Re: Beam subdivision

[Thomas Morley]

2015-03-10 22:29 GMT+01:00 Trevor Daniels <address@hidden>:
> tisimst wrote Tuesday, March 10, 2015 4:52 PM
>
>> The other question the OP was asking is can
>> the group default to have TWO full beams
>> across the group, ...
>> I had a look through the IR and couldn't find
>> anything that says it will only use a SINGLE
>> beam across the whole group.
>
> The snippet in NR 1.2.4 Beams which shows how to subdivide beams says:
>
> "When set, multiple beams will be subdivided at intervals defined by the 
> current value of baseMoment by reducing the multiple beams to just one beam 
> between the sub-groups."
>
> But you're right in the sense that there is no accessible property that 
> controls the number of inter-group beams, and there should be, or even 
> better, LilyPond should just do the correct subdivision if subdivideBeams is 
> set.  In "Behind Bars", on pages 156-157, Elaine Gould makes it quite 
> explicit that using a single beam to separate groups of four 64th notes is 
> wrong.  She says, "the number of beams separating the groups [should be] 
> equal to the duration of the groups they separate".  A group of four 64th 
> notes equals a 16th, so two such groups should be separated by a 16th beam, 
> i.e. two beams.  Four such groups should have two beams between first and 
> second and between third and fourth groups, and a single beam between second 
> and third.  She gives an example showing exactly this.
>
> There is an enhancement request for this: see
> https://code.google.com/p/lilypond/issues/detail?id=2361
>
> Trevor


I'm with Trevor, LilyPond's default should do it correctly, if
subdivideBeams = ##t

Nevertheless, maybe the following is of some help for the current request.
Although trying to typeset the example David Bobroff gave in said
issue is not really convincing.



\version "2.19.16"

set-connected-beam-counts =
#(define-music-function (parser location val music)(integer? ly:music?)
#{
  \temporary
    \override Stem.after-line-breaking =
      #(lambda (grob)
        (let*((beaming (ly:grob-property grob 'beaming)))
         (if (>= val 0)
             (begin
               (if (and (list? (car beaming))
                        (= (caar beaming) 0))
                   (ly:grob-set-property! grob 'beaming
                     (cons (iota val) (cdr beaming))))

               (if (and (list? (cdr beaming))
                        (= (cadr beaming) 0))
                   (ly:grob-set-property! grob 'beaming
                     (cons (car beaming) (iota val)))))
              (ly:message "negative beam-count detected, ignoring"))))
  $music
  \revert Stem.after-line-breaking
#})


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

\paper { line-width = 80 indent = 0 }

mI = \tuplet 5/4 { e,32[ c' bes e d bes' g d' d, aes'] \bar "" \break }

mII = \tuplet 5/4 { e,128[ c' bes e d bes' g d' d, aes'] \bar "" \break }
mIII = { c64[ d e f g f e d c d e f] \bar "" \break }

\version "2.18.2"

\relative c'' {
  \cadenzaOn

  \set subdivideBeams = ##t

  \set beatStructure = #'(5)
  \set baseMoment = #(ly:make-moment 1/20)

  \set-connected-beam-counts 2
  \mI

  \set baseMoment = #(ly:make-moment 1/80)

  \set-connected-beam-counts 0
  \mII

  \set-connected-beam-counts 1
  \mII

  \set-connected-beam-counts 2
  \mII

  \set-connected-beam-counts 3
  \mII

  \set-connected-beam-counts 4
  \mII

  \set-connected-beam-counts 5
  \mII

  \set-connected-beam-counts 6
  \mII

  \set-connected-beam-counts 7
  \mII

  \set baseMoment = #(ly:make-moment 2/64)
  \set-connected-beam-counts 1
  \mIII

  \set baseMoment = #(ly:make-moment 3/64)
  \set-connected-beam-counts 2
  \mIII

  \set baseMoment = #(ly:make-moment 4/64)
  \set-connected-beam-counts 3
  \mIII
}

%% https://code.google.com/p/lilypond/issues/detail?id=2361
%% typesetting the example by David Bobroff

\relative c {
  \clef bass
  \key e \major
  \omit Staff.TimeSignature
  \time 3/8

  \set subdivideBeams = ##t
  \set baseMoment = #(ly:make-moment 1/16)

  fis8~

  fis32.
  \set-connected-beam-counts 2
  { gis64 fis32.} gis64
  fis32.
  \set-connected-beam-counts 2
  { gis64 fis32. }
  gis64
}



Cheers,
  Harm