Documentation/snippets/new/using-ly-grob-object-to-access-grobs-with--tweak.ly

   1 \version "2.13.10"
   2
   3 \header {
   4   lsrtags = "tweaks-and-overrides"
   5
   6   texidoc = "
   7 Some grobs can be accessed @qq{laterally} from within another grob's
   8 callback.  These are usually listed as @qq{layout objects} in the
   9 @qq{Internal properties} section of a grob-interface.  The function
  10 @code{ly:grob-object} is used to access these grobs.
  11
  12
  13 Demonstrated below are some ways of accessing grobs from within a
  14 NoteHead callback, but the technique is not limited to NoteHeads.
  15 However, the NoteHead callback is particularly important, since it is
  16 the implicit callback used by the @code{\\tweak} command.
  17
  18
  19 The example function defined below (\"display-grobs\") is probably not
  20 that useful, but it demonstrates that the grobs are indeed being
  21 accessed.
  22
  23
  24 Example console output:
  25
  26
  27 @example
  28 --------------------
  29 #-Grob Accidental -
  30 #-Grob Arpeggio -
  31 #-Grob Stem -
  32 @end example
  33
  34
  35 "
  36   doctitle = "Using ly:grob-object to access grobs with \\tweak"
  37 }
  38
  39 #(define (notehead-get-accidental notehead)
  40    ;; notehead is grob
  41    (ly:grob-object notehead 'accidental-grob))
  42
  43 #(define (notehead-get-arpeggio notehead)
  44    ;; notehead is grob
  45    (let ((notecolumn (notehead-get-notecolumn notehead)))
  46      (ly:grob-object notecolumn 'arpeggio)))
  47
  48 #(define (notehead-get-notecolumn notehead)
  49    ;; notehead is grob
  50    (ly:grob-parent notehead X))
  51
  52 #(define (notehead-get-stem notehead)
  53    ;; notehead is grob
  54    (let ((notecolumn (notehead-get-notecolumn notehead)))
  55      (ly:grob-object notecolumn 'stem)))
  56
  57 #(define (display-grobs notehead)
  58    ;; notehead is grob
  59    (let ((accidental (notehead-get-accidental notehead))
  60          (arpeggio (notehead-get-arpeggio notehead))
  61          (stem (notehead-get-stem notehead)))
  62      (format #t "~2&~a\n" (make-string 20 #\-))
  63      (for-each
  64       (lambda (x) (format #t "~a\n" x))
  65       (list accidental arpeggio stem))))
  66
  67 \relative c' {
  68   %% display grobs for each note head:
  69   %\override NoteHead #'before-line-breaking = #display-grobs
  70   <c
  71   %% or just for one:
  72   \tweak #'before-line-breaking #display-grobs
  73   es
  74   g>1\arpeggio
  75 }