Re: Glissando stems

[Thomas Morley]

Am Mo., 8. Aug. 2022 um 16:35 Uhr schrieb Mark Knoop <mark@opus11.net>:
>
> Following on from this old thread...
>
> https://lists.gnu.org/archive/html/lilypond-user/2019-10/msg00405.html
>
> ... I'm using Harm's fantastic code to align/attach Stems to a Glissando line.
>
> However, I've come across a problem with the code which in relation to 
> MultiMeasureRests. Namely, writing a MMR which will appear on the same system 
> as the Glissando (or some other situations) results in an error:
>
> ERROR: In procedure ly:item-get-column: Wrong type argument in position 1 
> (expecting Item): #<Grob Spanner >
>
> Attached is Harm's original code with a few lines added to the example (at 
> line 595) which demonstrate the problem.
>
> Many thanks,
>
> Mark
>
>
> --
> Mark Knoop

Hi Mark,

`ly:item-get-column' used in bultin `grob::when' sometimes causes the
problem, if blindly thrown at all system's elts, as I do in said
coding.
It's fixable by prefiltering for NoteColumns, i.e. line 102ff should read:

                 ;; Filter for every inner (skipped) NoteColumn
                 (inner-ncs
                   (filter
                     (lambda (elt)
                       (let (;; Going for `ly:grob-relative-coordinate´ disturbs
                             ;; vertical spacing, thus we sort/filter using
                             ;; `grob::when´
                             (elt-when (grob::when elt)))
                         (and
                           (ly:grob-property elt 'glissando-skip #f)
                           (ly:moment<? left-bound-when elt-when)
                           (not (moment<=? right-bound-when elt-when)))))
                     (filter
                       (lambda (elt)
                         (grob::has-interface elt 'note-column-interface))
                         (ly:grob-array->list sys-elts-array))))

That said, meanwhile I don't like the whole approach anymore...
The need to recreate things LilyPond already has done is an alarm
sign. Maybe there are other still uncovered bugs.
Alas, I don't have a working alternative :(

HTH a bit,
  Harm