Hi all,
Follow up question: is there a way to know the "parent" of the voices as they
are defined in the code?
In the following example, I would like to determine that voice "two" splits off
from voice "one" without relying on the context-id.
(ly:context-parent ctx) gives me the staff, not the "parent voice"...
\score {
\new Staff {
\time 2/2
<<
\new Voice = "one" {
\relative c'' {
\voiceOne
g8 e
}
<<
\new Voice = "two" {
\voiceOne
\relative c'' { a8. g16 f8 e16 f g f e d }
}
\new Voice = "three" {
\voiceTwo
\relative c' { c8 a d8. c16 b8 a16 b }
}
>>
}
\new Voice = bottom {
\voiceTwo
\relative c' { g1 }
}
>>
}
}
Thanks in advance!
cheers
Maurits
> Van: Aaron Hill <lilyp...@hillvisions.com>
> Onderwerp: Antw.: detecting the start and end of a polyphonic passage from
> scheme
> Datum: 25 juni 2020 17:12:13 CEST
> Aan: lilypond-user@gnu.org
>
>
> On 2020-06-25 7:01 am, Maurits Lamers wrote:
>> Hi all,
>> I am trying to build a system based on the listener system which can
>> identify voices in a piece of music.
>> I use a listener to the Voice context to give me the note events.
>> In the following passage I can use (ly:context-id
>> (ly:translator-context engraver) to get the id, which is empty for c4,
>> "1" for the first voice, "2" for the second voice, and empty again for
>> d4 at the end.
>> time 4/4 \relative c' { c4 << { c8 d e4 } \\ { c8 b c4 } >> d4 | }
>> However in the following passage the context-id cannot be used because
>> it is not set.
>> \relative c' {
>> \new Voice {
>> c4
>> <<
>> \new Voice {
>> c8 d e4
>> }
>> \new Voice {
>> c8 b c4
>> }
>> >>
>> d4
>> }
>> }
>> I am currently using object properties to follow these voices by
>> setting a unique value for that voice context object, but that doesn't
>> help me
>> to detect properly the start and end of the polyphonic passage. The
>> main voice gets 1, the first nested voice will be 2, the second nested
>> voice will be 3.
>> For transcription purposes it would be very helpful to detect the
>> start and end of the polyphonic passage. Is this possible?
>
> The initialize and finalize procedures of an engraver will run when the
> context in which it is \consisted begins and ends. Consider:
>
> %%%%
> \version "2.20.0"
>
> #(define custom-uid
> (let ((custom-uid-prop (make-object-property))
> (last-uid 0))
> (lambda (obj)
> (or (custom-uid-prop obj)
> (begin
> (set! last-uid (1+ last-uid))
> (set! (custom-uid-prop obj) last-uid)
> last-uid)))))
>
> handle-init-and-final =
> #(lambda (context)
> (make-engraver
> ((initialize engraver)
> (let* ((ctxt (ly:translator-context engraver))
> (id (ly:context-id ctxt))
> (uid (custom-uid ctxt))
> (now (ly:context-now ctxt)))
> (format #t "\ninitialize: ~s, id=~s, uid=~s, now=~s"
> ctxt id uid now)))
> ((finalize engraver)
> (let* ((ctxt (ly:translator-context engraver))
> (id (ly:context-id ctxt))
> (uid (custom-uid ctxt))
> (now (ly:context-now ctxt)))
> (format #t "\nfinalize: ~s, id=~s, uid=~s, now=~s"
> ctxt id uid now)))))
>
> \layout { \context { \Voice \consists \handle-init-and-final } }
>
> { \relative c' { \new Voice { c4
> << \new Voice = foo { \voiceOne c8 d e4 }
> \new Voice { \voiceTwo c8 b c4 } >> d4 } } }
> %%%%
>
> ====
> . . .
> Parsing...
> Interpreting music...
> initialize: #<Context Voice () >, id="", uid=1, now=#<Mom -infinity>
> initialize: #<Context Voice=foo () >, id="foo", uid=2, now=#<Mom 1/4>
> initialize: #<Context Voice () >, id="", uid=3, now=#<Mom 1/4>
> finalize: #<Context Voice=foo () >, id="foo", uid=2, now=#<Mom 3/4>
> finalize: #<Context Voice () >, id="", uid=3, now=#<Mom 3/4>
> finalize: #<Context Voice () >, id="", uid=1, now=#<Mom 1>
> Preprocessing graphical objects...
> . . .
> ====
>
> NOTE: I am using Scheme object properties to attach a custom unique
> identifier to the contexts as they are seen, so it is possible to discern
> which context is which even when they are not named.
>
>
> -- Aaron Hill
>
>
>
>
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