centering note columns [WAS: Directional NoteHead Stencil Support]

[David Nalesnik]

Hi,

In a recent thread, the topic of centering items within their measures came up.  This post on "Scores of Beauty" ( http://lilypondblog.org/2013/06/horizontally-aligning-full-measure-rests/ )

shows an example where this nonstandard practice looks much better.  Normally, of course, a note filling a measure isn't centered, while a whole rest is.  When the two occur at the same time, it's more appealing when both are centered.

(See also the thread at http://www.mail-archive.com/lilypond-user%40gnu.org/msg98447.html for a usage case.)

The Scores of Beauty post comes with a code attachment which allows automation of the process.

It just occurred to me that this might be done through PaperColumns.  Moving a PaperColumn will carry everything associated with it--the NoteColumn, noteheads, dots, stem, articulations.  And _arpeggio_ (which presented a difficulty discussed in the thread this branched off from).

Here is a sketch of that approach.  It doesn't yet allow for the fine-grained control of the other code.

Note: measures aren't resized.  We simply use the available space.  However... one of the nice features of paper columns is that there is easy access to adjoining paper columns.  I wonder if it's possible to manipulate their X-extents to create a more flexible approach?

--David

%%%%%%

\version "2.19.17"

\paper {

  right-margin = 3\in

}

#(define center-column

   (lambda (grob)

     (if (grob::has-interface grob 'note-column-interface)

         (let* ((col (ly:item-get-column grob))

                (left-col (ly:grob-object col 'left-neighbor))

                (right-col (ly:grob-object col 'right-neighbor)))

           ;; we only shift a PaperColumn if it is alone in its

           ;; measure

           (if (and (ly:grob-property left-col 'non-musical)

                    (ly:grob-property right-col 'non-musical))

               (let* ((sys (ly:grob-system grob))

                      (col-center (interval-center

                                   (ly:grob-extent col sys X)))

                      (left-right-X

                       (cdr (ly:grob-extent left-col sys X)))

                      (right-left-X

                       (car (ly:grob-extent right-col sys X)))

                      (middle-X

                       (- (average left-right-X right-left-X)

                         col-center)))

                 (ly:grob-translate-axis! col middle-X X))))

         ;; do nothing if override applied to something other

         ;; than NoteColumn

         '()

         )))

%%%%%%%%%%%%%%

\new PianoStaff <<

  \new Staff {

    <c' e' g' c''>1\accent\fermata\f\arpeggio

    c'4 d' e' f'

    R1

  }

  \new Staff {

    R1

    R1

    <c' e' g' c''>1\accent\fermata\f\arpeggio

  }

>>

\layout {

  ragged-right = ##f

  \context {

    \Voice

    \override NoteColumn.after-line-breaking = #center-column

  }

}