Re: Automatic Clef Change

[Jean Abou Samra]

Le 05/01/2022 à 07:51, Calvin Ransom a écrit :
> Hi everyone,
> I want to avoid excessive ledger lines in my score and have LilyPond 
> change the clef automatically.
> I am creating a computer generated piece with LilyPond that covers the 
> entire pitch gamut.
> \autochange does not work for this application because it can only use 
> two clefs and it uses two staves. I would like to use the treble, bass 
> and the octave transposition bass and treble clefs.
> Does anyone have a pre-existing function for this or for something 
> similar?
> Regards,


It is relatively straightforward to implement
this in its basic principle, but much less
straightforward to define an algorithm to choose
the clef at each point. Here is a toy implementation.
It computes the set of clefs that make all notes
printed without ledgers (or on the first ledger)
and picks one by preference order: treble, bass,
treble^8, bass_8. If this is too simple and you
need better heuristics, it would be helpful if you
showed the piece or an excerpt so we get an idea.


\version "2.22.1"

#(use-modules (ice-9 match)
              (scm display-lily))

#(define (pitch<=? a b)
   (or (ly:pitch<? a b)
       (equal? a b)))

%% Maps clef names to the range of pitches
%% that can be used with them.  Ordered by
%% preference, earlier entries are picked first
%% if possible.
#(define clef-range-alist
   `(("treble" . (,#{ c' #} . ,#{ a'' #}))
     ("bass" . (,#{ e, #} . ,#{ c' #}))
     ("treble^8" . (,#{ c'' #} . ,#{ a''' #}))
     ("bass_8" . (,#{ e,, #} . ,#{ c #}))))

#(define (allowable-clefs pitch)
   (filter-map
    (match-lambda
      ((clef . (min-pitch . max-pitch))
         (and (pitch<=? min-pitch pitch)
              (pitch<=? pitch max-pitch)
              clef)))
    clef-range-alist))

#(define allowable-clef-names (map car clef-range-alist))

#(define (apply-clef! context clef-input)
   (let* ((clef-set (clef clef-input))
          (sequential (ly:music-property clef-set 'element))
          (elements (ly:music-property sequential 'elements)))
     (for-each
      (lambda (elt)
        (with-music-match
         (elt (music 'PropertySet value ?value symbol ?symbol))
         (ly:context-set-property! context ?symbol ?value))
        (with-music-match
         (elt (music 'ApplyContext procedure ?procedure))
         (?procedure context)))
      elements)))


#(define (Auto_clef_engraver context)
   (let ((allowable allowable-clef-names)
         (previous-clef #f))
     (make-engraver
       (listeners
         ((note-event engraver event)
            (let* ((pitch (ly:event-property event 'pitch)))
              (set! allowable
                    (lset-intersection eq? allowable (allowable-clefs 
pitch)))
              (apply-clef! context
                           (if (null? allowable)
                               (begin
                                 (ly:event-warning event
                                                   "No clef keeping all 
notes in range found")
                                 "treble")
                               (car allowable))))))
       ((stop-translation-timestep engraver)
          (set! allowable allowable-clef-names)))))

\layout {
  \context {
    \Staff
    \consists #Auto_clef_engraver
  }
}

\relative {
  e,, f g a b c d e f g a b c d e f g a b
  c d e f g a b c d e f g a b c d e f g a
}

{
  <c' c''>1
  <c'' c'''>
  <g c'>
  <e, c'>
  <c, c>
}


Best,
Jean