OK, here's how I did it in the end. Is there a better way???
#(define ac:current-key (make-music
'KeyChangeEvent
'tonic
(ly:make-pitch -1 0 0)
'pitch-alist
(list (cons 0 0)
(cons 1 0)
(cons 2 0)
(cons 3 0)
(cons 4 0)
(cons 5 0)
(cons 6 0))))
#(define (ac:up note)
"Given a NoteEvent, replace its pitch with the next one
up in the current scale.
Doesn't cope too well with melodic minors"
(let* ((pitch (ly:music-property note 'pitch))
(notename (ly:pitch-notename pitch))
(new-notename (if (eq? notename 6) 0 (+ 1 notename)))
(alterations (ly:music-property ac:current-key 'pitch-alist))
(new-alteration (cdr (assq new-notename alterations)))
(new-octave (if (eq? new-notename 0) (+ 1 (ly:pitch-octave pitch))
(ly:pitch-octave pitch)))
)
(set!
(ly:music-property note 'pitch)
(ly:make-pitch new-octave new-notename new-alteration))))
(ac:down is analogous to ac:up)
Whenever I see a KeyChangeEvent in the rest of the program I update
ac:current-key.
Is there a better way? Does Lilypond keep track of the current key
signature for me?
--
Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au ERTOS within National ICT Australia
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