LilyPond Beginnershandleiding

Hoofdstuk 4: Tweaking output 88
4 Tweaking output
This chapter discusses how to modify output. LilyPond is extremely configurable; virtually every
fragment of output may be changed.
4.1 Tweaking basics
4.1.1 Introduction to tweaks
‘Tweaking’ is a LilyPond term for the various methods available to the user for modifying
the actions taken during interpretation of the input file and modifying the appearance of the
printed output. Some tweaks are very easy to use; others are more complex. But taken together
the methods available for tweaking permit almost any desired appearance of the printed music
to be achieved.
In this section we cover the basic concepts required to understand tweaking. Later we give a
variety of ready-made commands which can simply be copied to obtain the same effect in your
own scores, and at the same time we show how these commands may be constructed so that you
may learn how to develop your own tweaks.
Before starting on this Chapter you may wish to review the section Sectie 3.3 [Contexts and
engravers], pagina 59, as Contexts, Engravers, and the Properties contained within them are
fundamental to understanding and constructing Tweaks.
4.1.2 Objects and interfaces
Tweaking involves modifying the internal operation and structures of the LilyPond program, so
we must first introduce some terms which are used to describe those internal operations and
structures.
The term ‘Object’ is a generic term used to refer to the multitude of internal structures
built by LilyPond during the processing of an input file. So when a command like \new Staff
is encountered a new object of type Staff is constructed. That Staff object then holds all the
properties associated with that particular staff, for example, its name and its key signature,
together with details of the engravers which have been assigned to operate within that staff’s
context. Similarly, there are objects to hold the properties of all other contexts, such as Voice
objects, Score objects, Lyrics objects, as well as objects to represent all notational elements
such as bar lines, note heads, ties, dynamics, etc. Every object has its own set of property values.
Some types of object are given special names. Objects which represent items of notation on
the printed output such as note heads, stems, slurs, ties, fingering, clefs, etc are called ‘Layout
objects’, often known as ‘Graphical Objects’, or ‘Grobs’ for short. These are still objects in the
generic sense above, and so they too all have properties associated with them, such as their
position, size, color, etc.
Some layout objects are still more specialized. Phrasing slurs, crescendo hairpins, ottava
marks, and many other grobs are not localized in a single place – they have a starting point, an
ending point, and maybe other properties concerned with their shape. Objects with an extended
shape like these are called ‘Spanners’.
It remains to explain what ‘Interfaces’ are. Many objects, even though they are quite different,
share common features which need to be processed in the same way. For example, all grobs
have a color, a size, a position, etc, and all these properties are processed in the same way
during LilyPond’s interpretation of the input file. To simplify these internal operations these
common actions and properties are grouped together in an object called a grob-interface.
There are many other groupings of common properties like this, each one given a name ending
in interface. In total there are over 100 such interfaces. We shall see later why this is of interest
and use to the user.