\version "2.13.32"

#(define (dynamic-align-engraver context)
   (let ((line '())
         (ended '())
         (started '())
         (scripts '())
         (support '())
         (running '())
         (early-end #f))
     
     `((acknowledgers
        (dynamic-interface
         . ,(lambda (engraver grob source-engraver)
              (if (null? line)
                  (set! line
                        (ly:engraver-make-grob engraver 'DynamicLineSpanner
                                               (event-cause grob))))

              (cond ((ly:spanner? grob)
                     (set! started (cons grob started))
                     (if (and (grob::has-interface grob 'dynamic-text-spanner-interface)
                              (eq? (ly:grob-property grob 'style) 'none))
                         (set! early-end #t)))

                    ((ly:item? grob)
                     (set! scripts (cons grob scripts)))
                    (else
                     (ly:programming-error "Unknown dynamic grob: ~a" grob)))

              (ly:axis-group-interface::add-element line grob)

              (if (ly:stream-event? (event-cause grob))
                  (let ((dir (ly:event-property (event-cause grob) 'direction)))
                    (and (ly:dir? dir)
                         (set! (ly:grob-property line 'direction) dir))))))

        (note-column-interface
         . ,(lambda (engraver grob source-engraver)
              (set! support (cons grob support)))))

       (end-acknowledgers
        (dynamic-interface
         . ,(lambda (engraver grob source-engraver)
              (if (ly:spanner? grob)
                  (set! ended (cons grob ended))))))

       (listeners
        (break-dynamic-span-event . ,(lambda (trans ev)
                                       (set! early-end #t))))

       (stop-translation-timestep
        . ,(lambda (engraver)
             (set! running (append running started))

             (and (pair? ended)
                  (for-each (lambda (x)
                              (if (member x running)
                                  (set! running (delete x running))
                                  (ly:programming-error "Lost track of this dynamic spanner.")))
                            ended))

             (let ((end (and (ly:grob? line)
                             (or (null? running)
                                 early-end))))

               (for-each (lambda (dir)                     
                           (and (ly:grob? line)
                                (or
                                 (and (= dir LEFT)
                                      (null? (ly:spanner-bound line LEFT)))
                                 (and end
                                      (= dir RIGHT)
                                      (null? (ly:spanner-bound line RIGHT))))
                                (let ((spanners (if (= dir LEFT)
                                                    started
                                                    ended))
                                      (bound #f))

                                  (cond ((pair? scripts)
                                         (set! bound (car scripts)))
                                        ((pair? spanners)
                                         (set! bound (ly:spanner-bound (car spanners) dir)))
                                        (else
                                         (if (not early-end)
                                             (ly:programming-error "Started DynamicLineSpanner but have no left bound."))
                                         (set! bound (ly:context-property context 'currentMusicalColumn))))
                                  (ly:spanner-set-bound! line dir bound))))
                         (list LEFT RIGHT))

               (and (ly:grob? line)
                    (pair? support)
                    (for-each (lambda (col)
                                (ly:pointer-group-interface::add-grob line 'side-support-elements col))
                              support))

               (if end
                   (set! line '()))

               (set! ended '())
               (set! started '())
               (set! scripts '())
               (set! support '())))))))

\layout {
  \context {
    \Voice
    \remove Dynamic_align_engraver
    \consists #dynamic-align-engraver
  }
}

\relative c' {
  c4\< d e f
  g1\!^\ff
  \dimTextDim
  g1\>
  a1
  b1
  a,1\!\p

  c4\< d e f \breakDynamicSpan
  g1\!^\ff
  \override DynamicTextSpanner #'style = #'none
  \dimTextDim
  g1\>
  a1
  b1
  a,4\!\p
}