version that you are working on. See TRANSLATION for details.
@end ignore
-@c \version "2.11.65"
+@c \version "2.12.0"
@node Changing defaults
@chapter Changing defaults
@menu
* Contexts explained::
* Creating contexts::
+* Keeping contexts alive::
* Modifying context plug-ins::
* Changing context default settings::
* Defining new contexts::
@end itemize
+@node Keeping contexts alive
+@subsection Keeping contexts alive
+
+@cindex contexts, keeping alive
+@cindex contexts, lifetime
+
+Contexts are usually terminated at the first musical moment in
+which they have nothing to do. So @code{Voice} contexts die as
+soon as they contain no events; @code{Staff} contexts die as soon
+as all the @code{Voice} contexts within them contain no events; etc.
+This can cause difficulties if earlier contexts which have died
+have to be referenced, for example, when changing staves with
+@code{\change} commands, associating lyrics with a voice with
+@code{\lyricsto} commands, or when adding further musical events to
+an earlier context.
+
+There is an exception to this general rule: just one of the
+@code{Voice} contexts in a @code{Staff} context or in a
+@code{<<...>>} construct will always persist to the end of the
+enclosing @code{Staff} context or @code{<<...>>} construct, even
+though there may be periods when it has nothing to do. The context
+to persist in this way will be the first one encountered in the
+first enclosed @code{@{...@}} construct, ignoring any in enclosed
+@code{<<...>>} constructs.
+
+Any context can be kept alive by ensuring it has something to do at
+every musical moment. @code{Staff} contexts are kept alive by
+ensuring one of their voices is kept alive. One way of doing this
+is to add spacer rests to a voice in parallel with the real music.
+These need to be added to every @code{Voice} context which needs to
+be kept alive. If several voices are to be used sporadically it is
+safest to keep them all alive rather than attempting to rely on the
+exceptions mentioned above.
+
+In the following example, both voice A and voice B are kept alive
+in this way for the duration of the piece:
+
+@lilypond[quote,verbatim]
+musicA = \relative c'' { d4 d d d }
+musicB = \relative c'' { g4 g g g }
+keepVoicesAlive = {
+ <<
+ \new Voice = "A" { s1*5 } % Keep Voice "A" alive for 5 bars
+ \new Voice = "B" { s1*5 } % Keep Voice "B" alive for 5 bars
+ >>
+}
+
+music = {
+ \context Voice = "A" {
+ \voiceOneStyle
+ \musicA
+ }
+ \context Voice = "B" {
+ \voiceTwoStyle
+ \musicB
+ }
+ \context Voice = "A" { \musicA }
+ \context Voice = "B" { \musicB }
+ \context Voice = "A" { \musicA }
+}
+
+\score {
+ \new Staff <<
+ \keepVoicesAlive
+ \music
+ >>
+}
+@end lilypond
+
+@cindex lyrics, aligning with sporadic melody
+
+The following example shows how a sporadic melody line with lyrics
+might be written using this approach. In a real situation the
+melody and accompaniment would consist of several different
+sections, of course.
+
+@lilypond[quote,verbatim]
+melody = \relative c'' { a4 a a a }
+accompaniment = \relative c' { d4 d d d }
+words = \lyricmode { These words fol -- low the mel -- o -- dy }
+\score {
+ <<
+ \new Staff = "music" {
+ <<
+ \new Voice = "melody" {
+ \voiceOne
+ s1*4 % Keep Voice "melody" alive for 4 bars
+ }
+ {
+ \new Voice = "accompaniment" {
+ \voiceTwo
+ \accompaniment
+ }
+ <<
+ \context Voice = "melody" { \melody }
+ \context Voice = "accompaniment" { \accompaniment }
+ >>
+ \context Voice = "accompaniment" { \accompaniment }
+ <<
+ \context Voice = "melody" { \melody }
+ \context Voice = "accompaniment" { \accompaniment }
+ >>
+ }
+ >>
+ }
+ \new Lyrics \with { alignAboveContext = #"music" }
+ \lyricsto "melody" { \words }
+ >>
+}
+@end lilypond
+
+An alternative way, which may be better in many circumstances, is
+to keep the melody line alive by simply including spacer notes to
+line it up correctly with the accompaniment:
+
+@lilypond[quote,verbatim]
+melody = \relative c'' {
+ s1 % skip a bar
+ a4 a a a
+ s1 % skip a bar
+ a4 a a a
+}
+accompaniment = \relative c' {
+ d4 d d d
+ d4 d d d
+ d4 d d d
+ d4 d d d
+}
+words = \lyricmode { These words fol -- low the mel -- o -- dy }
+
+\score {
+ <<
+ \new Staff = "music" {
+ <<
+ \new Voice = "melody" {
+ \voiceOne
+ \melody
+ }
+ \new Voice = "accompaniment" {
+ \voiceTwo
+ \accompaniment
+ }
+ >>
+ }
+ \new Lyrics \with { alignAboveContext = #"music" }
+ \lyricsto "melody" { \words }
+ >>
+}
+@end lilypond
+
@node Modifying context plug-ins
@subsection Modifying context plug-ins
\name ImproVoice
\type "Engraver_group"
\consists "Note_heads_engraver"
+ \consists "Rhythmic_column_engraver"
\consists "Text_engraver"
\consists Pitch_squash_engraver
squashedPosition = #0
to apply after the input file has been converted to a music stream.
This is often not the case, as many additional elements are inserted
into the music stream implicitly. For example, when a note which is
-not part of a chord is processed, Lilypond implicitly inserts a
+not part of a chord is processed, LilyPond implicitly inserts a
@code{ChordEvent} event before the note, so separating the tweak
from the note. However, if chord symbols are placed round the
tweak and the note, the @code{\tweak} command comes after the
projects / lilypond.git / blobdiff