Re: custom VoiceFollower

[address@hidden]

On 19 juin 2012, at 14:45, address@hidden wrote:

> Hey all,
> 
> Does anyone have any idea why the custom-rolled VoiceFollower isn't printing 
> in the example below?  I'm positive the grob is being created and that it is 
> linking successive notes (check out the print to the command line to see the 
> info).
> 
> Cheers,
> MS
> 
> \version "2.14.2"
> 
> #(define (define-grob-property symbol type? description)
>  (if (not (equal? (object-property symbol 'backend-doc) #f))
>      (ly:error (_ "symbol ~S redefined") symbol))
> 
>  (set-object-property! symbol 'backend-type? type?)
>  (set-object-property! symbol 'backend-doc description)
>  symbol)
> 
> #(define-grob-property 'link-me boolean? "Link two grobs.")
> 
> changeEngraver =
>    #(let ((note-head-list '()))
>       (list
>         (cons 'acknowledgers
>               (list
>                 (cons 'note-head-interface
>                       (lambda (engraver grob source-engraver)
>                         (if (ly:grob-property grob 'link-me #f)
>                           (set! note-head-list (cons grob 
> note-head-list)))))))
>         (cons 'process-acknowledged
>               (lambda (trans)
>                 (if (= 2 (length note-head-list))
>                   (let ((grob (ly:engraver-make-grob trans
>                                                      'VoiceFollower
>                                                      (cadr note-head-list))))
>                     (ly:spanner-set-bound! grob LEFT (car note-head-list))
>                     (ly:spanner-set-bound! grob RIGHT (cadr note-head-list))
>                     (set! note-head-list '())))))))
> 
> \layout { \context { \Score \consists \changeEngraver } }
> 
> \new Staff \relative c' {
>  \override NoteHead #'link-me = ##t
>  \override Score.VoiceFollower #'stencil =
> #(lambda (grob)
>  (format #t "INFO ~a ~a\n"
>    (ly:grob-property grob 'left-bound-info)
>    (ly:grob-property grob 'right-bound-info))
>  (ly:line-spanner::print grob))
>  a1 b \break c d \break e f \break g a
> }

Own question answered, got left and right bounds backwards.

Cheers,
MS