Re: test spanner with controlled gradient / dynamic volume curve indicated by grey level

[Thomas Morley]

2018-01-31 0:00 GMT+01:00 Michael Winter <address@hidden>:
> That is really beautiful. Thank you. I have been giving myself a crash
> course in scheme and was also getting somewhat closer to a solution using a
> glissando event. Then the internet went down. And low and behold it woke up
> to your response.
>
> So this is almost what I want. And I need to dissect your code a bit more
> (again, still wrapping my head around scheme). Maybe I can adapt it. My
> ultimate goal is to specify the gradient within the given note length (as
> opposed to giving a new color directive for every note. This is where it
> gets tricky. In my current attempt (drowning in the deep end), it is a bit
> tricky because you cannot change colors in the middle of a path directive.
> So you need to combine several markups (as in my original example). I was
> piecing together stuff I found on LSR and in the user archive and was also
> having a huge problem with alignment. My current code is pasted below. It is
> a mess, but getting there. I just was reading about returning markup
> definitions in hopes that I could iterate through the gradient and build the
> markup that way.
>
> En fin, I will study your code. Like I said, it is almost exactly what I
> want except I want the gradient within the note length. Of course, any help
> in that direction will be much appreciated.
>
> Best,
>
> Michael

How about below then:

\version "2.19.65"

\paper { ragged-right = ##f }

\layout {
  \context {
      \Staff
      \override StaffSymbol.line-count = #1
  }
  \context {
      \Voice
      \override Glissando.minimum-length = #0
      %% n.b. line-breaks are TODO
      \override Glissando.breakable = ##t
      \override Glissando.after-line-breaking = ##t
      \override Glissando.bound-details =
        #'((right
             (attach-dir . 0)
             (end-on-accidental . #f)
             (padding . 0.))
           (left
             (attach-dir . 0)
             (padding . 0.)))
    }
}

#(define (make-grey-filled-box-stencil-list x-coords color-steps half-thick rl)
  (if (null? (cdr x-coords))
      rl
      (make-grey-filled-box-stencil-list
        (cdr x-coords)
        (cdr color-steps)
        half-thick
        (cons
          (stencil-with-color
            (make-filled-box-stencil
              (interval-widen (cons (car x-coords) (cadr x-coords)) 0.1)
              (cons (- half-thick) half-thick))
            (x11-color
              (string->symbol (format #f "grey~a" (car color-steps)))))
          rl))))

#(define my-gliss
  (lambda (grob)
    (if (ly:stencil? (ly:line-spanner::print grob))
        (let* ((left-bound-info (ly:grob-property grob 'left-bound-info))
               (left-Y (assoc-get 'Y left-bound-info))
               (left-X (assoc-get 'X left-bound-info))
               (right-bound-info (ly:grob-property grob 'right-bound-info))
               (right-X (assoc-get 'X right-bound-info))
               (thick (ly:grob-property grob 'thickness 0.5))
               (delta-X (- right-X left-X))
               (steps
                 (assoc-get 'color-steps (ly:grob-property grob 'details) 100))
               (raw-color-steps
                 (iota (abs steps) 0 (round (/ 100 (min 100 (abs steps))))))
               (color-steps
                 (if (negative? steps)
                     (reverse raw-color-steps)
                     raw-color-steps))
               (x-coords (iota (1+ (abs steps)) 0 (/ delta-X (abs steps)))))

          ;; create a flat glissando
          (ly:grob-set-nested-property! grob '(right-bound-info Y) left-Y)

          ;; return the stencil of added boxes
          (ly:stencil-translate-axis
            (apply
              ly:stencil-add
              (make-grey-filled-box-stencil-list
                x-coords
                color-steps
                thick
                '()))
            ;; the actual offset is TODO, hardcoded here
            -8
            Y))
         #f)))

#(define (add-gliss m)
   (case (ly:music-property m 'name)
     ((NoteEvent)
      (set! (ly:music-property m 'articulations)
            (append
              (ly:music-property m 'articulations)
              (list (make-music 'GlissandoEvent))))
      m)
     (else #f)))

addGliss =
#(define-music-function (music)
  (ly:music?)
  (map-some-music add-gliss music))

%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXAMPLE
%%%%%%%%%%%%%%%%%%%%%%%%%

mus =
  {
    \addGliss {
      \override Glissando.stencil = #my-gliss
      b'16 b'16 b'8 b'4
      \override Staff.Beam.color = #(x11-color 'grey60)
      b'8 b'16 b'16 ~
    }
    %% n.b. If glissando-skip is #t \addGliss needs to be interrupted
    %% otherwise a programming error occurs
    \once \override NoteColumn.glissando-skip = ##t
    b'16
    \addGliss {
      b'16 b'8
    }
    %% a final target for the last glissando needs to be present, otherwise
    %% lily complains about unterminated glissando
    b'8
  }

\new Staff \mus

\new Staff {
  %% negative value reverses colors
  \override Glissando.details.color-steps = -100
  %% thicker
  \override Glissando.thickness = 2
  \mus
}

\new Staff {
  %% less steps, default (and max) is 100
  \override Glissando.details.color-steps = 5
  %% thinner
  \override Glissando.thickness = 0.2
  \mus
}

Cheers,
  Harm

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