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4.3.4 Kontextusok tulajdonságainak módosítása

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 the 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.

propertyName	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	"Cello I"
fontSize	Real	Increase or decrease the font size	2.4
stanza	Text	Set the text to print before the start of a verse	"2"

where a Boolean is either True (#t) or False (#f), an Integer is a positive whole number, a Real is a positive or negative decimal number, and text is enclosed in double apostrophes. Note the occurrence of hash signs, (#), in two different places – as part of the Boolean value before the t or f, and before value in the \set statement. So when a Boolean is being entered you need to code two hash signs, e.g., ##t.

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 instrumentName clearly lives in the Staff context, since it is the staff that is to be named. In this example the first staff is labeled, but not the second, because we omitted the context name.

<<
  \new Staff \relative {
    \set Staff.instrumentName = "Soprano"
    c''4 c
 }
  \new Staff \relative {
  \set instrumentName = "Alto"  % Wrong!
  d'4 d
 }
>>

Remember the default context name is Voice, so the second \set command set the property instrumentName in the Voice context to „Alto”, 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 logged in the log file.

Similarly, if the property name is mis-spelt no error message is produced, and clearly the expected action cannot be performed. In fact, you can set any (fictitious) ‘property’ using any name you like in any context that exists by using the \set command. But if the name is not known to LilyPond it will not cause any action to be taken. Some text editors with special support for LilyPond input files document property names with bullets when you hover them with the mouse, like JEdit with LilyPondTool, or highlight unknown property names differently, like ConTEXT. If you do not use an editor with such features, it is recommended to check the property name in the Internals Reference: see Tunable context properties, or Contexts.

The instrumentName 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 {
    ais'4 aes
  }
  \new Staff \relative {
    \set Staff.extraNatural = ##f
    ais'4 aes
  }
>>

and this turns them off in all staves:

<<
  \new Staff \relative {
    ais'4 aes
  }
  \new Staff \relative {
    \set Score.extraNatural = ##f
    ais'4 aes
  }
>>

As another example, if clefTransposition is set in the Score context this immediately changes the value of the octavation 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.

c4
% make note heads smaller
\set fontSize = #-4
d e
% make note heads larger
\set fontSize = #2.5
f g
% return to default size
\unset fontSize
a b

We have now seen how to set the values of several different types of property. Note that integers and numbers are always preceded by a hash sign, #, while a true or false value is specified by ##t and ##f, 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 {
    gis' ges aes ais
  }
  \new Staff \with { extraNatural = ##f }
  \relative {
    gis' ges aes ais
  }
>>

Or, if the property override is to be applied to all staves within the score, it may be appended to an explicit \new Score command, like this:

\score {
  \new Score \with { extraNatural = ##f } <<
    \new Staff {
      \relative {
        gis' ges aes ais
      }
    }
    \new Staff {
      \relative {
        gis' ges aes ais
      }
    }
  >>
}

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 a example to show the format:

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

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.

Lásd még

A kottaírás kézikönyve: Changing context default settings, The set command.

Internals Reference: Contexts, Tunable context properties.

---

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