Re: How to get bounding NoteColumns of the first of consecutive TextSpanners

[Jean Abou Samra]

Le 03/03/2021 à 13:55, Thomas Morley a écrit :
> Hi,
>
> please have a look at the following minimal, producing three staves,
> the middle one with consecutive TextSpanners:
>
> mus = { bes \startTextSpan b\stopTextSpan \startTextSpan bis\stopTextSpan }
> << { a4 a a } \mus { c' c' c' } >>
>
> Now I want to know the starting and ending NoteColumns of the _first_
> TextSpanner.
> Though, the first TextSpanner is left-bounded by NoteColumn and
> right-bounded by PaperColumn.
>
> How to get the NoteColumn at first TextSpanner's end?
>
> Below some test-code.
> Obviously I can filter PaperColumn's elements for NoteColumns, but
> PaperColumn is a Score-grob, thus I get all three.
> How to select?
> (I may not know the position of the Staff with the TextSpanners)
>
> #(define tst
>    (lambda (grob)
>      (let* ((left-bound (ly:spanner-bound grob LEFT))
>             (right-bound (ly:spanner-bound grob RIGHT))
>             (ncs-from-grob
>               (ly:grob-array->list (ly:grob-object grob 'note-columns)))
>             (right-bound-elts
>               (ly:grob-array->list
>                 (ly:grob-object right-bound 'elements)))
>             (ncs-from-right-bound
>               (filter
>                 (lambda (elt) (grob::has-interface elt 'note-column-interface))
>                 right-bound-elts))
>                 )
>      (pretty-print
>        (list
>          left-bound
>          right-bound
>          ncs-from-grob
>          (equal? left-bound (car ncs-from-grob))
>          ncs-from-right-bound
>          )))))
>
> mus = {
>    bes4-\tweak #'after-line-breaking #tst
>     \startTextSpan
>    b\stopTextSpan
>     \startTextSpan
>    bis\stopTextSpan
> }
>
> <<
>    { a4 a a }
>    \mus
>    { c' c' c' }
> Thanks,
>    Harm


Hi,

This looks tricky indeed.

Maybe an engraver operating in Voice context? Here's my attempt:

\version "2.23.1"

#(set-object-property! 'bounding-note-columns 'backend-type? pair?)

Set_bounding_note_columns_engraver =
#(lambda (context)
   (let ((spanner-starting #f)
         (spanner-ending #f)
         (note-column #f))
     (make-engraver
       (acknowledgers
         ((line-spanner-interface engraver grob source-engraver)
            (set! spanner-starting grob)
            (ly:grob-set-property! grob
                                   'bounding-note-columns
                                   ; Huh, '(#f . #f) makes a unique object?
                                    (cons #f #f)))
         ((note-column-interface engraver grob source-engraver)
            (set! note-column grob)))
       (end-acknowledgers
         ((line-spanner-interface engraver grob source-engraver)
            (set! spanner-ending grob)))
       ((stop-translation-timestep engraver)
          (if spanner-starting
              (set-car! (ly:grob-property spanner-starting 
'bounding-note-columns)
                       note-column))
          (if spanner-ending
              (set-cdr! (ly:grob-property spanner-ending 
'bounding-note-columns)
                        note-column))
          (set! spanner-starting #f)
          (set! spanner-ending #f)
          (set! note-column #f)))))


% For testing
#(use-modules (srfi srfi-26))
#(define (visualize-note-column-bounds grob)
   (let* ((cols (ly:grob-property grob 'bounding-note-columns))
          (left-col (car cols))
          (right-col (cdr cols))
          (left-note-heads (ly:grob-array->list (ly:grob-object 
left-col 'note-heads)))
          (right-stem (ly:grob-object right-col 'stem)))
     (for-each
        (cute ly:grob-set-property! <> 'color red)
        left-note-heads)
     (ly:grob-set-property! right-stem 'color blue)))

\layout {
  \context {
    \Voice
    \consists \Set_bounding_note_columns_engraver
    \override TextSpanner.after-line-breaking = 
#visualize-note-column-bounds
  }
}

mus = {
  bes4\startTextSpan
  b\stopTextSpan
   \startTextSpan
  bis\stopTextSpan\startTextSpan
  b\stopTextSpan
}

<<
  { a4 a a }
  \mus
  { c' c' c' }
>>


Like David's solution, this of course won't give you the note columns 
for each of the broken pieces. Well, I am in fact not sure that a notion 
of the bounding note columns for a broken text spanner can even be 
defined. Thoughts?

Cheers,
Jean