Guitar barre

This snippet shows three ways to get barré and half barré chords.

\version "2.24.0"

%% http://lsr.di.unimi.it/LSR/Item?id=952
% added by P.P.Schneider on Sept.2014.
% revised by Harm
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\paper { tagline = ##f }

Prefix = \markup {
  %% uncomment/comment these lines for C, C slashed, B or B slashed prefix :
  \roman C
  %\combine \roman C \translate #'(0.65 . -0.25) \override #'(thickness . 1.2) \draw-line #'(0 . 1.8)
  %\roman B
  %\combine \roman B \translate #'(0.65 . -0.25) \override #'(thickness . 1.2) \draw-line #'(0 . 1.8)
  %%%%%%%%%%%%
  \hspace #0.2
}

#(define-markup-command (prefix layout props string-qty) (integer?)
  (interpret-markup layout props 
    (if (member string-qty (iota 4 2 1))
        #{
           \markup { 
             \override #'(font-family . typewriter)
             \concat {
               \fontsize #-4 {
                   \raise #.5 #(number->string string-qty)
                   \hspace #-.2
                   \raise #.2 "/"
                   \hspace #-.2
                   "6" 
                 }
               \Prefix
             }
           }
        #}
        #{ \markup\Prefix #})))
        
startBarre = 
#(define-event-function (arg-string-qty str) 
  ((integer?) markup?)
  (let* ((pre-fix 
           (if arg-string-qty #{ \markup \prefix #arg-string-qty #} Prefix))
         (mrkp (markup #:upright #:concat (pre-fix str #:hspace 0.3))))
  
     (define (width grob text-string)
       (interval-length
         (ly:stencil-extent
           (grob-interpret-markup grob (markup text-string))
           X)))
    #{  
      \tweak after-line-breaking 
        #(lambda (grob)
          (let* ((mrkp-width (width grob mrkp))
                 (line-thickness (ly:staff-symbol-line-thickness grob)))
           (ly:grob-set-nested-property! 
             grob 
             '(bound-details left padding) 
             (+ (/ mrkp-width -4) (* line-thickness 2)))))     
      \tweak font-size -2
      \tweak style #'line
      \tweak bound-details.left.text #mrkp
      \tweak bound-details.left.attach-dir -1
      \tweak bound-details.left-broken.text ##f
      \tweak bound-details.left-broken.attach-dir -1
      %% adjust the numeric values to fit your needs:
      \tweak bound-details.left-broken.padding 1.5
      \tweak bound-details.right-broken.padding 0
      \tweak bound-details.right.padding 0.25
      \tweak bound-details.right.attach-dir 2
      \tweak bound-details.right-broken.text ##f
      \tweak bound-details.right.text
        \markup
          \with-dimensions #'(0 . 0) #'(-.3 . 0) 
          \draw-line #'(0 . -1)
      \startTextSpan  
    #}))
    
#(define startHalfBarre startBarre)

startModernBarre = 
#(define-event-function (fretnum partial) 
   (number? number?)
    #{
      \tweak bound-details.left.text
        \markup 
          \small \bold \concat { 
          %\Prefix
          #(format #f "~@r" fretnum)
          \hspace #.2
          \lower #.3 \fontsize #-2 #(number->string partial) 
          \hspace #.5
        }
      \tweak font-size -1
      \tweak font-shape #'upright
      \tweak style #'dashed-line
      \tweak dash-fraction #0.3
      \tweak dash-period #1 
      \tweak bound-details.left.stencil-align-dir-y #0.35
      \tweak bound-details.left.padding 0.25
      \tweak bound-details.left.attach-dir -1
      \tweak bound-details.left-broken.text ##f
      \tweak bound-details.left-broken.attach-dir -1
      %% adjust the numeric values to fit your needs:
      \tweak bound-details.left-broken.padding 1.5
      \tweak bound-details.right-broken.padding 0
      \tweak bound-details.right.padding 0.25
      \tweak bound-details.right.attach-dir 2
      \tweak bound-details.right-broken.text ##f
      \tweak bound-details.right.text
        \markup
          \with-dimensions #'(0 . 0) #'(-.3 . 0) 
          \draw-line #'(0 . -1)
      \startTextSpan 
   #})

stopBarre = \stopTextSpan

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXAMPLES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        
%%%%%%%%%%%%%%%%% Standard Barr� function 

%% Syntax: note \startBarre "text"  notes \stopBarre (text = any fret number)

\markup \column \italic { "Standard notation:" \vspace #.5 }

{ 
  \clef "G_8" 
  \key d\minor
  << 
    \new Voice { 
      \voiceOne a'16[ \startBarre "III"  bes d' bes f'8] \stopBarre 
    } 
    \new Voice { \voiceTwo d2 } 
  >>
}

%%%%%%%%%%%%%%%%% Half Barr� function with prefix 

%% Syntax: note \startHalfBarre #'string quantity' "text"  notes \stopBarre (text = any fret number)

\markup 
  \column \italic { \vspace #1 "With string position prefix:" \vspace #.5 }

{ 
  \clef "G_8" 
  \key d\minor
  << 
    \new Voice { 
      \voiceOne a'16[ \startHalfBarre #3 "III" bes d' bes f'8] \stopBarre 
    } 
    \new Voice { \voiceTwo d2 } 
  >>
}

%%%%%%%%%%%%%%%%% Modern Barr� function 

%% Syntax: note \startModernBarre fret-number string-number notes \stopBarre

\markup \column \italic { \vspace #1 "A more modern approach:" \vspace #.5 }
{ 
  \clef "G_8" 
  \key d\minor
  << 
    \new Voice { 
      \voiceOne a'16[ \startModernBarre #3 #3 bes d' bes f'8] \stopBarre 
    } 
    \new Voice { \voiceTwo d2 } 
  >>
}