Re: Pianostaff 4-part writing and rests

[Kieren MacMillan]

Hi Michael,

> There were many 8th notes alternating with 8th rests
> (which should be merged by Lilypond, but can't be automatically)

Did you try the merge-rests-on-positioning trick?

\version "2.19.15"

#(define (rest-score r)
  (let ((score 0)
        (yoff (ly:grob-property-data r 'Y-offset))
        (sp (ly:grob-property-data r 'staff-position)))
    (if (number? yoff)
        (set! score (+ score 2))
        (if (eq? yoff 'calculation-in-progress)
            (set! score (- score 3))))
    (and (number? sp)
         (<= 0 2 sp)
         (set! score (+ score 2))
         (set! score (- score (abs (- 1 sp)))))
    score))

#(define (merge-rests-on-positioning grob)
  (let* ((can-merge #f)
         (elts (ly:grob-object grob 'elements))
         (num-elts (and (ly:grob-array? elts)
                        (ly:grob-array-length elts)))
         (two-voice? (= num-elts 2)))
    (if two-voice?
        (let* ((v1-grob (ly:grob-array-ref elts 0))
               (v2-grob (ly:grob-array-ref elts 1))
               (v1-rest (ly:grob-object v1-grob 'rest))
               (v2-rest (ly:grob-object v2-grob 'rest)))
          (and
           (ly:grob? v1-rest)
           (ly:grob? v2-rest)              
           (let* ((v1-duration-log (ly:grob-property v1-rest 'duration-log))
                  (v2-duration-log (ly:grob-property v2-rest 'duration-log))
                  (v1-dot (ly:grob-object v1-rest 'dot))
                  (v2-dot (ly:grob-object v2-rest 'dot))
                  (v1-dot-count (and (ly:grob? v1-dot)
                                     (ly:grob-property v1-dot 'dot-count -1)))
                  (v2-dot-count (and (ly:grob? v2-dot)
                                     (ly:grob-property v2-dot 'dot-count -1))))
             (set! can-merge
                   (and 
                    (number? v1-duration-log)
                    (number? v2-duration-log)
                    (= v1-duration-log v2-duration-log)
                    (eq? v1-dot-count v2-dot-count)))
             (if can-merge
                 ;; keep the rest that looks best:
                 (let* ((keep-v1? (>= (rest-score v1-rest)
                                      (rest-score v2-rest)))
                        (rest-to-keep (if keep-v1? v1-rest v2-rest))
                        (dot-to-kill (if keep-v1? v2-dot v1-dot)))
                   ;; uncomment if you're curious of which rest was chosen:
                   ;;(ly:grob-set-property! v1-rest 'color green)
                   ;;(ly:grob-set-property! v2-rest 'color blue)
                   (ly:grob-suicide! (if keep-v1? v2-rest v1-rest))
                   (if (ly:grob? dot-to-kill)
                       (ly:grob-suicide! dot-to-kill))
                   (ly:grob-set-property! rest-to-keep 'direction 0)
                   (ly:rest::y-offset-callback rest-to-keep)))))))
    (if can-merge
        #t
        (ly:rest-collision::calc-positioning-done grob))))

alternating_A = {
  c''8 r d'' r e'' r d'' r c''1
}
alternating_B = \transpose c'' c' \alternating_A

\score {  
  \new Staff \with { \override RestCollision.positioning-done = 
#merge-rests-on-positioning } <<
    << { \voiceOne \alternating_A } \\ \new Voice { \voiceTwo \alternating_B } 
>>
  >>
}

\score {  
  \new Staff \with { \override RestCollision.positioning-done = 
#merge-rests-on-positioning } <<
    \transpose c'' d'' << { \voiceOne \alternating_A } \\ \new Voice { 
\voiceTwo \alternating_B } >>
  >>
}

Hope this helps!
Kieren.
_______________________

Kieren MacMillan, composer
www:  <http://www.kierenmacmillan.info>
email:  address@hidden