Re: How to change the stem-length?

[Thomas Morley]

Hi Mike,

2011/11/7 address@hidden <address@hidden>

(...)

The function will be consistent if you hijack a different property.  To wit, quantized-positions.  By the time you call ly:beam::print, the stencil values for the stem may have already been cached, in which case they will not be recalculated for length.

Cheers,
MS

\version "2.15.16"

#(set-global-staff-size 20)

#(define ((stem-change y) grob)

 (let ((pos (ly:beam::set-stem-lengths grob)))
    (begin

      (ly:grob-set-property! grob 'color red)
      (map
        (lambda (n)
          (ly:grob-set-property! n 'length y))
            (ly:grob-array->list (ly:grob-object grob 'stems))))

 pos))

%---- Test

top = \change Staff = "1"
bottom = \change Staff = "2"

music = \relative c {

      \override Beam #'auto-knee-gap = #0

      \override Beam #'quantized-positions = #(stem-change 20)

       \bottom c32[ g' \top eis'']
       c[ b \bottom  g,]
       \top e''[ \bottom c,, \top  g'']
       \bottom c,,64[ \top g'' e' \bottom c,, \top  c'']
       f,,32 [f''' f,,, f''']
}

\score {
 \new PianoStaff <<
  \new Staff = "1" {
    s4 s8 s16
  }
  \new Staff = "2" {
    \clef bass
    \music
  }
 >>
}

many thanks. Now it works fine. 
But using the 'quantized-positions-property, I've no success with integrating a new stencil. Trying the following, I retrieve always the new stem-length, though, the "dummy-stencil" isn't printed every time.

How to do?

\version "2.15.13"

#(define (dummy-stencil grob)
   (grob-interpret-markup grob (markup #:with-color red #:rotate 10 "test-dummy")))

#(define ((stem-change y) grob)
 (let ((pos (ly:beam::set-stem-lengths grob)))
    (begin
      (map
        (lambda (n)
          (ly:grob-set-property! n 'length y))
            (ly:grob-array->list (ly:grob-object grob 'stems)))
      (ly:grob-set-property! grob 'stencil dummy-stencil)
    )
 pos))

%---- Test

\relative c' {
        \override Beam #'quantized-positions = #(stem-change 20)
      c32[ d e f g a b c] s128
      c,32[ d e f g a b c] s128
}

top = \change Staff = "1"
bottom = \change Staff = "2"

music = \relative c {
       
        \override Beam #'auto-knee-gap = #0

        \override Beam #'quantized-positions = #(stem-change 20)

        \bottom c32[ g' \top eis'']
        c[ b \bottom  g,]
        \top e''[ \bottom c,, \top  g'']
        \bottom c,,64[ \top g'' e' \bottom c,, \top  c'']
        f,,32 [f''' f,,, f'''] c,,32[ d e f g a b c]
}

\score {
  \new PianoStaff <<
    \new Staff = "1" {
      s4 s8 s16 s4
    }
    \new Staff = "2" {
      \clef bass
      \music
    }
  >>
} 

Best,
  Harm