Re: Different default arpeggio positions

[Thomas Morley]

Hi Jean,

Am Do., 1. Dez. 2022 um 09:48 Uhr schrieb Jean Abou Samra <jean@abou-samra.fr>:

> This is a widespread but bad coding pattern that I regularly advise
> against on this list :-)

you'll find a plethora of snippets in the archives using
after-line-breaking authored by me.
Likely starting in 2.12.3.

> It seems that when people notice they can set grob properties
> in after-line-breaking, they start using after-line-breaking
> for anything and everything, while that is not its purpose.

Well, the purpose of after-line-breaking was not well documented back
those days.
And in 2.23. IR still reads:
"Dummy property, used to trigger callback for after-line-breaking."
This is a collection of words making little sense, at least without
further explanations.

> The problem here is that after-line-breaking is run *just* after
> line breaking. It happens before LilyPond has done page spacing,
> i.e., layout out systems and staves vertically.

This is not documented afaik.

> For a cross-staff
> arpeggio, the positions depend on the distance between the
> two staves, so you are requesting 'positions earlier than LilyPond
> can provide it to you.
>
> In general, cross-staff objects are treated specially. For
> a normal arpeggio, LilyPond will request the arpeggio's
> stencil, to build the staff's skylines, and stencil will
> read positions. For a cross-staff arpeggio, which LilyPond
> recognizes by its cross-staff property set to #t, LilyPond
> refrains from reading the stencil before page layout is done,
> knowing that it needs to depend on page layout.
>
> The proper solution is to stop assuming that positions is
> available at a specific point, and instead write a callback
> that computes it as soon as it is asked for:
>
> \version "2.23.82"
>
> \score {
>    <<
>      \new PianoStaff <<
>        \new Staff = "pianoRH" \pianoRH
>        \new Staff = "pianoLH" \pianoLH
>      >>
>    >>
>    \layout {
>      #(use-modules (ice-9 match))
>      \context {
>        \Score
>        \override Arpeggio.positions =

Furthermore, grob-transformer is not very old....
In older versions one had to code far more complex
or
use after-line-breaking - with its limitations.

>          #(grob-transformer
>            'positions
>            (lambda (grob original)
>              (match original
>                ((a . b) (cons (- a 0.5) (+ b 1.0)))
>                (x x))))
>      }
>    }
> }
>
>
>
> Best,
> Jean
>
>

Ofcourse you're right advertising  not to use after-line-breaking for
all and everything.
Though, I do understand why it's still in use.

Just my 2 cents,
  Harm