Re: missing glissando features (bugs?)

[Neil Puttock]

2009/5/9 Marc Hohl <address@hidden>:

> I tried to receive the informations needed by overriding the Glissando
> #'stencil with
> a function which simply displays the values obtained by the ly:spanner-bound
> call
> before calling ly:line-spanner::print, but I get only  #<Grob NoteHead > on
> the terminal.
>
> What am I doing wrong here?

Nothing, though to be on the safe side, it's best to ensure you're
dealing with the unbroken spanner by using ly:grob-original: if a user
decides to have a glissando over a line break, it won't be possible to
get noteheads for both bounds.

Once you have the NoteHead grobs, you can retrieve their pitches from
the events which created them:

\relative c' {
  \override NoteHead #'stencil = #(lambda (grob)
     ;; event-cause is a convenient shorthand in this case for
(ly:grob-property grob 'cause)
     (display (event-cause grob))
     (ly:note-head::print grob))
     c4
}

>>

#<Prob: Stream_event C++: Stream_event((music-cause . #<Prob: Music
C++: Music((length . #<Mom 1/4>) (elements) (duration . #<Duration 4
>) (pitch . #<Pitch c' >) (origin . #<location
/home/neil/Documents/test.ly:254:5>))((display-methods #<procedure #f
(note parser)>) (name . NoteEvent) (types general-music event
note-event rhythmic-event melodic-event)) >
) (length . #<Mom 1/4>) (elements) (duration . #<Duration 4 >) (pitch
. #<Pitch c' >) (origin . #<location
/home/neil/Documents/test.ly:254:5>))((class . note-event)) >

>From the event, you can get the pitch using ly:event-property event 'pitch.

Putting it all together:

#(define (glissando::calc-extra-dy grob)
   (let* ((original (ly:grob-original grob))
          (left-bound (ly:spanner-bound original LEFT))
          (right-bound (ly:spanner-bound original RIGHT))
          (left-pitch (ly:event-property (event-cause left-bound) 'pitch))
          (right-pitch (ly:event-property (event-cause right-bound) 'pitch)))

     ;; work out return value based on pitches here

     0))

Regards,
Neil