#442 workaround (keeping piano staves alive together)

[Valentin Villenave]

2008/12/17 Valentin Villenave <address@hidden>:
Hi everyone,

Several months ago I posted a (hackish) workaround for #442:
http://lists.gnu.org/archive/html/lilypond-user/2008-12/msg00456.html

%%%

\layout {
  \context { \RemoveEmptyStaffContext }
  \context {
    \name PseudoVoice
    \alias Voice
    \type Engraver_group
    \consists Note_heads_engraver
    \consists Pitch_squash_engraver
    squashedPosition = #0
    \override NoteHead #'stencil = #empty-stencil
  }
  \context {
    \Staff
    \accepts PseudoVoice
    \remove Time_signature_engraver
  }
}


#(define (remove music) ; throw everything into the Big Void...
 (context-spec-music music 'Devnull))

#(define (unpitch music)
  ; in addition to the PitchSquash thing, we need to make
  ; accidentals disappear (since these are engraved at a
  ; Staff level, and since we don't want to affect the
  ; real Voice).
  (let* ((es (ly:music-property music 'elements))
         (e (ly:music-property music 'element))
         (p (ly:music-property music 'pitch)))
    (if (pair? es)
        (ly:music-set-property!
         music 'elements
         (map (lambda (x) (unpitch x)) es)))
    (if (ly:music? e)
        (ly:music-set-property!
         music 'element
         (unpitch e)))
    (if (ly:pitch? p)
          (ly:music-set-property! music 'pitch 0)))
   music)

#(define (event-filter event)
 (let ((n (ly:music-property event 'name)))
  (if (or
    (eq? n 'ContextSpeccedMusic) ; to avoid clefs and ottavas
    (eq? n 'ContextChange) ; cross-staff voices are supported
    (eq? n 'ArpeggioEvent)) ; arpeggios need to go too
    (music-map remove event))
  (if (eq? n 'SimultaneousMusic) ; we don't want a new Voice to be created
    (ly:music-set-property! event 'name 'NoteEvent))))

makeGhost =
#(define-music-function (parser location music) (ly:music?)
 (context-spec-music (music-filter event-filter (unpitch music)) 'PseudoVoice))

PianoFunction=
#(define-music-function (parser location right left) (ly:music? ly:music?)
#{
  \new PianoStaff <<
    \new Staff = "md"
    <<
     \new Voice { \clef treble $right }
     \new Voice { \makeGhost $left }
    >>
    \new Staff = "mg"
    <<
     \new Voice { \clef bass $left }
     \new Voice { \makeGhost $right }
    >>
  >>
#})

\PianoFunction
\relative { c1 \break c \break R \break R \break c }
\relative { c1 R R c c }

%%%%%%%%%%

It works generally well (even supports cross-staff voices, slurs etc)
but I haven't added it to the LSR because it generates a lot of
warnings (for every note, that is):

   Warning: rhythmic head is not part of a rhythmic column

I wonder if it is possible to get rid of these warnings and make it
look less ugly... or is Joe's recent work likely to make a cleaner
implementation possible?


Regards,
Valentin