* Single-staff polyphony::
* Voice styles::
* Collision resolution::
+* Merging rests::
* Automatic part combining::
* Writing music in parallel::
@end menu
@end ignore
+@node Merging rests
+@unnumberedsubsubsec Merging rests
+
+When using multiple voices it is common to merge rests which occur in both
+parts. This can be accomplished using @code{Merge_rests_engraver}.
+
+@lilypond[quote,verbatim]
+voiceA = \relative { d''4 r d2 | R1 | }
+voiceB = \relative { fis'4 r g2 | R1 | }
+\score {
+ <<
+ \new Staff \with {
+ instrumentName = "unmerged"
+ }
+ <<
+ \new Voice { \voiceOne \voiceA }
+ \new Voice { \voiceTwo \voiceB }
+ >>
+ \new Staff \with {
+ instrumentName = "merged"
+ \consists #Merge_rests_engraver
+ }
+ <<
+ \new Voice { \voiceOne \voiceA }
+ \new Voice { \voiceTwo \voiceB }
+ >>
+ >>
+}
+@end lilypond
+
+Setting the context property @code{suspendRestMerging} to @code{##t} allows for
+turning off rest merging temporarily.
+
@node Automatic part combining
@unnumberedsubsubsec Automatic part combining
--- /dev/null
+\version "2.19.60"
+
+\header {
+ texidoc = "Test for merging rests in different voices."
+}
+
+\paper {
+ ragged-right = ##f
+}
+
+voiceA = \relative {
+ % no rest merges
+ c''4 r c c |
+
+ % does not combine differently written rests
+ c4 r r2 |
+
+ % all rests merged
+ r2^"Up" r4 r8 r16 r32 r64 r128 r |
+
+ % multi-measure rests are combined
+ R1^"Upper text" |
+
+ % compressed multi-measure rests are combined
+ R1*3 |
+
+ % combining between beams, slurs
+ c8[( r c]) r c16[( r c] r c[ r c]) r |
+
+ % combining in tuplets
+ \tuplet 3/2 { c8 r r } r4 \tuplet 3/2 { c4 r r } |
+
+ % accents on rest, dynamics still aligned
+ r4->\f\> r-. r r\! |
+
+ % Non-multimeasure whole rests merged at the correct vertical position
+ \time 8/4
+ r1 r1
+
+ % Ensure when suspending merging rests are in their usual positions
+ \time 4/4
+ \set Staff.suspendRestMerging = ##t
+ r4 r8
+ \set Staff.suspendRestMerging = ##f
+ r8 r2 |
+
+ % Don't merge pitched rests
+ c4\rest d\rest e\rest f\rest |
+}
+
+voiceB = \relative {
+ r2 c'4 r |
+ c4 r r r |
+ r2_"Down" r4 r8 r16 r32 r64 r128 r |
+ R1_"Lower text" |
+ R1*3 |
+ c8[( r c]) r c16[( r c] r c[ r c]) r |
+ \tuplet 3/2 { c8 r r } r4 \tuplet 3/2 { c4 r r } |
+ r4-> r-. r r |
+ r1 r1 |
+ r4 r8 r r2 |
+ r4 r r r |
+}
+
+voiceC = \relative {
+ s1*2 |
+ r2 r4 r8 r16 r32 r64 r128 r | % Combines rests from more than 2 voices
+}
+
+\score {
+ \new Staff \with {
+ \consists #Merge_rests_engraver
+ } <<
+ \compressFullBarRests
+ \new Voice { \voiceOne \voiceA }
+ \new Voice { \voiceTwo \voiceB }
+ \new Voice { \voiceThree \voiceC }
+ >>
+}
(properties-read . ())
(properties-written . ())
(description . "Connect cross-staff stems to the stems above in the system")))
+
+(define-public (Merge_rests_engraver context)
+"Engraver to merge rests in multiple voices on the same staff.
+
+This works by gathering all rests at a time step. If they are all of the same
+length and there are at least two they are moved to the correct location as
+if there were one voice."
+
+ (define (is-single-bar-rest? mmrest)
+ (eqv? (ly:grob-property mmrest 'measure-count) 1))
+
+ (define (is-whole-rest? rest)
+ (eqv? (ly:grob-property rest 'duration-log) 0))
+
+ (define (mmrest-offset mmrest)
+ "For single measures they should hang from the second line from the top
+ (offset of 1). For longer multimeasure rests they should be centered on the
+ middle line (offset of 0).
+ NOTE: For one-line staves full single measure rests should be positioned at
+ 0, but I don't anticipate this engraver's use in that case. No errors are
+ given in this case."
+ (if (is-single-bar-rest? mmrest) 1 0))
+
+ (define (rest-offset rest)
+ (if (is-whole-rest? rest) 1 0))
+
+ (define (rest-eqv rest-len-prop)
+ "Compare rests according the given property"
+ (define (rest-len rest) (ly:grob-property rest rest-len-prop))
+ (lambda (rest-a rest-b)
+ (eqv? (rest-len rest-a) (rest-len rest-b))))
+
+ (define (rests-all-unpitched rests)
+ "Returns true when all rests do not override the staff-position grob
+ property. When a rest has a position set we do not want to merge rests at
+ that position."
+ (every (lambda (rest) (null? (ly:grob-property rest 'staff-position))) rests))
+
+ (define (merge-mmrests rests)
+ "Move all multimeasure rests to the single voice location."
+ (if (all-equal rests (rest-eqv 'measure-count))
+ (merge-rests rests mmrest-offset)))
+
+ (define (merge-rests rests offset-function)
+ (let ((y-offset (offset-function (car rests))))
+ (for-each
+ (lambda (rest) (ly:grob-set-property! rest 'Y-offset y-offset))
+ rests))
+ (for-each
+ (lambda (rest) (ly:grob-set-property! rest 'transparent #t))
+ (cdr rests)))
+
+ (define has-one-or-less (lambda (lst) (or (null? lst) (null? (cdr lst)))))
+ (define has-at-least-two (lambda (lst) (not (has-one-or-less lst))))
+ (define (all-equal lst pred)
+ (or (has-one-or-less lst)
+ (and (pred (car lst) (cadr lst)) (all-equal (cdr lst) pred))))
+
+ (let ((curr-mmrests '())
+ (mmrests '())
+ (rests '()))
+ (make-engraver
+ ((start-translation-timestep translator)
+ (set! rests '())
+ (set! curr-mmrests '()))
+ (acknowledgers
+ ((rest-interface engraver grob source-engraver)
+ (cond
+ ((ly:context-property context 'suspendRestMerging #f)
+ #f)
+ ((grob::has-interface grob 'multi-measure-rest-interface)
+ (set! curr-mmrests (cons grob curr-mmrests)))
+ (else
+ (set! rests (cons grob rests))))))
+ ((stop-translation-timestep translator)
+ (if (and
+ (has-at-least-two rests)
+ (all-equal rests (rest-eqv 'duration-log))
+ (rests-all-unpitched rests))
+ (merge-rests rests rest-offset))
+ (if (has-at-least-two curr-mmrests)
+ (set! mmrests (cons curr-mmrests mmrests))))
+ ((finalize translator)
+ (for-each merge-mmrests mmrests)))))
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