Flute slap notation

It is possible to indicate special articulation techniques such as a flute “tongue slap” by replacing the note head with the appropriate glyph. For that we can draw the accent-like note head with \markup.

\version "2.24"

slap =
#(define-music-function (music) (ly:music?)
  #{
    \temporary \override NoteHead.stencil =
      #ly:text-interface::print
    \temporary \override NoteHead.text =
      \markup
        \translate #'(1 . 0) 
          \override #'(thickness . 1.4) 
            \overlay { \draw-line #'(-1.2 . 0.4)
                       \draw-line #'(-1.2 . -0.4) }
    \temporary \override NoteHead.stem-attachment =
      #(lambda (grob)
        (let* ((stem (ly:grob-object grob 'stem))
               (dir (ly:grob-property stem 'direction UP))
               (is-up (eqv? dir UP)))
          (cons dir (if is-up 0 -0.8))))
    #music
    \revert NoteHead.stencil
    \revert NoteHead.text
    \revert NoteHead.stem-attachment
  #})

\relative c' {
  c4 \slap c d r
  \slap { g4 a } b r
}