doc/snippets/meter-equivalences.ly

   1 \version "2.19"
   2
   3 \header {
   4   texidoc = "When switching between time signatures, it is
   5 often advisable to explicitly indicate a beat equivalence
   6 between two written durations."
   7
   8   tagline = ##f
   9 }
  10
  11 \paper {
  12   #(set-paper-size "a6")
  13 }
  14
  15 #(use-modules (ice-9 regex))
  16
  17 equiv =
  18 #(define-music-function (str) (string?)
  19
  20    (define (parse-my-duration duration-string)
  21   "Parse the `duration-string', e.g. ''4..'' or ''breve.'',
  22 and return a (log dots) list.
  23   Unlike the original `parse-simple-duration',
  24 this function is whitespace-insensitive."
  25   (let* ((duration-string (string-trim-both duration-string))
  26          (match (regexp-exec (make-regexp "(breve|longa|maxima|[0-9]+)(\\.*)")
  27                              duration-string)))
  28     (if (and match (string=? duration-string (match:substring match 0)))
  29         (let ((len (match:substring match 1))
  30               (dots (match:substring match 2)))
  31           (list (cond ((string=? len "breve") -1)
  32                       ((string=? len "longa") -2)
  33                       ((string=? len "maxima") -3)
  34                       (else (log2 (string->number len))))
  35                 (if dots (string-length dots) 0)))
  36         (ly:error (_ "not a valid duration string: ~a") duration-string))))
  37
  38    (let* ((mark-ev (make-music 'MarkEvent))
  39           (mark-ch (make-event-chord (list mark-ev)))
  40           (equiv-lst (string-split str #\= ))
  41           (before (parse-my-duration (car equiv-lst)))
  42           (after (parse-my-duration (cadr equiv-lst)))
  43           (before-mark (make-note-by-number-markup (car before) (cadr before) 1))
  44           (after-mark (make-note-by-number-markup (car after) (cadr after) 1))
  45           (equiv-mark
  46             (make-concat-markup
  47               (list
  48                 (make-general-align-markup Y DOWN
  49                   (make-smaller-markup before-mark))
  50                 (make-simple-markup " ")
  51                 (make-simple-markup "=")
  52                 (make-simple-markup " ")
  53                 (make-general-align-markup Y DOWN
  54                   (make-smaller-markup after-mark))
  55                 )))
  56           (mark-set (context-spec-music
  57               (make-property-set 'rehearsalMark equiv-mark)
  58               'Score)))
  59          (ly:music-set-property! mark-ev 'origin (*location*))
  60          (ly:music-set-property! mark-ev 'label equiv-mark)
  61          mark-ch))
  62
  63 \relative c' {
  64   \time 6/8
  65   d8 e f e d e |
  66   \time 3/4
  67   \equiv "8 = 8"
  68   g4 g g
  69 }
  70