5.2.2 Properties found in interfaces

Suppose now that we wish to print the lyrics in italics. What form of \override command do we need to do this? We first look in the IR page listing ‘All layout objects’, as before, and look for an object that might control lyrics. We find LyricText, which looks right. Clicking on this shows the settable properties for lyric text. These include the font-series and font-size, but nothing that might give an italic shape. This is because the shape property is one that is common to all font objects, so, rather than including it in every layout object, it is grouped together with other similar common properties and placed in an Interface, the font-interface.

So now we need to learn how to find the properties of interfaces, and to discover what objects use these interface properties.

Look again at the IR page that describes LyricText. At the bottom of the page is a list of clickable interfaces that LyricText supports. The list has several items, including font-interface. Clicking on this brings up the properties associated with this interface, which are also properties of all the objects which support it, including LyricText.

Now we see all the user-settable properties which control fonts, including ‘font-shape (symbol)’. The value in parentheses gives the variable type expected by the property; here it is a (Scheme) symbol. The IR also documents the possible values, which are upright, italics, or slanted.

You will notice that font-series and font-size are also listed there. This immediately raises the question: Why are the common font properties font-series and font-size listed under LyricText as well as under the interface font-interface but font-shape is not? The answer is that font-series and font-size are changed from their global default values when a LyricText object is created, but font-shape is not. The entries in LyricText then tell you the values for those two properties which apply to LyricText. Other objects which support font-interface will set these properties differently when they are created.

Let’s see if we can now construct the \override command to change the lyrics to italics. The object is LyricText, the property is font-shape and the value is italic. As before, we’ll omit the context.

As an aside, although it is an important one, note that some properties take values that are symbols, like italic, and must be preceded by an apostrophe, ‘'’. Symbols are then read internally by LilyPond. Note the distinction from arbitrary text strings, which would appear as "a text string"; for more details about symbols and strings, see Scheme tutorial.

So we see that the \override command needed to print the lyrics in italics is:

\override LyricText.font-shape = #'italic

This should be placed just in front of the lyrics we wish to affect, like so:

{
  \key es \major
  \time 6/8
  \relative {
    r4 bes'8 bes[( g]) g |
    g8[( es]) es d[( f]) as |
    as8 g
  }
  \addlyrics {
    \override LyricText.font-shape = #'italic
    The man who | feels love's sweet e -- | mo -- tion
  }
}

and the lyrics are all printed in italics.

参见

Extending: Scheme tutorial.