* scm/document-backend.scm (interface-doc): sort grob list for interface.

[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 that 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 how to tune them.

Which controls are available for tuning is described in a separate
document, the @internalsref{Program reference} manual. This manual
lists all different variables, functions and options available in
LilyPond. It is available 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 X 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::               
* Font Size::                   
* 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 LilyPondese 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). For entering lists, use a quote @code{'} and 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 things 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 is contextual information. and it can be present 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.  To match this hierarchy, LilyPond's interpretation step is
hierarchical.  There are interpretation contexts, like
@context{Voice}, Staff and Score, and each level can maintain its own
properties.

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

@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

[TODO: propagation]

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

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

@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, gets a @code{\new
Staff}.

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

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 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



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 @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

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.

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 only removes
the definition 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, it will affect the
entire staff. The spacing will be adversely influenced too. More
sophisticated methods of blanking objects are shown in (TODO).

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 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}.  @var{property} is an internal variable of the
formatting system (`grob property' or `layout property'). It is a
symbol, so it must be quoted. The subsection refTODO 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 only one timestep

@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 that
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
and/or crashes.


@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 @{
        \StaffContext

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

This
@example
  \StaffContext
@end example

@noindent
takes the existing definition @context{Staff} from the identifier
@code{StaffContext}. This works analogously other contexts, so the
existing definition  of @code{Voice} is in 
@code{\VoiceContext}.

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 referencing 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 { \StaffContext
    \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{} of 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

Put 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 {
    \StaffContext
    \accepts ImproVoice    
  }
@end verbatim 

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

@example
  \paper @{
    \context @{
      \name ImproVoice
      @dots{}
    @}
  \context @{
    \StaffContext
    \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{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




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 that object.  For example, a
stem object has properties that specify its direction, length and
thickness.

The most direct way of tuning the output is by altering 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


@menu
* Common tweaks::               
* Constructing a tweak::        
@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 couple 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 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, 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 following section
discusses in depth how to figure out these statements for yourself.


@node Constructing a tweak
@subsection Constructing a tweak


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



Three pieces of information are required to use @code{\override} and
@code{\set}: the name of the layout object, the context and the name
of the property.  We demonstrate how to glean this information from
the notation manual and the program reference.

The generated documentation is a set of HTML pages which should be
included if you installed a binary distribution, typically in
@file{/usr/share/doc/lilypond}.  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.'' It is advisable to bookmark the local HTML
files. They will load faster than the ones on the web and matches the
version of LilyPond you are using.
 


@c  [TODO: revise for new site.]

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

Internals: @internalsref{FingerEvent} and @internalsref{Fingering}.

@end quotation

@separate

@noindent
In other words, the fingerings once entered, are internally stored as
@code{FingerEvent} music objects. When printed, a @code{Fingering}
layout object is created for every @code{FingerEvent}.

The Fingering object has a number of different functions, and each of
those is captured in an interface. The interfaces are listed under
@internalsref{Fingering} in the program reference.



The @code{Fingering} object has a fixed size
(@internalsref{item-interface}), the symbol is a piece of text
(@internalsref{text-interface}), whose font can be set
(@internalsref{font-interface}).  It is centered horizontally
(@internalsref{self-alignment-interface}), it is placed vertically
next to other objects (@internalsref{side-position-interface}), and
its placement is coordinated with other scripts
(@internalsref{text-script-interface}).  It also has the standard
@internalsref{grob-interface} (grob stands for Graphical object)
@cindex grob
@cindex graphical object
@cindex layout object
@cindex object, layout 
with all the variables that come with
it.  Finally, it denotes a fingering instruction, so it has
@internalsref{finger-interface}.

For the vertical placement, we have to look under
@code{side-position-interface}:
@quotation
@code{side-position-interface}

  Position a victim object (this one) next to other objects (the
  support).  In this case, 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. Default value: @code{0.6}
@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

The context name @code{Voice} in the example above can be determined
as follows. In the documentation for @internalsref{Fingering}, it says
@quotation
Fingering grobs are created by: @internalsref{Fingering_engraver} @c
@end quotation

Clicking @code{Fingering_engraver} shows the documentation of
the module responsible for interpreting the fingering instructions and
translating them to a @code{Fingering} object.  Such a module is called
an @emph{engraver}.  The documentation of the @code{Fingering_engraver}
says
@example
Fingering_engraver is part of contexts: Voice 
@end example
so tuning the settings for Fingering should be done with
@example
  \override Fingering @dots{}
@end example

Of course, the tweak may also done in a larger context than
@code{Voice}, for example, @internalsref{Staff} or
@internalsref{Score}.

@seealso

Internals: the program reference also contains alphabetical lists of
@internalsref{Contexts}, @internalsref{All-layout-objects} and
@internalsref{Music-expressions}, so you can also find which objects
to tweak by browsing the internals document.

@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} only apply to the first
following word; 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 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
* Vertical spacing::            
* Horizontal spacing::          
@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 @{
      \PianoStaffContext
      \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  @{
  \ScoreContext
  SpacingSpanner \override #'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.



@node Font Size
@section Font 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 smaller sizes
the font gets 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 feta20
@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
* 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}, @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 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 a 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, use the following Scheme code:
@example
        \paper@{
           #(set-paper-size "a4")
        @}
@end example


@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' consists of all
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.

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.