thank you for the explanations and the example.
On first sight it looks like I'll be able to get where I want
with that. Although of course it'll be pretty complex (maybe
"messy" would be more honest) once I try to transplant it from the
MWE to the actual case ;-)
But I'll have to do that later ...
Urs Liska <address@hidden> writes:
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.
Ok, that was probably less than helpful.
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.
Sure. And the side-effect you want is setting the alignAboveContext
context property. Which is not trivial if the context does not even
exist yet. Cough cough. It would be possible to \once\set
alignAboveContext in the mother context and let it be inherited but if
the mother context does not yet have a vertical axis group of its own,
this is going to end up one ugly mess.
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)
This is being called during iteration. It is only during
iteration that contexts actually exist.
; the following \new Staff has no effect
#{ \new Staff { c' } #})
The return value of applyContext, in this case a music
_expression_, is not being used.
#(ly:message "2. context name after \\applyContext was called: ~a" name)
This is being called during input, even before LilyPond's parser
reads the following line (whatever may be in it and which ever
music _expression_ or score it may end up being used or even not
used).
#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.
I'll do an example in the spirit of my hand-waving original proposal but
it's, well, not pretty.