4.3.4 Modifying context properties

Contexts are responsible for holding the values of a number of context properties. Many of them can be changed to influence the interpretation of the input and so change the appearance of the output. They are changed by the \set command. This takes the form

\set ContextName.propertyName = value

where ContextName is usually Score, Staff, or Voice. It may be omitted, in which case the current context (typically Voice) is assumed.

The names of context properties consist of words joined together with no hyphens or underscores, all except the first having a capital letter. Here are a few examples of some commonly used ones. There are many more.

Property Name	Type	Function	Example Value
extraNatural	Boolean	If true, set extra natural signs before accidentals	##t, ##f
currentBarNumber	integer	Set the current bar number	50
doubleSlurs	Boolean	If true, print slurs both above and below notes	##t, ##f
instrumentName	text	Set the name to be placed at the start of the staff	\markup { ... }
fontSize	real	Increase or decrease the font size	2.4
stanza	text	Set the text to print before the start of a verse	"2"

In the above table, a Boolean is either #t (true) or #f (false), an integer is a whole number (usually positive), a real is a positive or negative decimal number, and text is string enclosed in doublequote characters. Note the use of an additional hash sign (‘#’), which must always be used if a Scheme expression follows.

Before we can set any of these properties we need to know in which context they operate. Sometimes this is obvious, but occasionally it can be tricky. If the wrong context is specified, no error message is produced, but the expected action will not take place. For example, the clefGlyph clearly lives in the Staff context, since it is the staff’s clef glyph that is to be changed. In this example the first staff’s clef is printed correctly, but not the second – which prints the default treble clef instead of the expected bass (or F) clef – because we omitted the context name.

<<
  \new Staff \relative {
    \set Staff.clefGlyph = "clefs.C"
    c''2 c
  }
  \new Staff \relative {
    \set clefGlyph = "clefs.F"  % Wrong!
    d'2 d
  }
>>

Remember the default context name is Voice, so the second \set command set the property clefGlyph in the Voice context to clefs.F, but as LilyPond does not look for any such property in the Voice context, no further action took place. This is not an error, and no error message is emitted.

The clefGlyph property will take effect only if it is set in the Staff context, but some properties can be set in more than one context. For example, the property extraNatural is by default set to #t (true) for all staves. If it is set to #f (false) in one particular Staff context it applies just to the accidentals on that staff. If it is set to false in the Score context it applies to all staves.

So this turns off extra naturals in one staff:

<<
  \new Staff \relative {
    aeses'2 aes
  }
  \new Staff \relative {
    \set Staff.extraNatural = ##f
    aeses'2 aes
  }
>>

and this turns them off in all staves:

<<
  \new Staff \relative {
    aeses'2 aes
  }
  \new Staff \relative {
    \set Score.extraNatural = ##f
    aeses'2 aes
  }
>>

As another example, if clefTransposition is set in the Score context this immediately changes the value of the transposition in all current staves and sets a new default value, which will be applied to all staves.

The opposite command, \unset, effectively removes the property from the context, which causes most properties to revert to their default value. Usually \unset is not required as a new \set command will achieve what is wanted.

The \set and \unset commands can appear anywhere in the input file and will take effect from the time they are encountered until the end of the score or until the property is \set or \unset again. Let’s try changing the font size, which affects the size of the note heads (among other things) several times. The change is from the default value, not the most recently set value.

\relative {
  c'4 d
  % make note heads smaller
  \set fontSize = -4
  e4 f |
  % make note heads larger
  \set fontSize = 2.5
  g4 a
  % return to default size
  \unset fontSize
  b4 c |
}

We have now seen how to set the values of several different types of properties. Note that Scheme expressions are introduced with a hash sign, ‘#’, so the ‘true’ and ‘false’ values are specified by ##t and ##f, respectively, with two hash signs. A text property should be enclosed in double quotation signs, as above, although we shall see later that text can actually be specified in a much more general way by using the very powerful \markup command.

Setting context properties with \with

The default value of context properties may be set at the time the context is created. Sometimes this is a clearer way of setting a property value if it is to remain fixed for the duration of the context. When a context is created with a \new command it may be followed immediately by a \with { … } block in which the default property values are set. For example, if we wish to suppress the printing of extra naturals for the duration of a staff we would write

\new Staff \with { extraNatural = ##f }

like this:

<<
  \new Staff {
    \relative {
      gisis'4 gis aeses aes
    }
  }
  \new Staff \with { extraNatural = ##f } {
    \relative {
      gisis'4 gis aeses aes
    }
  }
>>

Properties set in this way may still be changed dynamically using \set and returned to the default value set in the \with block with \unset.

So if the fontSize property is set in a \with clause it sets the default value of the font size. If it is later changed with \set, this new default value may be restored with the \unset fontSize command.

Setting context properties with \context

The values of context properties may be set in all contexts of a particular type, such as all Staff contexts, with a single command. The context type is identified by using its type name, like Staff, prefixed by a back-slash: \Staff. The statement which sets the property value is the same as that in a \with block, introduced above. It is placed in a \context block within a \layout block. Each \context block will affect all contexts of the type specified throughout the \score or \book block in which the \layout block appears. Here is an example to show the format:

\score {
  \new Staff {
    \relative {
      cisis''4 e d cis
    }
  }
  \layout {
    \context {
      \Staff
      extraNatural = ##t
    }
  }
}

If the property override is to be applied to all staves within the score:

\score {
  <<
    \new Staff {
      \relative {
        gisis'4 gis aeses aes
      }
    }
    \new Staff {
      \relative {
        gisis'4 gis aeses aes
      }
    }
  >>
  \layout {
    \context {
      \Score
      extraNatural = ##f
    }
  }
}

Context properties set in this way may be overridden for particular instances of contexts by statements in a \with block, and by \set commands embedded in music statements.

参见

Notation Reference: Changing context default settings, Set and unset.

Internals Reference: Contexts, Tunable context properties.