9.1.6 Defining new contexts

Specific contexts, like Staff and Voice, are made of simple building blocks, and it is possible to compose engraver plug-ins in different combinations, thereby creating new types of contexts.

The next example shows how to build a different type of Voice context from scratch. It will be similar to Voice, but prints centered slash noteheads only. It can be used to indicate improvisation in Jazz pieces,

These settings are again done within a \context block inside a \layout block,

\layout {
  \context {
    ...
  }
}

In the following discussion, the example input shown should go on the ... in the previous fragment.

First, the context gets a name. Instead of Voice it will be called ImproVoice ,

\name ImproVoice

Since it is similar to the Voice , we want commands that work on (existing) Voice s to remain working. This is achieved by giving the new context an alias Voice ,

\alias Voice

The context will print notes, and instructive texts

\consists Note_heads_engraver
\consists Text_engraver

but only on the center line,

\consists Pitch_squash_engraver
squashedPosition = #0

The Pitch_squash_engraver modifies note heads (created by Note_heads_engraver) and sets their vertical position to the value of squashedPosition, in this case 0, the center line.

The notes look like a slash, without a stem,

\override NoteHead #'style = #'slash
\override Stem #'transparent = ##t

All these plug-ins have to cooperate, and this is achieved with a special plug-in, which must be marked with the keyword \type. This should always be Engraver_group_engraver,

\type "Engraver_group_engraver"

Put together, we get

\context {
  \name ImproVoice
  \type "Engraver_group_engraver"
  \consists "Note_heads_engraver"
  \consists "Text_engraver"
  \consists Pitch_squash_engraver
  squashedPosition = #0
  \override NoteHead #'style = #'slash
  \override Stem #'transparent = ##t
  \alias Voice
}

Contexts form hierarchies. We want to hang the ImproVoice under Staff , just like normal Voices. Therefore, we modify the Staff definition with the \accepts command,¹

\context {
  \Staff
  \accepts ImproVoice
}

Putting both into a \layout block, like

\layout {
  \context {
    \name ImproVoice
    ...
  }
  \context {
    \Staff
    \accepts "ImproVoice"
  }
}

Then the output at the start of this subsection can be entered as

\relative c'' {
  a4 d8 bes8
  \new ImproVoice {
    c4^"ad lib" c
    c4 c^"undress"
    c c_"while playing :)"
  }
  a1
}

Other languages: English.
Using automatic language selection.