Jean Abou Samra knew how to fix that behaviour of arpeggios, so here's
a (I hope) working solution:
It seems we can continue this game of "LilyPond experts explain how to
do things and I only have to post the resulting, ever simpler examples"
for some time. :-)
Harm pointed out in
https://gitlab.com/lilypond/lilypond/-/issues/6193#note_701181244 that
it suffices to do:
\version "2.22"
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))
(ly:pointer-group-interface::add-grob
(ly:grob-parent grob X) 'elements grob)
combined-stencil))
\override Arpeggio.direction = #RIGHT
}
{
\once \arpeggioUpDown
<c' e' g' c''>\arpeggio
c'
}
Lukas
