String number extender lines
Make an extender line for string number indications, showing that a
series of notes is supposed to be played all on the same string.
stringNumberSpanner =
#(define-music-function (StringNumber) (string?)
#{
\override TextSpanner.style = #'solid
\override TextSpanner.font-size = #-5
\override TextSpanner.bound-details.left.stencil-align-dir-y = #CENTER
\override TextSpanner.bound-details.left.text =
\markup { \circle \number $StringNumber }
#})
\relative c {
\clef "treble_8"
\stringNumberSpanner "5"
\textSpannerDown
a8\startTextSpan
b c d e f\stopTextSpan
\stringNumberSpanner "4"
g\startTextSpan a
bes4 a g2\stopTextSpan
}