Re: Two arpeggio lines (up and down) next to each other

[Lukas-Fabian Moser]

> > The problem is that this arpeggio is not taken into account for spacing: The 
> > next note will be too close. I'm not yet sure what would be The Right Way to 
> > change this, as neither X-extent nor extra-spacing-width of the arpeggio seem 
> > to have an effect for spacing to the right. You can tweak (for instance) 
> > NoteHead's extra-spacing-width, but that is far from elegant.
> Hmmm… That seems like a bug, or at least a good candidate for a feature 
> request. There are a whole bunch of other ways to clothe that particular cat, 
> but tweaking the width/spacing sure seems like The Right Way™.

Jean Abou Samra knew how to fix that behaviour of arpeggios, so here's a 
(I hope) working solution:

\version "2.22"

Arpeggio_axis_group_engraver =
% Due to Jean Abou Samra
% cf. https://gitlab.com/lilypond/lilypond/-/issues/6193#note_700760004
#(lambda (context)
   (let ((arpeggio #f)
         (note-column #f))
     (make-engraver
      (acknowledgers
       ((arpeggio-interface engraver grob source-engraver)
        (set! arpeggio grob))
       ((note-column-interface engraver grob source-engraver)
        (set! note-column grob)))
      ((process-acknowledged engraver)
       (if (and arpeggio note-column)
           (begin
            (ly:axis-group-interface::add-element note-column arpeggio)
            (set! arpeggio #f)
            (set! note-column #f))))
      ((stop-translation-timestep engraver)
       (set! arpeggio #f)
       (set! note-column #f)))))

\layout {
  \context {
    \Voice
    \consists #Arpeggio_axis_group_engraver
  }
}

arpeggioUpDown = {
  \override Arpeggio.stencil =
  #(lambda (grob)
     (let ((one #f) (two #f) (combined-stencil #f))
       (ly:grob-set-property! grob 'arpeggio-direction UP)
       (set! one (ly:arpeggio::print grob))
       (ly:grob-set-property! grob 'arpeggio-direction DOWN)
       (set! two (ly:arpeggio::print grob))
       (set! combined-stencil
             (ly:stencil-add
              one
              (ly:stencil-translate-axis two 1.25 X)))
       (ly:grob-set-property!
        grob 'X-extent
        (ly:stencil-extent combined-stencil X))
       combined-stencil))
  \override Arpeggio.direction = #RIGHT
}

{
  \once \arpeggioUpDown
  <c' e' g' c''>\arpeggio
  c'
}

Lukas