Re: tweaking beam length

[Thomas Morley]

2013/5/16 luis jure <address@hidden>:
>
> dear list,
>
> the output of the following code is shown in the first attached image:
>
> \version "2.17.17"
>
> \score {
>     \new Voice \with {
>       \remove "Forbid_line_break_engraver"
>       \override Beam.breakable = ##t
>     }
>
>       \relative c'' {
>         \repeat unfold 5 { c2. \repeat unfold 2 { c8[ c16] } c8 c2. } }
>   \layout { }
> }
>
>
> i find the beams after the break (m. 6) too long, but i don't know how to
> modify them. i'd like to get something like in the second image. is there
> a property that i could somehow adjust? i tried a couple of searches in
> the manual but i couldn't find anything appropriate.
>
> best,
>
>
> lj

Hi Luis,

I suppose noone thought about this case before.
At least, every version since 2.12.3 (the oldest on my computer) shows
two beams of equal length at line-begin.
Worth a bug-report, I think.

Meanwhile you may want to use the function below.
Comments in code, if something isn't clear, shout.

\version "2.16.0"

shortenBrokenBeams =
#(define-music-function (parser location amount)(number-list?)
"
 Shorten broken Beams after line-break.

 We get the 'beam-segments, rebuilding it modified.
 The 'beam-segments-property is an alist of type:
    '(((vertical-count . 0) (horizontal 3.865018 . 5.93))
      ((vertical-count . 1) (horizontal 3.865018 . 5.93)))

    `vertical-count' is the beam-count.
    `horizontal' is the X-extent relative to 'System's 'line-width.

 Applying it only if the left-bound of the 'Beam is 'NonMusicalPaperColumn,
 i.e after a line-break.
 Affecting a broken Beam at line-end is possible, too, but not yet coded.
"
#{
  %% Add \once ?
  \override Score.Beam #'beam-segments =
    #(lambda (grob)
       (let* ((beam-segments (ly:beam::calc-beam-segments grob))
              (grob-name
                 (lambda (x) (assq-ref (ly:grob-property x 'meta) 'name)))
              ;; TODO: better coding, use set-car! or ...
              (rebuild-beam-segments-proc
                 (lambda (vertical-count horizontal shorten)
                         (cons
                           (cons 'vertical-count vertical-count)
                           (list
                             (cons 'horizontal
                               (cons (- (car horizontal) shorten)
                                     (cdr horizontal))))))))

       (if (eq? (grob-name (ly:spanner-bound grob LEFT)) 'NonMusicalPaperColumn)
           (begin
              (let* ((horizontals
                        (map
                          (lambda (x) (assoc-get 'horizontal x))
                          beam-segments))
                     (vertical-counts
                        (map
                          (lambda (x) (assoc-get 'vertical-count x))
                          beam-segments))
                     (new-beam-segments
                          (map
                            rebuild-beam-segments-proc
                            vertical-counts horizontals amount)))

       ;;;; If you want to compare the default and the changed
       ;;;; settings, uncomment the following lines.
              ;; (let ((new-horizontals
              ;;           (map
              ;;             (lambda (x) (assoc-get 'horizontal x))
              ;;             new-beam-segments)))
              ;;      (display "\n\thorizontals \t")(write horizontals)
              ;;      (display "\n\tnew-horizontals ")(write new-horizontals))

              new-beam-segments))
           beam-segments)))
#})

\score {
    \new Voice \with {
      \remove "Forbid_line_break_engraver"
      \override Beam #'breakable = ##t
    }
        \relative c'' {
         \shortenBrokenBeams #'(-1.5 -3.6)
          \repeat unfold 5 { c2. \repeat unfold 2 { c8[ c16] } c8 c2. } }
        \layout { }
}


HTH,
  Harm

affect-broken-beams-length.png
Description: PNG image