Imported Upstream version 2.14.2

[lilypond.git] / Documentation / snippets / centering-markup-on-note-heads-automatically.ly

diff --git a/Documentation/snippets/centering-markup-on-note-heads-automatically.ly b/Documentation/snippets/centering-markup-on-note-heads-automatically.ly
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+% 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
+  }
+>>