%% Generated by lilypond-book.py
%% Options: [indent=0\mm,line-width=160\mm]
\include "lilypond-book-preamble.ly"


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% Start cut-&-pastable-section
% ****************************************************************



\paper {
  indent = 0\mm
  line-width = 160\mm
  force-assignment = #""
  line-width = #(- line-width (* mm  3.000000))
}

\layout {
  
}





% ****************************************************************
% ly snippet:
% ****************************************************************
\sourcefilename "centering-markup-on-note-heads-automatically.ly"
\sourcefileline 0
% DO NOT EDIT this file manually; it is automatically
% generated from Documentation/snippets/new
% Make any changes in Documentation/snippets/new/
% and then run scripts/auxiliar/makelsr.py
%
% This file is in the public domain.
%% Note: this file works from version 2.14.0
\version "2.14.0"

\header {
  lsrtags = "text, tweaks-and-overrides, contexts-and-engravers"
  texidoc = "
For technical reasons, text scripts attached to note heads cannot
easily be centered on a note head's width, unlike articulations.

Instead of using trial-and-error offset tweaks, this snippet uses a
Scheme engraver to reset the horizontal parent of each markup to a
@code{NoteColumn}.  This also allows text to follow note heads which have
been shifted via @code{force-hshift}.
"
  doctitle = "Centering markup on note heads automatically"
} % begin verbatim


#(define (Text_align_engraver ctx)
  (let ((scripts '())
        (note-column #f))

    `((acknowledgers
       (note-column-interface
        . ,(lambda (trans grob source)
             ;; cache NoteColumn in this Voice context
             (set! note-column grob)))

       (text-script-interface
        . ,(lambda (trans grob source)
             ;; whenever a TextScript is acknowledged,
             ;; add it to `scripts' list
             (set! scripts (cons grob scripts)))))

      (stop-translation-timestep
       . ,(lambda (trans)
            ;; if any TextScript grobs exist,
            ;; set NoteColumn as X-parent
            (and (pair? scripts)
                 (for-each (lambda (script)
                             (set! (ly:grob-parent script X) note-column))
                           scripts))
            ;; clear scripts ready for next timestep
            (set! scripts '()))))))

\layout {
  \context {
    \Voice
    \consists #Text_align_engraver
    \override TextScript #'X-offset =
      #ly:self-alignment-interface::aligned-on-x-parent
    \override TextScript #'self-alignment-X = #CENTER
  }
}

\new Staff <<
  \relative c'' {
    \override NoteColumn #'force-hshift = #3
    c1-\markup { \arrow-head #Y #DOWN ##t }
  }
  \\
  \relative c' {
    a4 a-\markup { \huge ^ } a a
  }
>>



% ****************************************************************
% end ly snippet
% ****************************************************************