Re: Ambitus

[Neil Puttock]

On 27 February 2010 15:03, David Kastrup <address@hidden> wrote:

> But wouldn't scores in a book use separate engraver instantiations and
> have separate ambitus for that reason?

Not until Nicolas's commit today.

In any case, it doesn't seem appropriate to use a scheme engraver
here, since there are no grobs created or context properties set.

> Uh, what's with the $defaultheader here?

Oops, I missed a rather important line when pasting, which should make it clear:

\header { subtitle = \markup \fromproperty #'header:ambitus }

>>    (ly:parser-define! parser 'pitches '())
>>    (ly:parser-define! parser 'key-list '())
>
> What does that do?  Why per-parser?

It's equivalent to doing

pitches = #'()
"key-list" = #'()

or

#(define pitches '())
#(define key-list '())

They're just global variables used to store information from the music
so it can be passed to the ambitus markup.

>
>>    (let* ((global (ly:make-global-context $defaultlayout))
>>           (listener (ly:make-listener process-event))
>>           (global-disp (ly:context-events-below global)))
>>
>>      (ly:connect-dispatchers (ly:make-dispatcher) global-disp)
>>      (add-stream-listener global listener 'note-event 'key-change-event 
>> 'Finish)
>>      (ly:interpret-music-expression music global)
>>      music))
>
> What does this do?  Route the music expression through a parser with a
> simple listener, then regurgitate it for the outer context?

It just interprets the parsed music expression and listens for some
interesting events (it's a lazy way of getting information out of the
music).

> It would seem that this approach would not work when you want, say, an
> ambitus per Voice, and the input is not continuous, but repeatedly
> switches between contexts.
>
> Then you don't have the whole music available as one music expression.

True, though it's only designed to work with songs having a single vocal line.

Regards,
Neil