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Re: Dashed Stem

From: Thomas Morley
Subject: Re: Dashed Stem
Date: Sat, 12 May 2012 04:24:05 +0200

2012/5/12 David Nalesnik <address@hidden>:

> Looking at this some more, I've come up with an alternate which more closely
> duplicates an ordinary stem.  Instead of using line segments, I used
> round-filled-box stencils, which is what Lily uses to draw stems.
> Everything is fine when the dashes aren't too small.  If you ask for more
> than 6 at staff-size 20, though, some dashes won't appear.  You see similar
> behavior if the staff size is reduced.  (To see this, uncomment the line at
> the top of the function.)  I'm not sure what's going on here, if this is a
> limitation of 'round-filled-box, or something I'm doing wrong.

Hi David,

I suggest the code below. It's very close to your own but it seems to
avoid the problems.

\version "2.15.36"

%#(set-global-staff-size 14)

#(define (make-round-filled-box x1 x2 y1 y2 blot-diameter)
     (ly:make-stencil (list 'round-filled-box (- x1) x2 (- y1) y2 blot-diameter)
                      (cons x1 x2)
                      (cons y1 y2)))

#(define ((dashed-stem num) grob)
   (let* ((blot (ly:output-def-lookup (ly:grob-layout grob) 'blot-diameter))
          (stencil (ly:stem::print grob))
          (X-ext (ly:stencil-extent stencil X))
          (thickness (interval-length X-ext))
          (ext (ly:stencil-extent stencil Y))
          (len (interval-length ext))
          (new-stencil empty-stencil)
              (lambda (x) (* (/ len (1- (* 2 num))) x))
              (iota (* 2 num)))))

   (define (helper args)
     (set! new-stencil
        (ly:stencil-add new-stencil
              (make-round-filled-box (/ thickness -2) (/ thickness 2)
                                     (car args) (cadr args) blot)
              (interval-start ext)
     (if (null? (cddr args))
       (helper (cddr args))))

        (if (zero? num)
            (helper factors))))

%---- test

% compare only avoids too much typing :)

compare =
#(define-music-function (parser location music)(ly:music?)
  (let* ((new-music (ly:music-deep-copy music)))
        \override Stem #'stencil = #(dashed-stem 20)
        \revert Stem #'stencil

\relative c' {
        \compare g
        \compare a
        \compare b
        \compare c
        \compare d
        \compare e
        \compare f
        \compare g
        \compare a
        \compare b
        \compare c
        \compare d
        \compare e
        \compare f
        \compare g
        \compare a

\relative c' {
        \compare \transpose c c' <c e g b>32
        \compare \transpose c d' <c e g b>
        \compare \transpose c e' <c e g b>
        \compare \transpose c f' <c e g b>
        \compare \transpose c g' <c e g b>
        \compare \transpose c a' <c e g b>
        \compare \transpose c b' <c e g b>
        \compare \transpose c c'' <c e g b>


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