem-begin-position stem)
            (ly:grob-set-property! stem 'length (abs length-in))
            (ly:grob-set-property! stem 'stem-begin-position start-in))
        stems)))
    \override Beam.before-line-breaking =
    #(lambda (grob)
      (let* ((thickness (ly:grob-property grob 'beam-thickness))
             (position (if (positive? length-in)
               (/ (+ start-in (- (abs length-in)
                 thickness))
                 2)
               (/ (- start-in (- (abs length-in)
                 thickness))
                 2))))
        (ly:grob-set-property! grob 'positions (cons position position))))
#})

halve-half-stems =
\override Stem.before-line-breaking =
  #(lambda (grob)
    (let ((new-length (/ (ly:grob-property grob 'length) 2)))
      (if (= 1 (ly:grob-property grob 'duration-log))
        (if (= DOWN (ly:grob-property grob 'direction))
          (and (ly:grob-set-property! grob 'stem-begin-position
                 (- (ly:grob-property grob 'stem-begin-position) new-length))
               (ly:grob-set-property! grob 'length new-length))
          (ly:grob-set-property! grob 'length new-length)))))

GCEA =
\markup {
  \with-dimensions #'(0 . 0.8) #'(0 . 1.0)
  \postscript #"/Arial-Bold findfont
                1.5 scalefont
                setfont -0.3 2.2 moveto
                (A) show -0.3 0.7 moveto
                (E) show -0.3 -0.8 moveto
                (C) show -0.3 -2.3 moveto
                (G) show
                stroke"
}

addStartBar = \markup {
  \hspace #-.8
  \lower #2.2 % 1.95
  \override #'(thickness . 1.5)
  \draw-line #'(0 . 4.4)
  \hspace #.2
  \musicglyph #"clefs.tab"
}

addStartBarNoClef = \markup {
  \hspace #-0.8
  \lower #2.2 % 1.95
  \override #'(thickness . 1.5)
  \draw-line #'(0 . 4.4)
  \hspace #0.0
  \draw-line #'(0 . 0)
}

start-bar-clef = {
  \override TabStaff.Clef.stencil = #(lambda (grob)
    (grob-interpret-markup grob addStartBar))
}


clef-off = {
  %if you fancy tabstaves that are open on the left, switch these comments
  %\override TabStaff.Clef #'stencil = ##f
  \override TabStaff.Clef.stencil = #(lambda (grob)
    (grob-interpret-markup grob addStartBarNoClef))
}