Re: Align above "current" staff

[Urs Liska]

Hi David,

Am 07.07.2018 um 16:15 schrieb David Kastrup:

Urs Liska <address@hidden> writes:

Hi all,

I want a music function to produce an ossia staff. The NR states that
in order to place that above alignAboveContext should be used:

\new Staff = "main" \relative {
  c''4 b d c
  <<
    { c4 b d c }

    \new Staff \with {
      \remove "Time_signature_engraver"
      alignAboveContext = #"main"
      \magnifyStaff #2/3
      firstClef = ##f
    }
    { e4 d f e }
  >>
  c4 b c2
}

But is that also possible when I  (or my music-function) doesn't know
the staff's name

You can use \applyContext for getting it before you initiate your own
(hopefully uniquely named) Staff.

Thank you for the suggestion, which looks like it's what I need. However, unfortunately I didn't get anywhere looking at the various examples in the docs. It's still a mystery to me what does what and evaluates to what and when that happens or not ...

OK, \applyContext passes the current context as the single argument to a function. Within that function one can access (retrieve and set) the properties of that context. I can sort of understand what that does in the example with "desaturating" colors.

But that function call always returns a (make-music 'ApplyContext ...) music _expression_, which is nothing I can use for my purposes, it seems everything is about the side-effects.

So I thought I'd define a variable and have the \applyContext function populate that variable with the context name, so I could use that later. But that doesn't work either, it looks like the \applyContext is only executed *after* I would need to use the variable:

\version "2.19.80"

ossia =
#(define-music-function
  (music ossia-music) (ly:music? ly:music?)
  (let ((name "initialized"))
    #{
      \applyContext
      #(lambda (context)
         (set! name (ly:context-id (ly:context-parent context))) ; I know this has to be more robust ...
         (ly:message "1. context name inside \\applyContext: ~a" name)
         ; the following \new Staff has no effect
         #{ \new Staff { c' } #})
      #(ly:message "2. context name after \\applyContext was called: ~a" name)
      #music
      % Create \new Staff with ossia-music
    #}))

\new Staff = "My Staff"
\relative {
  g'8 a b c
  \ossia { d c b a } { c b a g }
  g b d b g2
}

=>
Parsing...
2. context name after \applyContext was called: initialized
Interpreting music...
1. context name inside \applyContext: My Staff

I'm sorry, but I need more concrete pointers or even an example.

Thanks
Urs