Re: cross-staff, broken Glissando

[Thomas Morley]

Am So., 7. Nov. 2021 um 14:00 Uhr schrieb Jean Abou Samra <jean@abou-samra.fr>:

> >>> That said,...
> >>> If I always compensate the right ending-point with (pseudo-code)
> >>> (ly:grob-relative-coordinate <Glissando-grob> <System-grob> Y)
> >>> Then the crosses are at those positions Mike's patch promises.
> >> Really System? Isn't this going to create a
> >> cyclic dependency between the stencil and
> >> vertical alignment for non-cross-staff glissandi
> >> via VerticalAxisGroup skylines? Off the top I would
> >> think it should be a matter of correcting
> >> reference points (see above).
> > I compile with recent master, so your added warnings for  cyclic
> > dependencies may pop up.
> > They don't.
>
>
> Ah, because vertical alignment works via
> ly:grob-translate-axis! and doesn't mark the
> dependencies. Sigh.
>
> Look at:
>
> <<
>    \new Staff {
>      c'1
>    }
>    \new Staff {
>      \override Glissando.stencil =
>        #(lambda (grob)
>           (ly:message "~s"
>                       (ly:grob-relative-coordinate
>                         grob
>                         (ly:grob-system grob)
>                         Y))
>           (ly:line-spanner::print grob))
>      c'1\glissando c''1
>    }
>  >>
>
> It prints "0.0". So there's no cyclic dependency
> warned about, but it's not doing what you intend.
> How could it? The glissando is part of the vertical
> skylines of the VerticalAxisGroup. These are the
> basis for vertical alignment. So you need the glissando's
> stencil before you can take the Y coordinate of the
> glissando relative to the system. Unless you have
> a cross-staff glissando, because these aren't part
> of the skylines -- but even then there is usually no
> reason to take the root system and not just a refpoint
> computed generically for both non-cross-staff
> and cross-staff grobs.

For non-cross-staff Glissando it returns always zero, yes, for
cross-staff a certain value is found:

<<
   \new Staff = "top" {
     c'1
   }
   \new Staff {
     \override Glissando.stencil =
       #(lambda (grob)
          (ly:message "~s"
                      (ly:grob-relative-coordinate
                        grob
                        (ly:grob-system grob)
                        Y))
          (ly:line-spanner::print grob))
     c'1\glissando \change Staff = "top" c''1
   }
 >>

-> -12.779

I tend to think: nice, let us always add this value, in any case it
only matters for cross-staff at all.

Why not?


Cheers,
  Harm