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Re: Two Hands "Snake"

From: Andrew Bernard
Subject: Re: Two Hands "Snake"
Date: Mon, 8 Jul 2019 18:50:10 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2

Hi Marcos,

Here is what I use. I hope you may find it useful. The vibrato function modifies the trill spanner.

Picture attached of real use in the piece I engraved (for 7 string guitar, but that's not really relevant).

I do not recall where I got this from, but the author is acknowledged. The example along with the function code gives you lots of inspiration. Highly parameterised.



%\version "2.19.44"

% Author: Mark Witmer

% Sets the next trill spanner to draw a waveform with the provided wevelength
% and amplitudes. The waveform will go from one amplitude to the next in a
% linear fashion.

vibrato =
#(define-music-function (amplitudes wavelength)
   (list? number?)
     \once \override TrillSpanner #'after-line-breaking =
     $(lambda (grob)
        (ly:grob-set-property! grob 'stencil (makevib grob amplitudes wavelength)))

#(define adjustvib #t)

% Creates the postscript for one system of the vibrato marking
#(define (make_ps no-sib? lbound xspan span-so-far amplitude-vector wavelength)
   (if (or (= xspan -inf.0) (= xspan +inf.0))
       (let ((lbound
               ((and (> span-so-far 0) adjustvib)
                (- lbound 18))
               (no-sib? (+ lbound 1))
               (else lbound)))
              (inexact->exact (floor (/ (+ span-so-far xspan) wavelength)))))
          #f "gsave currentpoint translate 0.15 setlinewidth newpath /x ~a def\nx 0.0 moveto\n ~a ~a"
          (let make-curve
            ((current (inexact->exact (floor (/ span-so-far wavelength)))))
             ((= current (vector-length amplitude-vector)) "")
             ((< (vector-ref amplitude-vector current) 0) "")
              (let ((current-ps
                      #f " x ~a add ~a x ~a add ~a x ~a add 0.0 curveto\n/x x ~a add def\n"
                      (exact->inexact (/ wavelength 3))
                      (vector-ref amplitude-vector current)
                      (exact->inexact (* 2 (/ wavelength 3)))
                      (- (vector-ref amplitude-vector current))
                (if (= (+ current 1) last)
                    (format #f "~a~a" current-ps
                      (make-curve (+ 1 current))))))))
          "stroke grestore"))))

% Returns the width of a grob
#(define (grob-width grob)
   (if (or (= (car (ly:grob-property grob 'X-extent)) -inf.0)
           (= (car (ly:grob-property grob 'X-extent)) +inf.0))
       (- (cdr (ly:grob-property grob 'X-extent))
         (car (ly:grob-property grob 'X-extent)))))

% Returns the number of ems already traversed by the grob's siblings in
% previous systems
#(define (width-up-to grob siblings count)
   (if (eq? (car siblings) grob)
       (+ (+ count (width-up-to grob (cdr siblings) count))
         (grob-width (car siblings)))))

% Returns the total width of the individual grobs for each system that make up
% the original grob
#(define (calcfull siblings count)
   (if (eqv? (length siblings) 0)
       (calcfull (cdr siblings) (+ count (grob-width (car siblings))))))

% Fills a vector of length len with linear interpolations between the values
% found in amplitudes
#(define (fill-amplitude-vector! amplitude-vector len current-index amplitudes)
   (if (> (length amplitudes) 1)
       (let ((start-amplitude (car amplitudes))
             (end-amplitude (cadr amplitudes))
             (start-index current-index)
             (end-index (+ current-index
                           (floor (/ (vector-length amplitude-vector)
                                    (- len 1)))))))
         (do ((n current-index (+ 1 n)))
           ((or (> n (+ start-index end-index))
                (>= n (vector-length amplitude-vector))))
           (vector-set! amplitude-vector n
              (+ start-amplitude
                (* (/ (- n start-index) (- end-index start-index))
                  (- end-amplitude start-amplitude))))))
          amplitude-vector len end-index (cdr amplitudes)))))

% Makes the vector of amplitudes for the vibrato marking
#(define (make-amplitude-vector amplitudes total-span wavelength)
   (let* ((current-start 0)
          (len (inexact->exact (floor (/ total-span wavelength))))
          (amplitude-vector (make-vector len)))
     (if (> (length amplitudes) 1)
          amplitude-vector (length amplitudes) 0 amplitudes)
         (vector-fill! amplitude-vector (car amplitudes)))

% Creates a stencil that draws a sine wave for vibrato based on the provided
% amplitudes and wavelength
#(define (makevib grob amplitudes wavelength)
   (let* ((orig (ly:grob-original grob))
          (siblings (if (ly:grob? orig) (ly:spanner-broken-into orig) '()))
          (span (ly:grob-property grob 'X-extent))
          (xbeg (car span))
          (xend (cdr span))
          (xspan (- xend xbeg))
          (total-span (if (eqv? (length siblings) 0) (- xspan 3) (- (calcfull siblings 0) 3)))
          (lbound (if (or (null? siblings) (eq? (car siblings) grob))
                      0 (+ 14 (cdr (assq 'X (ly:grob-property grob 'left-bound-info))))))
          (span-so-far (if (null? siblings) 0
                           (width-up-to grob siblings 0))))
      (list 'embedded-ps
        (make_ps (null? siblings) lbound xspan span-so-far
          (make-amplitude-vector amplitudes total-span wavelength)
      '(0 . 0) '(-0.7 . 0.5))))

vib =
#(define-music-function (sizes)
     \vibrato $sizes #0.7

sVib = \startTrillSpan
eVib = \stopTrillSpan

% Example:

\relative c' {
  \time 4/4
  \key d \major

  \vibrato #'(4 0 4) #1.5 c\startTrillSpan d e d c d e d c\stopTrillSpan

  \vibrato #'(1 6 2 1 3 7 4) #1 c\startTrillSpan d e d c d e d c d e d c d e d c d e d c d e d c d e d c d e d

  c d e d c d e d c d e d c d e d c d e d c d e d c d e d c d e\stopTrillSpan

\paper {
  ragged-right = ##f

\relative c' {
  \vibrato #'(4 .2 0) #1.2 c1\startTrillSpan c\stopTrillSpan



Attachment: vibrato.png
Description: PNG image

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