Re: Slur position : "catching" Llilypond values...

[David Nalesnik]

On 2/14/11, Dmytro O. Redchuk <address@hidden> wrote:

> Would be great it if allows to specify which grob's positions to alter, like
> this:
>
> \offsetPositions #"Arpeggio" #'(-2 . 2)
>

Hi, Dmytro --

I actually have been working on a snippet which generalizes another
function -- namely, the oft-cited snippet for applying 'extra-offset
to broken slurs.

http://www.lilypond.org/doc/v2.12/Documentation/user/lilypond/Difficult-tweaks#Difficult-tweaks

It should be easy to do a similar thing with the positions snippet.

Here is my function:

offsetBrokenSpanner =
#(define-music-function (parser location name offsets) (string? pair?)
    #{
      \overrideProperty $name #'after-line-breaking #(broken-spanner $offsets)
    #}
)

#(define ((broken-spanner offsets) grob)
  (let* (
         ; have we been split?
         (orig (ly:grob-original grob))

         ; if yes, get the split pieces (our siblings)
         (siblings (if (ly:grob? orig)
                     (ly:spanner-broken-into orig) '() )))

   (if (and (>= (length siblings) 2)
             (eq? (car (last-pair siblings)) grob))
     (ly:grob-set-property! grob 'extra-offset offsets))))


To modify a slur:

\offsetBrokenSpanner #"Slur" #'(x . y)

To modify a grob in a higher context:

\offsetBrokenSpanner #"Staff.OttavaBracket" #'(x . y)

My only hesitation is this statement in the NR (section referenced above):

"When applying this trick, the new after-line-breaking callback should
also call the old one after-line-breaking, if there is one. For
example, if using this with Hairpin, ly:hairpin::after-line-breaking
should also be called."

I confess I don't fully understand this, and hence I'm unsure if my
function is overly simplifed.  However, calling \offsetBrokenSpanner
#"Hairpin" #'(x . y) seems to work as expected.

[Note: the issue of contexts is why I used \overrideProperty instead
of \override.  For some reason, \override will not accept
"Staff.OttavaBracket" as a valid grob name.  I wonder if there is any
drawback to using \overrideProperty, since I've seen it so
infrequently.]

Best,
David