applying a tweak or callback to an \after-ed grob

[Kieren MacMillan]

Hi all,

I’ve been using David K’s lovely \after function (which should, IMO, be 
polished up and rolled into the distro!) to great effect in my recent 
engravings.

However, I’m having difficulty figuring out how to apply tweaks to the grobs 
that are \after-ed.
For example, see the snippet included below.

Any hints would be appreciated.

Thanks,
Kieren.

________________________

%%%  SNIPPET BEGINS
\version "2.19"

\paper { ragged-right = ##f }

hairpinWithCenteredText =
#(define-music-function (parser location text) (markup?)
   #{
     \once \override Voice.Hairpin.after-line-breaking =
     #(lambda (grob)
        (let* ((stencil (ly:hairpin::print grob))
               (par-y (ly:grob-parent grob Y))
               (dir (ly:grob-property par-y 'direction))
               (new-stencil (ly:stencil-aligned-to
                             (ly:stencil-combine-at-edge
                              (ly:stencil-aligned-to stencil X CENTER)
                              Y dir
                              (ly:stencil-aligned-to (grob-interpret-markup 
grob text) X CENTER))
                             X LEFT))
               (staff-space (ly:output-def-lookup (ly:grob-layout grob) 
'staff-space))
               (staff-line-thickness
                (ly:output-def-lookup (ly:grob-layout grob) 'line-thickness))
               (grob-name (lambda (x) (assq-ref (ly:grob-property x 'meta) 
'name)))
               (par-x (ly:grob-parent grob X))
               (dyn-text (eq? (grob-name par-x) 'DynamicText ))
               (dyn-text-stencil-x-length
                (if dyn-text
                    (interval-length
                     (ly:stencil-extent (ly:grob-property par-x 'stencil) X))
                    0))
               (x-shift
                (if dyn-text
                    (-
                     (+ staff-space dyn-text-stencil-x-length)
                     (* 0.5 staff-line-thickness)) 0))
               (original (ly:grob-original grob))
               (pieces (if (ly:grob? original)
                           (ly:spanner-broken-into original)
                           '())))

          (ly:grob-set-property! grob 'Y-offset 0) ;; ensure correct alignment
          (ly:grob-set-property! grob 'stencil
            (ly:stencil-translate-axis
             (if (or (null? pieces)
                     (and (pair? pieces)
                          (eq? grob (car pieces))))
                 new-stencil
                 stencil)
             x-shift X))))
   #})

hairpinPoco = \hairpinWithCenteredText \markup { \italic poco }

after =
#(define-music-function (parser location t e m)
     (ly:duration? ly:music? ly:music?)
     #{
         \context Bottom <<
             #m
             { \skip $t <> -\tweak extra-spacing-width #empty-interval $e }
         >>
     #})

test = {
    \once \hairpinPoco g1\< g\!
    \once \hairpinPoco \after 2 \< g1 g\!
}

\score { \test }
%%%  SNIPPET ENDS
________________________________

Kieren MacMillan, composer
‣ website: www.kierenmacmillan.info
‣ email: address@hidden