* Documentation/user/changing-defaults.itely (Creating contexts):

[lilypond.git] / Documentation / user / changing-defaults.itely

@c -*-texinfo-*-
@node Changing defaults
@chapter Changing defaults


The purpose of LilyPond's design is to provide the finest output
quality as a default. Nevertheless, it may happen that you need to
change this default layout.  The layout is controlled through a large
number of proverbial ``knobs and switches.''  This chapter does not
list each and every knob. Rather, it outlines what groups of controls
are available and explains how to lookup which knob to use for a
certain effect.

The controls available for tuning are described in a separate
document, the @internalsref{Program reference} manual. This manual
lists all different variables, functions and options available in
LilyPond. It is written as a HTML document, which is available
@uref{http://lilypond.org/doc/Documentation/user/out-www/lilypond-internals/,on-line},
but is also included with the LilyPond documentation package.

There are three areas where the default settings may be changed:

@itemize @bullet
@item Output: changing the appearance of individual
  objects. For example, changing stem directions, or the location of
  subscripts.
  
@item Context: changing aspects of the translation from music events to
  notation. For example, giving each staff a separate time signature. 
  
@item Global layout: changing the appearance of the spacing, line
  breaks and page dimensions.
@end itemize

Then, there are separate systems for typesetting text (like
@emph{ritardando}) and selecting different fonts. This chapter also
discusses these.

Internally, LilyPond uses Scheme (a LISP dialect) to provide
infrastructure.  Overriding layout decisions in effect accesses the
program internals, so it is necessary to learn a (very small) subset
of Scheme. That is why this chapter starts with a short tutorial on
entering numbers, lists, strings and symbols in Scheme.


@menu
* Scheme tutorial::             
* Interpretation contexts::     
* Tuning output::               
* Fonts::                       
* Text markup::                 
* Global layout::               
* Output details::              
@end menu

@node Scheme tutorial
@section Scheme tutorial

@cindex Scheme
@cindex GUILE
@cindex Scheme, in-line code
@cindex accessing Scheme
@cindex evaluating Scheme
@cindex LISP

LilyPond uses the Scheme programming language, both as part of the
input syntax, and as internal mechanism to glue together modules of
the program. This section is a very brief overview of entering data in
Scheme.@footnote{If you want to know more about Scheme, see
@uref{http://www.schemers.org}.}

The most basic thing of a language is data: numbers, character
strings, lists, etc. Here is a list of data types that are relevant to
LilyPond input.

@table @asis
@item Booleans
  Boolean values are True or False. The Scheme for True is @code{#t}
  and False is @code{#f}.
@item Numbers
  Numbers are entered in the standard fashion,
  @code{1} is the (integer) number one, while @code{-1.5} is a
  floating point number (a non-integer number). 
@item Strings
  Strings are enclosed in double quotes,
  @example
    "this is a string"
  @end example

  Strings may span several lines
  @example
    "this
    is
    a string"
  @end example

  Quotation marks and newlines can also be added with so-called escape
  sequences. The string @code{a said "b"} is entered as
  @example
    "a said \"b\""
  @end example

  Newlines and backslashes are escaped with @code{\n} and @code{\\}
respectively.
@end table


In a music file, snippets of Scheme code are introduced with the hash
mark @code{#}. So, the previous examples translated in LilyPond are

@example
  ##t ##f 
  #1 #-1.5
  #"this is a string"
  #"this
  is
  a string"
@end example

For the rest of this section, we will assume that the data is entered
in a music file, so we add @code{#}s everywhere.

Scheme can be used to do calculations. It uses @emph{prefix}
syntax. Adding 1 and 2 is written as @code{(+ 1 2)} rather than the
traditional 1+2.

@lisp
  #(+ 1 2)
   @result{} #3 
@end lisp

The arrow @result{} shows that the result of evaluating @code{(+ 1 2)}
is @code{3}.  Calculations may be nested; the result of a function may
be used for another calculation.

@lisp
  #(+ 1 (* 3 4))
   @result{} #(+ 1 12) 
   @result{} #13
@end lisp

These calculations are examples of evaluations; an expression like
@code{(* 3 4)} is replaced by its value @code{12}. A similar thing
happens with variables. After defining a variable  

@example
  twelve = #12 
@end example

variables can also be used in expressions, here

@example
  twentyFour = #(* 2 twelve) 
@end example 

the number 24 is stored in the variable @code{twentyFour}.

The @emph{name} of a variable is also an expression, similar to a
number or a string. It is entered as

@example
  #'twentyFour
@end example

The quote mark @code{'} prevents Scheme interpreter from substituting
@code{24} for the @code{twentyFour}. Instead, we get the name
@code{twentyFour}.

This syntax will be used very frequently, since many of the layout
tweaks involve assigning (Scheme) values to internal variables, for
example

@example
  \override Stem #'thickness = #2.6
@end example

This instruction adjusts the appearance of stems. The value @code{2.6}
is put into a the @code{thickness} variable of a @code{Stem}
object. This makes stems almost twice as thick as their normal size.
To distinguish between variables defined in input files (like
@code{twentyFour} in the example above), and internal variables, we
will call the latter ``properties.'' So, the stem object has a
@code{thickness} property.

Two-dimensional offsets (X and Y coordinates) as well as object sizes
(intervals with a left and right point) are entered as @code{pairs}. A
pair@footnote{In Scheme terminology, the pair is called @code{cons},
and its two elements are called car and cdr respectively.}  is entered
as @code{(first . second)} and, like symbols, they must be quoted,

@example
  \override TextScript #'extra-offset = #'(1 . 2)  
@end example 

This assigns the pair (1, 2) to @code{extra-offset} variable of the
TextScript object. This moves the object 1 staff space to the right,
and 2 spaces up.

The two elements of a pair may be arbitrary values, for example

@example
  #'(1 . 2)
  #'(#t . #f)
  #'("blah-blah" . 3.14159265)
@end example

A list is entered by enclosing its elements in parentheses, and adding
a quote. For example,
@example
  #'(1 2 3)
  #'(1 2 "string" #f)
@end example

We have been using lists all along.  A calculation, like @code{(+ 1
2)} is also a list (containing the symbol @code{+} and the numbers 1
and 2). Normally lists are interpreted as calculations, and the Scheme
interpreter substitutes the outcome of the calculation. To enter a
list, we stop evaluation. This is done by quoting the list with a
quote @code{'} symbol.  For calculations, do not use a quote.

Inside a quoted list or pair, there is no need to quote anymore.  The
following is a pair of symbols, a list of symbols and a list of lists
respectively,

@example
  #'(stem . head)
  #'(staff clef key-signature)
  #'((1) (2))
@end example


@node Interpretation contexts
@section Interpretation contexts

When music is printed, a lot of notation elements must be added to the
input, which is often bare bones.  For example, compare the input and
output of the following example:

@lilypond[verbatim,relative=2]
  cis4 cis2. g4
@end lilypond

The input is rather sparse, but in the output, bar lines, accidentals,
clef, and time signature are added. LilyPond @emph{interprets} the
input. During this step, the musical information is inspected in time
order, similar to reading a score from left to right. While reading,
the program remembers where measure boundaries are, and what pitches
need explicit accidentals.  This information can be presented on
several levels.  For example, the effect of an accidental is limited
to a single stave, while a bar line must be synchronized across the
entire score.

Within LilyPond, these rules and bits of information are grouped in
so-called Contexts. Examples of context are @context{Voice},
@context{Staff}, and @context{Score}.  They are hierarchical, for
example, a @context{Staff} can contain many @context{Voice}s, and a
@context{Score} can contain many @context{Staff} contexts.

Each context has the responsibility for enforcing some notation rules,
creating some notation objects and maintaining the associated
properties.  So, the synchronization of bar lines is handled at
@context{Score} context.  The @context{Voice} may introduce an
accidentals and then the @context{Staff} context maintains the rule to
show or suppress the accidental for the remainder of the measure.

For simple scores, contexts are created implicitly, and you need not
be aware of them. For larger pieces, such as piano music, they must be
created explicitly to make sure that you get as many staves as you
need, and that they are in the correct order.  For typesetting pieces
with specialized notation, it can be useful to modify existing or
define new contexts.


Full description of all available contexts is in the program
reference, see
@ifhtml
@internalsref{Contexts}.
@end ifhtml
@ifnothtml 
Translation @arrow{} Context.
@end ifnothtml

@c [TODO: describe propagation]


@menu
* Creating contexts::           
* Changing context properties on the fly ::  
* Modifying context plug-ins::  
* Layout tunings within contexts::  
* Changing context default settings::  
* Defining new  contexts::      
* Which properties to change::  
@end menu

@node Creating contexts
@subsection Creating contexts

For scores with only one voice and one staff, correct contexts are
created automatically. For more complex scores, it is necessary to
create them by hand.  There are three commands which do this.

The easiest command is @code{\new}, and it also the quickest to type.
It is prepended to a music expression, for example

@cindex @code{\new}
@cindex new contexts
@cindex Context, creating

@example
  \new @var{type} @var{music expression}
@end example

@noindent
where @var{type} is a context name (like @code{Staff} or
@code{Voice}).  This command creates a new context, and starts
interpreting @var{music expression} with that.

A practical application of @code{\new} is a score with many
staves. Each part that should be on its own staff, is preceded with 
@code{\new Staff}.

@lilypond[verbatim,relative=2,raggedright]
  << \new Staff { c4 c }
     \new Staff { d4 d }
  >>
@end lilypond

@cindex @code{\context}

Like @code{\new}, the @code{\context} command also directs a music
expression to a context object, but gives the context an extra name. The
syntax is

@example
  \context @var{type} = @var{id} @var{music}
@end example

This form will search for an existing context of type @var{type}
called @var{id}. If that context does not exist yet, it is created.
This is useful if the context is referred to later on. For example, when
setting lyrics the melody is in a named context

@example
 \context Voice = "@b{tenor}" @var{music}
@end example

@noindent
so the texts can be properly aligned to its notes,

@example
\new Lyrics \lyricsto "@b{tenor}" @var{lyrics} 
@end example

@noindent

Another possibility is funneling two different music expressions into
one context. In the following example, articulations and notes are
entered separately,

@verbatim
music = \notes { c4 c4 }
arts = \notes  { s4-. s4-> }
@end verbatim

They are combined by sending both to the same @context{Voice} context,

@verbatim
  << \new Staff \context Voice = "A" \music
     \context Voice = "A" \arts
  >>
@end verbatim
@lilypond[raggedright]
music = \notes { c4 c4 }
arts = \notes  { s4-. s4-> }
\score {
  \notes \relative c''  << \new Staff \context Voice = "A" \music
     \context Voice = "A" \arts
  >>
} 
@end lilypond

@cindex @code{\context}
@cindex creating contexts

The third command for creating contexts is
@example
  \context @var{type} @var{music}
@end example


@noindent
This is similar to @code{\context} with @code{= @var{id}}, but matches
any context of type @var{type}, regardless of its given name.

This variant is used with music expressions that can be interpreted at
several levels. For example, the @code{\applyoutput} command (see
@ref{Running a function on all layout objects}). Without an explicit
@code{\context}, it is usually is applied to @context{Voice}

@example
  \applyoutput #@var{function}   % apply to Voice
@end example

To have it interpreted at the @context{Score} or @context{Staff} level use
these forms

@example
  \context Score \applyoutput #@var{function}
  \context Staff \applyoutput #@var{function}
@end example


@node Changing context properties on the fly
@subsection Changing context properties on the fly

@cindex properties
@cindex @code{\set}
@cindex changing properties

Each context can have different @emph{properties}, variables contained
in that context. They can be changed during the interpretation step.
This is achieved by inserting the @code{\set} command in the music,

@quotation
  @code{\set } @var{context}@code{.}@var{prop}@code{ = #}@var{value} 
@end quotation

For example,
@lilypond[verbatim,relative=2]
  R1*2 
  \set Score.skipBars = ##t
  R1*2
@end lilypond

This command skips measures that have no notes. The result is that
multi rests are condensed.  The value assigned is a Scheme object. In
this case, it is @code{#t}, the boolean True value.

If the @var{context} argument is left out, then the current bottom-most
context (typically @context{ChordNames}, @context{Voice}, or
@context{Lyrics}) is used.  In this example,

@lilypond[verbatim,relative=2]
  c8 c c c
  \set autoBeaming = ##f
  c8 c c c
@end lilypond

@noindent
the @var{context} argument to @code{\set} is left out, and the current
@internalsref{Voice} is used.

Contexts are hierarchical, so if a bigger context was specified, for
example @context{Staff}, then the change would also apply to all
@context{Voice}s in the current stave. The change is applied
`on-the-fly', during the music, so that the setting only affects the
second group of eighth notes.

@cindex @code{\unset} 

There is also an @code{\unset} command,
@quotation
  @code{\set }@var{context}@code{.}@var{prop}
@end quotation

@noindent
which removes the definition of @var{prop}. This command removes
the definition only if it is set in @var{context}. In

@example
  \set Staff.autoBeaming = ##f
  \unset Voice.autoBeaming
@end example

@noindent
the current @context{Voice} does not have the property, and the
definition at @context{Staff} level remains intact. Like @code{\set},
the @var{context} argument does not have to be specified for a bottom
context.

Settings that should only apply to a single time-step can be entered
easily with @code{\once}, for example in

@lilypond[verbatim,relative=2]
  c4
  \once \set fontSize = #4.7
  c4
  c4
@end lilypond

the property @code{fontSize} is unset automatically after the second
note.

A full description of all available context properties is in the
program reference, see
@ifhtml
@internalsref{Tunable-context-properties}.
@end ifhtml
@ifnothtml
Translation @arrow{} Tunable context properties.
@end ifnothtml


@node Modifying context plug-ins
@subsection Modifying context plug-ins

Notation contexts (like Score and Staff) not only store properties,
they also contain plug-ins, called ``engravers'' that create notation
elements. For example, the Voice context contains a
@code{Note_head_engraver} and the Staff context contains a
@code{Key_signature_engraver}.

For a full a description of each plug-in, see 
@ifhtml
@internalsref{Engravers}.
@end ifhtml
@ifnothtml
Program reference @arrow Translation @arrow{} Engravers.
@end ifnothtml
Every context described in
@ifhtml
@internalsref{Contexts}
@end ifhtml
@ifnothtml 
Program reference @arrow Translation @arrow{} Context.
@end ifnothtml
lists the engravers used for that context.


It can be useful to shuffle around these plug-ins. This is done by
starting a new context, with @code{\new} or @code{\context}, and
modifying it like this, 

@example
 \new @var{context} \with @{
   \consists @dots{}
   \consists @dots{}
   \remove  @dots{}
   \remove @dots{}
   @emph{etc.}
 @}
 @var{..music..}
@end example

where the @dots{} should be the name of an engraver. Here is a simple
example which removes @code{Time_signature_engraver} and
@code{Clef_engraver} from a @code{Staff} context,

@lilypond[relative=1, verbatim]
<< \new Staff {
    f2 g
  }
  \new Staff \with {
     \remove "Time_signature_engraver"
     \remove "Clef_engraver"
  } {
    f2 g2
  }
>>
@end lilypond

In the second stave there are no time signature or clef symbols.  This
is a rather crude method of making objects disappear since it will affect
the entire staff. The spacing will be adversely influenced too. A more
sophisticated methods of blanking objects is shown in @ref{Common
tweaks}.

The next example shows a practical application.  Bar lines and time
signatures are normally synchronized across the score.  This is done
by the @code{Timing_engraver}. This plug-in keeps an administration of
time signature, location within the measure, etc. By moving the
@code{Timing_engraver} engraver from Score to Staff context, we can
have a score where each staff has its own time signature.

@cindex polymetric scores


@lilypond[relative=1,raggedright,verbatim]
\new Score \with {
  \remove "Timing_engraver"
} <<
  \new Staff \with {
    \consists "Timing_engraver"
  } {
      \time 3/4
      c4 c c c c c
  }
  \new Staff \with {
    \consists "Timing_engraver"
  } {
       \time 2/4
       c4 c c c c c
  }
>>
@end lilypond


@node Layout tunings within contexts
@subsection Layout tunings within contexts

Each context is responsible for creating certain types of graphical
objects. The settings used for printing these objects are also stored by
context. By changing these settings, the appearance of objects can be
altered.
 
The syntax for this is

@example
  \override @var{context}.@var{name}@code{ #'}@var{property} = #@var{value}
@end example

Here @var{name} is the name of a graphical object, like @code{Stem} or
@code{NoteHead}, and @var{property} is an internal variable of the
formatting system (`grob property' or `layout property'). The latter is a
symbol, so it must be quoted. The subsection @ref{Constructing a
tweak} explains what to fill in for @var{name}, @var{property}, and
@var{value}. Here we only discuss functionality of this command.

The command

@verbatim
  \override Staff.Stem #'thickness = #4.0 
@end verbatim

@noindent
makes stems thicker (the default is 1.3, with staff line thickness as a
unit). Since the command specifies @context{Staff} as context, it only
applies to the current staff. Other staves will keep their normal
appearance.  Here we see the command in action:

@lilypond[verbatim,relative=2]
  c4
  \override Staff.Stem #'thickness = #4.0 
  c4
  c4
  c4
@end lilypond

The @code{\override} command is executed during the interpreting phase,
and changes the definition of the @code{Stem} within
@context{Staff}. After the command all stems are thickened.

Analogous to @code{\set}, the @var{context} argument may be left out,
causing it to default to @context{Voice}, and adding @code{\once} applies
the change during one timestep only 

@lilypond[verbatim,relative=2]
  c4
  \once \override Stem #'thickness = #4.0 
  c4
  c4 
@end lilypond

The @code{\override} must be done before the object is
started. Therefore, when altering @emph{Spanner} objects, like slurs or
beams, the @code{\override} command must be executed at the moment when
the object is created. In this example,


@lilypond[verbatim,relative=2]
  \override Slur #'thickness = #3.0
  c8[( c
  \override Beam #'thickness = #0.6
  c8 c]) 
@end lilypond

@noindent
the slur is fatter and the beam is not. This is because the command for
@code{Beam} comes after the Beam is started. Therefore it has no effect.

Analogous to @code{\unset}, the @code{\revert} command for a context
undoes a @code{\override} command; like with @code{\unset}, it only
affects settings that were made in the same context. In other words, the
@code{\revert} in the next example does not do anything.

@verbatim
  \override Voice.Stem #'thickness = #4.0
  \revert Staff.Stem #'thickness
@end verbatim




@seealso

Internals: @internalsref{OverrideProperty}, @internalsref{RevertProperty},
@internalsref{PropertySet}, @internalsref{All-backend-properties}, and
@internalsref{All-layout-objects}.


@refbugs

The back-end is not very strict in type-checking object properties.
Cyclic references in Scheme values for properties can cause hangs
or crashes, or both.


@node Changing context default settings
@subsection Changing context default settings

The adjustments of the previous chapters can also be entered separate
from the music, in the @code{\paper} block,

@example
  \paper @{
     @dots{}
     \context @{
        \Staff

        \set fontSize = #-2
        \override Stem #'thickness
        \remove "Time_signature_engraver"
      @}
   @}
@end example

Here
@example
  \Staff
@end example

@noindent
takes the existing definition @context{Staff} from the identifier
@code{Staff}. This works analogously to other contexts.

The statements
@example
        \set fontSize = #-2
        \override Stem #'thickness
        \remove "Time_signature_engraver"
@end example

@noindent
affect all staves in the score.

The @code{\set} keyword is optional within the @code{\paper} block, so

@example
  fontSize = #-2
@end example

@noindent
will also work.



@refbugs

It is not possible to collect changes in a variable, and apply them to
one @code{\context} definition by referring to that variable.


@node Defining new  contexts
@subsection Defining new  contexts

Specific contexts, like @context{Staff} and @code{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
@context{Voice} context from scratch.  It will be similar to
@code{Voice}, but print centered slash noteheads only. It can be used
to indicate improvisation in Jazz pieces,

@lilypond[raggedright]
  \paper { \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
  }
  \context { \Staff
    \accepts "ImproVoice"
  }}
  \score { \notes \relative c'' {
    a4 d8 bes8 \new ImproVoice { c4^"ad lib" c 
     c4 c^"undress" c_"while playing :)" c } 
    a1 
  }}
@end lilypond


These settings are again done within a @code{\context} block inside a
@code{\paper} block,

@example
  \paper @{
    \context @{
      @dots{}
    @}
  @}
@end example

In the following discussion, the example input shown should go on the
@dots{} in the previous fragment.

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

@verbatim
  \name ImproVoice
@end verbatim

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

@verbatim
  \alias Voice
@end verbatim

The context will print notes, and instructive texts

@verbatim
  \consists Note_heads_engraver
  \consists Text_engraver
@end verbatim

but only on the center line,

@verbatim
  \consists Pitch_squash_engraver
  squashedPosition = #0
@end verbatim

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

The notes look like a  slash, without a stem,

@verbatim
    \override NoteHead #'style = #'slash
    \override Stem #'transparent = ##t
@end verbatim


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

@example
 \type "Engraver_group_engraver"
@end example

Putting together, we get

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

Contexts form hierarchies. We want to hang the @context{ImproVoice}
under @context{Staff}, just like normal @code{Voice}s. Therefore, we
modify the @code{Staff} definition with the @code{\accepts}
command,@footnote{The opposite of @code{\accepts} is @code{\denies},
which is sometimes when reusing existing context definitions. }



@verbatim
  \context {
    \Staff
    \accepts ImproVoice    
  }
@end verbatim 

Putting both into a @code{\paper} block, like

@example
  \paper @{
    \context @{
      \name ImproVoice
      @dots{}
    @}
  \context @{
    \Staff
    \accepts "ImproVoice"
  @}
@}
@end example

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

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

    
@node Which properties to change
@subsection Which properties to change


There are many different properties.  Not all of them are listed in
this manual. However, the program reference lists them all in the
section @internalsref{Tunable-context-properties}, and most properties
are demonstrated in one of the
@ifhtml
@uref{../../../../input/test/out-www/collated-files.html,tips-and-tricks}
@end ifhtml
@ifnothtml
tips-and-tricks
@end ifnothtml
examples.


@node Tuning output
@section Tuning output

In the previous section, we have already touched on a command that
changes layout details, the @code{\override} command. In this section,
we will look at in more detail how to use the command in practice.
First, we will give a a few versatile commands, which are sufficient
for many situations. The next section will discuss general use of
@code{\override}.

@ignore
There are situations where default layout decisions are not
sufficient.  In this section we discuss ways to override these
defaults.

Formatting is internally done by manipulating so called objects
(graphic objects). Each object carries with it a set of properties
(object or layout properties) specific to the object.  For example, a
stem object has properties that specify its direction, length, and
thickness.

The most direct way of tuning the output is to alter the values of
these properties. There are two ways of doing that: First, you can
temporarily change the definition of one type of object, thus
affecting a whole set of objects.  Second, you can select one specific
object, and set a layout property in that object.

Do not confuse layout properties with translation
properties. Translation properties always use a mixed caps style
naming, and are manipulated using @code{\set} and @code{\unset}: 
@example
  \set Context.propertyName = @var{value}
@end example

Layout properties are use Scheme style variable naming, i.e.  lower
case words separated with dashes. They are symbols, and should always
be quoted using @code{#'}.  For example, this could be an imaginary
layout property name:
@example
  #'layout-property-name
@end example

@end ignore

@menu
* Common tweaks::               
* Constructing a tweak::        
* Navigating the program reference::  
* Layout interfaces::           
* Determining the grob property::  
@end menu



@node Common tweaks
@subsection Common tweaks

Some overrides are so common that predefined commands are provided as
a short-cut, for example, @code{\slurUp} and @code{\stemDown}. These
commands are described in
@ifhtml
the
@end ifhtml
@ref{Notation manual}, under the sections for slurs and stems
respectively.

The exact tuning possibilities for each type of layout object are
documented in the program reference of the respective
object. However, many layout objects share properties, which can be
used to apply generic tweaks.  We mention a few of these:

@itemize @bullet
@item The @code{extra-offset} property, which
@cindex @code{extra-offset}
has a pair of numbers as value, moves around objects in the printout.
The first number controls left-right movement; a positive number will
move the object to the right.  The second number controls up-down
movement; a positive number will move it higher.  The units of these
offsets are staff-spaces.  The @code{extra-offset} property is a
low-level feature: the formatting engine is completely oblivious to
these offsets.

In the following example, the second fingering is moved a little to
the left, and 1.8 staff space downwards:

@cindex setting object properties

@lilypond[relative=1,verbatim]
\stemUp
f-5
\once \override Fingering
    #'extra-offset = #'(-0.3 . -1.8) 
f-5
@end lilypond

@item
Setting the @code{transparent} property will cause an object to be printed
in `invisible ink': the object is not printed, but all its other
behavior is retained. The object still takes up space, it takes part in
collisions, and slurs, and ties and beams can be attached to it.

@cindex transparent objects
@cindex removing objects
@cindex hiding objects
@cindex invisible objects
The following example demonstrates how to connect different voices
using ties. Normally, ties only connect two notes in the same
voice. By introducing a tie in a different voice,

@lilypond[fragment,relative=2]
  << {
      b8~ b8\noBeam
  } \\ {
       b[ g8]
  } >>
@end lilypond

@noindent
and blanking a stem in that voice, the tie appears to cross voices:

@lilypond[fragment,relative=2,verbatim]
  << {
      \once \override Stem #'transparent = ##t
      b8~ b8\noBeam
  } \\ {
       b[ g8]
  } >>
@end lilypond

@item
The @code{padding} property for objects with
@cindex @code{padding}
@code{side-position-interface} can be set to increase distance between
symbols that are printed above or below notes. We only give an
example; a more elaborate explanation is in @ref{Constructing a
tweak}:

@lilypond[relative=1,verbatim]
  c2\fermata
  \override Script #'padding = #3
  b2\fermata
@end lilypond

@end itemize

More specific overrides are also possible.  The next section
discusses in depth how to figure out these statements for yourself.


@node Constructing a tweak
@subsection Constructing a tweak

The general procedure of changing output, that is, entering
a command like

@example
        \override Voice.Stem #'thickness = #3.0
@end example

@noindent
means that we have to determine these bits of information:

@itemize
@item the context: here @context{Voice}.
@item the layout object: here @code{Stem}.
@item the layout property: here @code{thickness}
@item a sensible value: here @code{3.0}
@end itemize  


@cindex internal documentation
@cindex finding graphical objects
@cindex graphical object descriptions 
@cindex tweaking
@cindex @code{\override}
@cindex @code{\set}
@cindex internal documentation

We demonstrate how to glean this information from the notation manual
and the program reference.

The program reference is a set of HTML pages, which is part of the
documentation package. On Unix systems, it is typically in
@file{/usr/share/doc/lilypond}. If you have them, it is best to
bookmark them in your webbrowser, because you will need them.  They
are also available on the web: go to the
@uref{http://lilypond.org,LilyPond website}, click ``Documentation'',
select the correct version, and then click ``Program reference.''

If you have them, use the local HTML files.  They will load faster,
and they are exactly matched to LilyPond version installed.
 

@node Navigating the program reference
@subsection Navigating the program reference

Suppose we want to move the fingering indication in the fragment
below:

@lilypond[relative=2,verbatim]
c-2
\stemUp
f
@end lilypond

If you visit the documentation of @code{Fingering} (in @ref{Fingering
instructions}), you will notice that there is written:

@quotation
@seealso

Program reference: @internalsref{FingerEvent} and @internalsref{Fingering}.

@end quotation

This  fragments points to two parts of the program reference: a page
on @code{FingerEvent} and on @code{Fingering}.

The page on  @code{FingerEvent} describes the properties of the  music
expression for the input @code{-2}. The page contains many links
forward.  For example, it says

@quotation
  Accepted by: @internalsref{Fingering_engraver},
@end quotation 

@noindent
That link brings us to the documentation for the Engraver, the
plug-in, which says

@quotation
  This engraver creates the following layout objects: @internalsref{Fingering}.
@end quotation

In other words, once the @code{FingerEvent}s are interpreted, the
@code{Fingering_engraver} plug-in will process them.
The @code{Fingering_engraver} is also listed to create
@internalsref{Fingering} objects,


  Lo and behold, that is also the
second bit of information listed under @b{See also} in the Notation
manual. By clicking around in the program reference, we can follow the
flow of information within the program, either forward (like we did
here), or backwards, following links like this:

@itemize @bullet

@item @internalsref{Fingering}:
  @internalsref{Fingering} objects are created by:
  @b{@internalsref{Fingering_engraver}}

@item @internalsref{Fingering_engraver}:
Music types accepted: @b{@internalsref{fingering-event}}
@item @internalsref{fingering-event}:
Music event type @code{fingering-event} is in Music objects of type
@b{@internalsref{FingerEvent}}
@end itemize

This path goes against the flow of information in the program: it
starts from the output, and ends at the input event.

The program reference can also be browsed like a normal document.  It
contains a chapter on
@ifhtml
@internalsref{Music-definitions},
@end ifhtml
@ifnothtml
Music definitions
@end ifnothtml
on @internalsref{Translation}, and the @internalsref{Backend}. Every
chapter lists all the definitions used, and all properties that may be
tuned.

 
@node Layout interfaces
@subsection Layout interfaces

@internalsref{Fingering} is a layout object. Such an object is a
symbol within the score. It has properties, which store numbers (like
thicknesses and directions), but also pointers to related objects.
A layout object is also called @emph{grob},
@cindex grob
which is short for Graphical Object.


The page for @code{Fingering} lists the definitions for the
@code{Fingering} object. For example, the page says

@quotation
  @code{padding} (dimension, in staff space):
  
  @code{0.6}
@end quotation

which means that the number will be kept at a distance of at least 0.6
of the note head.


Each layout object may have several functions as a notational or
typographical element. For example, the Fingering object
has the following aspects

@itemize @bullet
@item Its size is independent of the horizontal spacing, unlike slurs or beams

@item It is a piece of text. Granted, it's usually  a very short text.

@item That piece of text is typeset with a font, unlike slurs or beams.
@item Horizontally, the center of the symbol should be aligned to the
center of the notehead
@item Vertically, the symbol is placed next to the note and the staff.

@item The
 vertical position is also coordinated with other super and subscript
symbols
@end itemize

Each of these aspects is captured in a so-called @emph{interface},
which are listed on the @internalsref{Fingering} page at the bottom

@quotation
This object supports the following interfaces:
@internalsref{item-interface},
@internalsref{self-alignment-interface},
@internalsref{side-position-interface}, @internalsref{text-interface},
@internalsref{text-script-interface}, @internalsref{font-interface},
@internalsref{finger-interface}, and @internalsref{grob-interface}.
@end quotation

Clicking any of the links will take you to the page of the respective
object interface.  Each interface has a number of properties.  Some of
them are not user-serviceable (``Internal properties''), but others
are.

We have been talking of `the' @code{Fingering} object, but actually it
does  not amount to much. The initialization file
@file{scm/define-grobs.scm} shows the soul of the `object',

@verbatim
   (Fingering
     . (
        (print-function . ,Text_item::print)
        (padding . 0.6)
        (staff-padding . 0.6)
        (self-alignment-X . 0)
        (self-alignment-Y . 0)
        (script-priority . 100)
        (font-encoding . number)
        (font-size . -5)
        (meta . ((interfaces . (finger-interface font-interface
               text-script-interface text-interface
               side-position-interface self-alignment-interface
               item-interface))))
  ))
@end verbatim

as you can see, @code{Fingering} is nothing more than a bunch of
variable settings, and the webpage is directly generated from this
definition.

@node Determining the grob property
@subsection Determining the grob property


Recall that we wanted to change the position of the @b{2} in 

@lilypond[relative=2,verbatim]
c-2
\stemUp
f
@end lilypond

Since the @b{2} is vertically positioned next to its note, we have to
meddle with the interface associated with this positioning. This is
done using @code{side-position-interface}. The page for this interface 
says

@quotation
@code{side-position-interface}

  Position a victim object (this one) next to other objects (the
  support).  The property @code{direction} signifies where to put the
  victim object relative to the support (left or right, up or down?)
@end quotation

@cindex padding
@noindent
below this description, the variable @code{padding} is described as
@quotation
@table @code
@item padding
 (dimension, in staff space)

 add this much extra space between objects that are next to each
  other. 
@end table
@end quotation

By increasing the value of @code{padding}, we can move away the
fingering.  The following command inserts 3 staff spaces of white
between the note and the fingering:
@example
\once \override Fingering #'padding = #3
@end example

Inserting this command before the Fingering object is created,
i.e. before @code{c2}, yields the following result:

@lilypond[relative=2,fragment,verbatim]
\once \override Fingering
    #'padding = #3
c-2
\stemUp
f
@end lilypond


In this case, the context for this tweak is @context{Voice}, which
does not have to be specified for @code{\override}.  This fact can
also be deduced from the program reference, for the page for the
@internalsref{Fingering_engraver} plug-in says

@quotation
  Fingering_engraver is part of contexts: @dots{} @b{@internalsref{Voice}}
@end quotation


@node Fonts
@section Fonts

@menu
* Selecting font sizes::        
* Font selection::              
@end menu



@node Selecting font sizes
@subsection Selecting font sizes

The most common thing to change about the appearance of fonts is their
size. The font size of any context can be easily changed by setting
the @code{fontSize} property for that context.  Its value is a number:
negative numbers make the font smaller, positive numbers larger. An
example is given below:
@c
@lilypond[fragment,relative=1,verbatim]
  c4 c4 \set fontSize = #-3
  f4 g4
@end lilypond
This command will set @code{font-size} (see below) in all layout
objects in the current context. It does not change the size of
variable symbols, such as beams or slurs.

The font size is set by modifying the @code{font-size} property.  Its
value is a number indicating the size relative to the standard size.
Each step up is an increase of approximately 12% of the font size. Six
steps is exactly a factor two. The Scheme function @code{magstep}
converts a @code{font-size} number to a scaling factor.

LilyPond has fonts in different design sizes: the music fonts for
smaller sizes are chubbier, while the text fonts are relatively wider.
Font size changes are achieved by scaling the design size that is
closest to the desired size.

The @code{font-size} mechanism does not work for fonts selected
through @code{font-name}. These may be scaled with
@code{font-magnification}.


One of the uses of @code{fontSize} is to get smaller symbols for cue
notes. An elaborate example of those is in
@inputfileref{input/test,cue-notes.ly}.

@cindex @code{font-style}

@refcommands

The following commands set @code{fontSize} for the current voice:

@cindex @code{\tiny}
@code{\tiny}, 
@cindex @code{\small}
@code{\small}, 
@cindex @code{\normalsize}
@code{\normalsize}.



@cindex magnification
@cindex cue notes


@node Font selection
@subsection Font selection

Font selection for the standard fonts, @TeX{}'s Computer Modern fonts,
can also be adjusted with a more fine-grained mechanism.  By setting
the object properties described below, you can select a different font;
all three mechanisms work for every object that supports
@code{font-interface}:


@itemize @bullet
@item @code{font-encoding}
is a symbol that sets layout of the glyphs. Choices include
@code{text} for normal text, @code{braces} (for piano staff braces),
@code{music} (the standard music font, including ancient glyphs),
@code{dynamic} (for dynamic signs) and @code{number} for the number
font.


@item @code{font-family}
 is a symbol indicating the general class of the typeface.  Supported are
@code{roman} (Computer Modern), @code{sans}, and @code{typewriter}.
  
@item @code{font-shape}
  is a symbol indicating the shape of the font, there are typically
several font shapes available for each font family. Choices are
@code{italic}, @code{caps}, and @code{upright}.

@item @code{font-series}
is a  symbol indicating the series of the font. There are typically several
font series for each font family and shape. Choices are @code{medium}
and @code{bold}. 

@end itemize

Fonts selected in the way sketched above come from a predefined style
sheet.

 The font used for printing a object can be selected by setting
@code{font-name}, e.g.
@example
  \override Staff.TimeSignature
      #'font-name = #"cmr17"
@end example

@noindent
Any font can be used, as long as it is available to @TeX{}. Possible
fonts include foreign fonts or fonts that do not belong to the
Computer Modern font family.  The size of fonts selected in this way
can be changed with the @code{font-magnification} property.  For
example, @code{2.0} blows up all letters by a factor 2 in both
directions.

@cindex font size
@cindex font magnification



@seealso

Init files: @file{ly/declarations-init.ly} contains hints how new
fonts may be added to LilyPond.

@refbugs

No style sheet is provided for other fonts besides the @TeX{}
Computer Modern family.

@cindex font selection
@cindex font magnification
@cindex @code{font-interface}


@node Text markup
@section Text markup
@cindex text markup
@cindex markup text


@cindex typeset text

LilyPond has an internal mechanism to typeset texts. You can access it
with the keyword @code{\markup}. Within markup mode, you can enter texts
similar to lyrics: simply enter them, surrounded by spaces:
@cindex markup

@lilypond[verbatim,fragment,relative=1]
 c1^\markup { hello }
 c1_\markup { hi there }
 c1^\markup { hi \bold there, is \italic anyone home? }
@end lilypond

@cindex font switching

The markup in the example demonstrates font switching commands.  The
command @code{\bold} and @code{\italic} apply to the first following 
word only; enclose a set of texts with braces to apply a command
to more words:
@example
  \markup @{ \bold @{ hi there @} @}
@end example

@noindent
For clarity, you can also do this for single arguments, e.g.

@verbatim
  \markup { is \italic { anyone } home }
@end verbatim

@cindex font size, texts


In markup mode you can compose expressions, similar to mathematical
expressions, XML documents, and music expressions.  The braces group
notes into horizontal lines. Other types of lists also exist: you can
stack expressions grouped with @code{<} and @code{>} vertically with
the command @code{\column}. Similarly, @code{\center-align} aligns
texts by their center lines:

@lilypond[verbatim,fragment,relative=1]
 c1^\markup { \column < a bbbb c > }
 c1^\markup { \center-align < a bbbb c > }
 c1^\markup { \line < a b c > }
@end lilypond


Markups can be stored in variables, and these variables
may be attached to notes, like
@verbatim
allegro = \markup { \bold \large { Allegro } }
\notes { a^\allegro b c d }
@end verbatim


Some objects have alignment procedures of their own, which cancel out
any effects of alignments applied to their markup arguments as a
whole.  For example, the @internalsref{RehearsalMark} is horizontally
centered, so using @code{\mark \markup @{ \left-align .. @}} has no
effect.

Similarly, for moving whole texts over notes with
@code{\raise}, use the following trick:
@example
  "" \raise #0.5 raised
@end example

The text @code{raised} is now raised relative to the empty string
@code{""} which is not visible.  Alternatively, complete objects can
be moved with layout properties such as @code{padding} and
@code{extra-offset}.



@seealso

Init files:  @file{scm/new-markup.scm}.


@refbugs

Text layout is ultimately done by @TeX{}, which does kerning of
letters.  LilyPond does not account for kerning, so texts will be
spaced slightly too wide.

Syntax errors for markup mode are confusing.

Markup texts cannot be used in the titling of the @code{\header}
field. Titles are made by La@TeX{}, so La@TeX{} commands should be used
for formatting.



@menu
* Overview of text markup commands::  
@end menu

@node  Overview of text markup commands
@subsection Overview of text markup commands

@include markup-commands.tely


@node Global layout
@section Global layout

The global layout determined by three factors: the page layout, the
line breaks, and the spacing. These all influence each other. The
choice of spacing determines how densely each system of music is set,
which influences where line breaks are chosen, and thus
ultimately how many pages a piece of music takes. This section
explains how to tune the algorithm for spacing.

Globally spoken, this procedure happens in three steps: first,
flexible distances (``springs'') are chosen, based on durations. All
possible line breaking combination are tried, and the one with the
best results --- a layout that has uniform density and requires as
little stretching or cramping as possible --- is chosen. When the score
is processed by @TeX{}, each page is filled with systems, and page breaks
are chosen whenever the page gets full.



@menu
* Setting global staff size::   
* Vertical spacing::            
* Horizontal spacing::          
* Line breaking::               
* Page layout::                 
@end menu


@node Setting global staff size
@subsection Setting global staff size

@cindex font size, setting
@cindex staff size, setting
@cindex @code{paper} file

The Feta font provides musical symbols at eight  different
sizes. Each font is tuned for a different staff size: at a smaller size
the font becomes heavier, to match the relatively heavier staff lines.
The recommended font sizes are listed in the following table:

@multitable @columnfractions  .25 .25 .25 .25

@item @b{font name}
@tab @b{staff height (pt)}
@tab @b{staff height (mm)}
@tab @b{use}

@item feta11
@tab 11.22
@tab 3.9 
@tab pocket scores

@item feta13
@tab 12.60
@tab 4.4
@tab

@item feta14
@tab 14.14
@tab 5.0
@tab 

@item feta16
@tab 15.87
@tab 5.6
@tab 

@item feta18
@tab 17.82
@tab 6.3
@tab song books

@item feta20
@tab 17.82
@tab 7.0
@tab standard parts 

@item feta23
@tab 22.45 
@tab 7.9
@tab 

@item feta26
@tab 25.2 
@tab 8.9
@tab
@c modern rental material  ?

@end multitable

These fonts are available in any sizes. The context property
@code{fontSize} and the layout property @code{staff-space} (in
@internalsref{StaffSymbol}) can be used to tune size for individual
staves. The size of individual staves are relative to the global size,
which can be set   in the following manner:

@example
  #(set-global-staff-size 14)
@end example

This sets the global default size to 14pt staff height, and scales all
fonts accordingly.

@seealso

This manual: @ref{Selecting font sizes}.



@menu
* Vertical spacing::            
* Horizontal spacing::          
* Line breaking::               
* Page layout::                 
@end menu

@node Vertical spacing
@subsection Vertical spacing

@cindex vertical spacing
@cindex distance between staves
@cindex staff distance
@cindex between staves, distance
@cindex staves per page
@cindex space between staves

The height of each system is determined automatically by LilyPond, to
keep systems from bumping into each other, some minimum distances are
set.  By changing these, you can put staves closer together, and thus
put more  systems onto one page.

Normally staves are stacked vertically. To make
staves maintain a distance, their vertical size is padded. This is
done with the property @code{minimumVerticalExtent}. It takes a pair
of numbers, so if you want to make it smaller from its, then you could
set
@example
  \set Staff.minimumVerticalExtent = #'(-4 . 4)
@end example
This sets the vertical size of the current staff to 4 staff spaces on
either side of the center staff line.  The argument of
@code{minimumVerticalExtent} is interpreted as an interval, where the
center line is the 0, so the first number is generally negative.  The
staff can be made larger at the bottom by setting it to @code{(-6
. 4)}.

The piano staves are handled a little differently: to make cross-staff
beaming work correctly, it is necessary that the distance between staves
is fixed beforehand.  This is also done with a
@internalsref{VerticalAlignment} object, created in
@internalsref{PianoStaff}. In this object the distance between the
staves is fixed by setting @code{forced-distance}. If you want to
override this, use a @code{\context} block as follows:
@example
  \paper @{
    \context @{
      \PianoStaff
      \override VerticalAlignment #'forced-distance = #9
    @}
    @dots{}
  @}
@end example
This would bring the staves together at a distance of 9 staff spaces,
measured from the center line of each staff.

@seealso

Internals: Vertical alignment of staves is handled by the
@internalsref{VerticalAlignment} object.




@node Horizontal spacing
@subsection Horizontal Spacing

The spacing engine translates differences in durations into
stretchable distances (``springs'') of differing lengths. Longer
durations get more space, shorter durations get less.  The shortest
durations get a fixed amount of space (which is controlled by
@code{shortest-duration-space} in the @internalsref{SpacingSpanner} object). 
The longer the duration, the more space it gets: doubling a
duration adds a fixed amount (this amount is controlled by
@code{spacing-increment}) of space to the note.

For example, the following piece contains lots of half, quarter, and
8th notes, the eighth note is followed by 1 note head width (NHW). 
The quarter note is followed by 2 NHW, the half by 3 NHW, etc.
@lilypond[fragment,verbatim,relative=1] c2 c4. c8 c4. c8 c4. c8 c8
c8 c4 c4 c4
@end lilypond

Normally, @code{shortest-duration-space} is set to 1.2, which is the
width of a note head, and @code{shortest-duration-space} is set to
2.0, meaning that the shortest note gets 2 NHW (i.e. 2 times
@code{shortest-duration-space}) of space. For normal notes, this space
is always counted from the left edge of the symbol, so the shortest
notes are generally followed by one NHW of space.

If one would follow the above procedure exactly, then adding a single
32th note to a score that uses 8th and 16th notes, would widen up the
entire score a lot. The shortest note is no longer a 16th, but a 32nd,
thus adding 1 NHW to every note. To prevent this, the
shortest duration for spacing is not the shortest note in the score,
but the most commonly found shortest note.  Notes that are even
shorter this are followed by a space that is proportional to their
duration relative to the common shortest note.  So if we were to add
only a few 16th notes to the example above, they would be followed by
half a NHW:

@lilypond[fragment,verbatim,relative=2]
 c2 c4. c8 c4. c16[ c] c4. c8 c8 c8 c4 c4 c4
@end lilypond

The most common shortest duration is determined as follows: in every
measure, the shortest duration is determined. The most common short
duration, is taken as the basis for the spacing, with the stipulation
that this shortest duration should always be equal to or shorter than
1/8th note. The shortest duration is printed when you run lilypond
with @code{--verbose}.  These durations may also be customized. If you
set the @code{common-shortest-duration} in
@internalsref{SpacingSpanner}, then this sets the base duration for
spacing. The maximum duration for this base (normally 1/8th), is set
through @code{base-shortest-duration}.

@cindex @code{common-shortest-duration}
@cindex @code{base-shortest-duration}
@cindex @code{stem-spacing-correction}
@cindex @code{spacing}

In the Introduction it was explained that stem directions influence
spacing. This is controlled with @code{stem-spacing-correction}
property in @internalsref{NoteSpacing}, which are generated for every
@internalsref{Voice} context. The @code{StaffSpacing} object
(generated at @internalsref{Staff} context) contains the same property
for controlling the stem/bar line spacing. The following example
shows these corrections, once with default settings, and once with
exaggerated corrections:

@lilypond
    \score { \notes {
      c'4 e''4 e'4 b'4 |
      b'4 e''4 b'4 e''4|
      \override Staff.NoteSpacing #'stem-spacing-correction = #1.5
      \override Staff.StaffSpacing #'stem-spacing-correction = #1.5
      c'4 e''4 e'4 b'4 |
      b'4 e''4 b'4 e''4|      
    }
    \paper { raggedright = ##t } }
@end lilypond

@cindex SpacingSpanner, overriding properties

Properties of the  @internalsref{SpacingSpanner} must be overridden
from the @code{\paper} block, since the @internalsref{SpacingSpanner} is
created before any property commands are interpreted.
@example
\paper @{ \context  @{
  \Score
  \override SpacingSpanner #'spacing-increment = #3.0
@} @}
@end example


@seealso

Internals: @internalsref{SpacingSpanner}, @internalsref{NoteSpacing},
@internalsref{StaffSpacing}, @internalsref{SeparationItem}, and
@internalsref{SeparatingGroupSpanner}.

@refbugs

Spacing is determined on a score wide basis. If you have a score that
changes its character (measured in durations) halfway during the
score, the part containing the longer durations will be spaced too
widely.

There is no convenient mechanism to manually override spacing.  The
following work-around may be used to insert extra space into a score.
@example
 \once \override Score.SeparationItem #'padding = #1
@end example

No work-around exists for decreasing the amount of space.


@menu
* Line breaking::               
* Page layout::                 
@end menu

@node Line breaking
@subsection Line breaking

@cindex line breaks
@cindex breaking lines

Line breaks are normally computed automatically. They are chosen such
that lines look neither cramped nor loose, and that consecutive lines
have similar density.

Occasionally you might want to override the automatic breaks; you can
do this by  specifying @code{\break}. This will force a line break at
this point.  Line breaks can only occur at places where there are bar
lines.  If you want to have a line break where there is no bar line,
you can force an invisible bar line by entering @code{\bar
""}. Similarly, @code{\noBreak} forbids a line break at a 
point.


@cindex regular line breaks
@cindex four bar music. 

For line breaks at regular intervals  use @code{\break} separated by
skips and repeated with @code{\repeat}:
@example
<<  \repeat unfold 7 @{
         s1 \noBreak s1 \noBreak
         s1 \noBreak s1 \break  @}
   @emph{the real music}
>> 
@end  example

@noindent
This makes the following 28 measures (assuming 4/4 time) be broken every
4 measures, and only there.

@refcommands

@code{\break}, and @code{\noBreak}.
@cindex @code{\break}
@cindex @code{\noBreak}

@seealso

Internals: @internalsref{BreakEvent}.


@node Page layout
@subsection Page layout

@cindex page breaks
@cindex breaking pages

@cindex @code{indent}
@cindex @code{linewidth}

The most basic settings influencing the spacing are @code{indent} and
@code{linewidth}. They are set in the @code{\paper} block. They
control the indentation of the first line of music, and the lengths of
the lines.

If  @code{raggedright} is set to true in the @code{\paper}
block, then the lines are justified at their natural length. This
useful for short fragments, and for checking how tight the natural
spacing is.

@cindex page layout
@cindex vertical spacing

The option @code{raggedlast} is similar to @code{raggedright}, but
only affects the last line of the piece. No restrictions are put on
that line. The result is similar to formatting paragraphs. In a
paragraph, the last line simply takes its natural length.

The page layout process happens outside the LilyPond formatting
engine: variables controlling page layout are passed to the output,
and are further interpreted by @code{lilypond} wrapper program. It
responds to the following variables in the @code{\paper} block.  The
spacing between systems is controlled with @code{interscoreline}, its
default is 16pt.  The distance between the score lines will stretch in
order to fill the full page @code{interscorelinefill} is set to a
positive number.  In that case @code{interscoreline} specifies the
minimum spacing.

@cindex @code{textheight}
@cindex @code{interscoreline}
@cindex @code{interscorelinefill}

If the variable @code{lastpagefill} is defined,
@c fixme: this should only be done if lastpagefill= #t 
systems are evenly distributed vertically on the last page.  This
might produce ugly results in case there are not enough systems on the
last page.  The @command{lilypond-book} command ignores
@code{lastpagefill}.  See @ref{lilypond-book manual} for more
information.

@cindex @code{lastpagefill}

Page breaks are normally computed by @TeX{}, so they are not under
direct control of LilyPond.  However, you can insert commands into
the @file{.tex} output to instruct @TeX{} where to break pages.  This
is done by setting the @code{between-systems-strings} on the
@internalsref{NonMusicalPaperColumn} where the system is broken.
An example is shown in @inputfileref{input/regression,between-systems.ly}.
The predefined command @code{\newpage} also does this.

@cindex paper size
@cindex page size
@cindex @code{papersize}

To change the paper size, there are two commands,
@example
        #(set-default-paper-size "a4")
        \paper@{
           #(set-paper-size "a4")
        @}
@end example
The second one sets the size of the @code{\paper} block that it's in.

@refcommands

@cindex @code{\newpage}
@code{\newpage}. 


@seealso

In this manual: @ref{Invoking lilypond}.

Examples: @inputfileref{input/regression,between-systems.ly}.

Internals: @internalsref{NonMusicalPaperColumn}.

@refbugs

LilyPond has no concept of page layout, which makes it difficult to
reliably choose page breaks in longer pieces.




@node Output details
@section Output details

The default output format is La@TeX{}, which should be run
through La@TeX{}.  Using the option @option{-f}
(or @option{--format}) other output formats can be selected also, but
 none of them work reliably.

Now the music is output system by system (a `system' is a single line
from the score, consisting of staves belonging together).  From
@TeX{}'s point of view, a system is an @code{\hbox} which contains a
lowered @code{\vbox} so that it is centered vertically on the baseline
of the text.  Between systems, @code{\interscoreline} is inserted
vertically to have stretchable space.  The horizontal dimension of the
@code{\hbox} is given by the @code{linewidth} parameter from
LilyPond's @code{\paper} block.

After the last system LilyPond emits a stronger variant of
@code{\interscoreline} only if the macro
@code{\lilypondpaperlastpagefill} is not defined (flushing the systems
to the top of the page).  You can avoid that by setting the variable
@code{lastpagefill} in LilyPond's @code{\paper} block.

@c FIXME: broken by page layout
It is possible to fine-tune the vertical offset further by defining the
macro @code{\lilypondscoreshift}:

@example
\def\lilypondscoreshift@{0.25\baselineskip@}
@end example

@noindent
where @code{\baselineskip} is the distance from one text line to the next.

Here an example how to embed a small LilyPond file @code{foo.ly} into
running La@TeX{} text without using the @code{lilypond-book} script
(@pxref{lilypond-book manual}):

@example
\documentclass@{article@}

\def\lilypondpaperlastpagefill@{@}
\lineskip 5pt
\def\lilypondscoreshift@{0.25\baselineskip@}

\begin@{document@}
This is running text which includes an example music file
\input@{foo.tex@}
right here.
\end@{document@}
@end example

The file @file{foo.tex} has been simply produced with

@example
  lilypond-bin foo.ly
@end example

The call to @code{\lineskip} assures that there is enough vertical space
between the LilyPond box and the surrounding text lines.