Re: extending event-listener.ly

[Graham Percival]

On Mon, Mar 25, 2013 at 08:58:09AM -0300, luis jure wrote:
> i looked at event-listener.ly, but i'm afraid it's way over my head. i can
> hardly manage some basic python, for me scheme is undecipherable. 
> 
> could anyone give me a hint how to modify event-listener.ly to recognize
> parenthesized notes?

Unfortunately you'll need some scheme knowledge, but if you can
get the general idea of the below function then you should be
fine:

#(define (format-note engraver event)
   (let* ((origin (ly:input-file-line-char-column
                   (ly:event-property event 'origin))))
     (print-line engraver
                 "note"
                 ;; get a MIDI pitch value.
                 (+ 60 (ly:pitch-semitones
                        (ly:event-property event 'pitch)))
                 (ly:duration->string
                  (ly:event-property event 'duration))
                 (format-moment (ly:duration-length
                                 (ly:event-property event
'duration)))
                 ;; point and click info
                 (ly:format "point-and-click ~a ~a"
                            (caddr origin)
                            (cadr origin)))))

The important bit is the (print-line ...) function.  It has a
number of arguments:
  - engraver
  - "note"
  - a MIDI pitch value
  - a duration (like "4.")
  - a duration (like "1.25")
  - point-and-click info

To add \parenthesize, you need to create a similar function or
extend that original one to deal with those events.  To see the
events, try:

\displayMusic { c'4 \parenthesize d' e }

oh, it looks like \parenthesize is an option to a note, rather
than a separate event:
...
        (make-music
          'NoteEvent
          'parenthesize
          #t
          'duration
          (ly:make-duration 2 0 1)
          'pitch
          (ly:make-pitch 0 1 0))
...


In that case, you need to add another argument to the
(print-line...) function to indicate whether the note is
parenthesized or not.  That requires a bunch more scheme, but this
should be enough hints for you to start reading the lilypond
scheme tutorial and the Extending manual.

A simple binary field would be enough for your personal use, but
it would be nice to have a more general approach in case people
want to add more options for notes.  Don't worry about this
general approach (required for accepted patches into mainstream
lilypond) right now; first just get the basics working for your
particular purpose.

- Graham