Re: "Pausing" Voice

[David Kastrup]

Thomas Morley <thomasmorley65@gmail.com> writes:

> Am Do., 9. Juli 2020 um 12:30 Uhr schrieb David Kastrup <dak@gnu.org>:
>>
>> Thomas Morley <thomasmorley65@gmail.com> writes:
>>
>> > Hi all,
>> >
>> > if temporary Voices occur, then the main Voice may not contain
>> > rhythmic-events for the duration of those temporary Voices.
>> > I'd like to identify where the main Voice "pauses", like in this test-code:
>>
>> Just a vague idea: does the busyGrobs context property maintained by the
>> Grob_pq_engraver help in any manner?
>
> Hi David,
>
> I tried:
>
> \version "2.20.0"
>
> #(define (print-busy-grob-info context)
>   (let ((busy-grobs (ly:context-property context 'busyGrobs)))
>     (if (pair? busy-grobs)
>         (for-each
>           (lambda (bg)
>             (format #t "\nAt ~a we see ~a ending at ~a, pitch is ~a"
>               (ly:context-current-moment context)
>               (cdr bg)
>               (car bg)
>               (ly:prob-property (ly:grob-property (cdr bg) 'cause) 'pitch)))
>           busy-grobs)
>         (format #t "\nAt ~a no busy grobs "
>           (ly:context-current-moment context)))))
>
> Test_busy-grob_engraver =
> #(lambda (context)
>   (make-engraver
>     ((process-music this-engraver)
>       (print-busy-grob-info context))))
>
> \new Voice
>   \with {
>     \consists \Test_busy-grob_engraver
>   }
>   {
>     %% mom 0
>     b1\startTextSpan\((
>     %% mom 1
>     \new Voice c'
>     %% mom 2
>     d'\stopTextSpan)\)
>     %% mom 3
>   }
>
> ==>
> At #<Mom 0> no busy grobs
> At #<Mom 1> we see #<Grob NoteHead > ending at #<Mom 1>, pitch is #<Pitch b >
> At #<Mom 2> no busy grobs
> At #<Mom 3> we see #<Grob NoteHead > ending at #<Mom 3>, pitch is #<Pitch d' >
>
> Which is very nice at first sight.
>
> Alas, in IR busyGrobs is described as:
> "
> busyGrobs (list)
>
> A queue of (end-moment . grob) cons cells. This is for internal (C++)
> use only. This property contains the grobs which are still busy (e.g.
> note heads, spanners, etc.)."
>
> In the above posted output I miss the spanners, though. To be clear,
> in my use-case I'll _wish_ to disregard spanners. I'm only interested
> in rhythmic-events, including skip-events.
> Can I rely on the busyGrobs-description being wrong?

I checked.  Grob_pq_engraver listens to everything with grob-interface.
The internals guide rather looks like this would also concern spanners.

However, the only grobs that are being entered are ones having a
non-zero duration (most spanners don't but rather have start/end events)
and that don't have the multi-measure-interface (multi-measure rests are
one example of spanners with a duration).  I am not sure just what this
may then leave in terms of spanners.  I cannot really think of one off
the bat, but there is nothing explicitly prohibiting it.

> Furthermore, I think I need to do some settings in
> stop-translation-timestep. There the output would be different,
> 'busyGrobs is never '(), according to my tests.
> So I would need to read 'busyGrobs in process-music and carry over the
> results to stop-translation-timestep to rely on it.
> If busyGrobs may contain spanners or other not-rhythmic-events I'd
> need to do some selections.
>
> Thus the question is, whats cheaper:
> (1) calculating, based on current-moment and 'length of the
> rhythmic-event (as in my initial post)?
> (2) reading busyGrobs, move the result, probably select for rhythmic
> grobs? Would this work for skips as well?

Skips aren't grobs, are they?

> Any advice?

Not really.  That was just something I remembered that seemed related to
the task you are trying to do.  The only engravers that look at
busyGrobs seem to be Lyric_engraver , Rest_collision_engraver , and
Forbid_line_break_engraver .

It's pretty obscure.

-- 
David Kastrup