Re: Automatically identify beats

[Thomas Morley]

Am So., 7. Okt. 2018 um 15:59 Uhr schrieb Aaron Hill <address@hidden>:
>
> On 2018-10-07 4:29 am, Thomas Morley wrote:

> > Below my own attempt using an engraver (to have access to the
> > 'timeSignatureFraction, a context-property, and to Stem/NoteHead-grobs
> > in one go).
> > [ . . . ]
>
> That is definitely something I will have to review in detail, as I have
> not yet worked with engravers and contexts obviously still have a lot to
> learn.
>
>
> -- Aaron Hill

There are not many ways to access grobs and contexts at the same time.
I think, engravers are the most general.
We have some examples of scheme-engravers in the regression-tests.
(And in the archives of the mailing-list ofcourse.)
A good starting point is ‘scheme-engraver.ly’ from:
http://lilypond.org/doc/v2.19/input/regression/collated-files.html
It demonstrates all possible "entry-points".

http://lilypond.org/doc/v2.19/Documentation/contributor-big-page#engraver-tutorial
gives some documentation. It's for C++, but things are not very
different for scheme.

If you have too much time, you may have a look at ‘scheme-engraver.ly’ from
http://lilypond.org/doc/v2.13/input/regression/collated-files.html
The newer file uses the great 'make-engraver'-macro (by David Kastrup).
Otoh, this macro hides an engraver _is_ a list (which is obvious, if
you look in the older file).
I had found it useful to observe the list-syntax for a long time, even
after the make-engraver-macro was out.
Helped me learning.

Cheers,
  Harm