Re: TimeSignature with note in denominator

[David Kastrup]

Aaron Hill <lilypond@hillvisions.com> writes:

> On 2021-11-13 6:14 am, Kieren MacMillan wrote:
>>> Functions can accept ly:music? and you can drill down to determine if
>>> it contains TimeSignatureMusic and modify its properties.  The only
>>> issue is that currently \time (and TimeSignatureMusic) require the
>>> denominator to be a number.  You can convert 2/4. to its logical
>>> equivalent of 6/8 but key information is lost.  \note-denom cannot
>>> magically recover the original intention to be able to render the
>>> signature as the user wanted.
>> If 2/4. is the value entered, do we have access to the num (2) after
>> the conversion to 6/8 has happened? If so, I could “reverse engineer”
>> the 2/4. from (num . denom) = (6 . 8).
>
> Only if the music function that accepts the input is able to store
> that information somewhere that can be referenced at the time the
> TimeSignature grob gets *stencilized*.  (Is that a word?)

Time_signature_performer does not have access to a grob.

> I took a quick look at the source, so let me try to summarize the flow
> of information as I see it:
>
> 1. User provides a \time command as input.
>    There are two arguments for this command, beat-structure and
>    fraction.  beat-structure is optional, defaulting to a null list,
>    but otherwise it expects a number-list.  fraction is, well, a
>    fraction (index-pair) that must be specified.  The \time command
>    then constructs TimeSignatureMusic with the specified numerator,
>    denominator, and beat-structure as music properties.
>
> 2. make-time-signature-set is the callback for TimeSignatureMusic.
>    This callback processes the information from TimeSignatureMusic and
>    sets various timing-related context properties.  Additionally, a
>    time-signature-event is broadcast, although nothing currently
>    listens for this event.

Huh?

$ git grep listen_time_signature
lily/time-signature-engraver.cc:  void listen_time_signature (Stream_event *);
lily/time-signature-engraver.cc:Time_signature_engraver::listen_time_signature 
(Stream_event *ev)
lily/time-signature-performer.cc:  void listen_time_signature (Stream_event *);
lily/time-signature-performer.cc:Time_signature_performer::listen_time_signature
 (Stream_event *ev)

-- 
David Kastrup