Re: Terminology of baseMoment, beats, groups

[Urs Liska]

Am 11.11.2017 um 11:42 schrieb David Kastrup:
> Urs Liska <address@hidden> writes:
>
> > So, now the first question ...
> >
> > The terminology of baseMoment, beats and groups is inconsistent
> > between the NR
> > (http://lilypond.org/doc/v2.19/Documentation/notation/beams#setting-automatic-beam-behavior)
> > and the code. The question is, what are the components of the
> > following:
> >
> >    \set baseMoment = #(ly:make-moment 1/8)
> >    \set beatStructure = 3,3,2
> >
> >  From the text in the NR this would be three beats, divided in three or
> > two base moments each.
> > However, the C++ code (and the code comments) refer(s) to that as
> > three groups with three beats each.
> Can you please come up with actual quotes/evidence for those statements?
> Neither of those make much sense, so I'd guess you'd been
> over-paraphrasing either.  Or alternatively, there are grave errors in
> the respective description which warrant fixing rather than unifying
> first.

a) from the NR section linked
"beatStructure is a scheme list that defines the length of each beat in 
the measure in units of baseMoment. "

I read this as: In the given example beatStructure is a list that 
defines the measure to consist of three beats. Beat one and two have the 
length of three baseMoments of 1/8, beat three is two baseMoments of 1/8 
long.

Actually this is consistent with how I would describe that measure in 
prose: we have an 8/8 measure with three beats, with lengths 3, 3, and 2 
quavers.


b) from beaming-pattern.cc

1) line 206ff., comment to find_location()
/*
   Get the group start position, the next group starting position, and the
   next beat starting position, given start_moment, base_moment,
   grouping, and factor
*/

2) line 265, comment right after find_location has been called:
// Mark the importance of stems that start at a beat or a beat group.

From the actual behaviour of the code (and other comments throughout 
the code) it is clear that "beat" refers to a baseMoment unit and 
"group" refers to the entity the NR calls "beat".
The context property "beatStructure" obviously corresponds to the C++ 
variable "grouping".