@c -*- coding: utf-8; mode: texinfo; -*-
@node Tweaking output
@chapter Tweaking output

This chapter discusses how to modify output.  LilyPond is extremely
configurable; virtually every fragment of output may be changed.


@menu
* Moving objects::              
* Fixing overlapping notation::  
* Common tweaks::               
* Default files::               
* Advanced tweaks with Scheme::  
@end menu


@node Moving objects
@section Moving objects

This may come as a surprise, but LilyPond is not perfect.  Some notation
elements can overlap.  This is unfortunate, but (in most cases) is easily
solved.

@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
e4^\markup{ \italic ritenuto } g b e
@end lilypond

@cindex padding

The easiest solution is to increase the distance between the object
(in this case text, but it could easily be fingerings or dynamics
instead) and the note.  In LilyPond, this is called the
@code{padding} property; it is measured in staff spaces.  For most
objects, this value is around 1.0 or less (it varies with each
object). We want to increase it, so let's try 1.5

@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
\once \override TextScript #'padding = #1.5
e4^\markup{ \italic ritenuto } g b e
@end lilypond

That looks better, but it isn't quite big enough.  After experimenting
with a few values, we think 2.3 is the best number in this case.  However,
this number is merely the result of experimentation and my personal
taste in notation.  Try the above example with 2.3... but also try higher
(and lower) numbers.  Which do you think looks the best?

The @code{staff-padding} property is closely related.  @code{padding}
controls the minimum amount of space between an object and the nearest
other object (generally the note or the staff lines);
@code{staff-padding} controls the minimum amount of space between an
object and the staff.  This is a subtle difference, but you can see
the behavior here.

@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
c4^"piu mosso" b a b
\once \override TextScript #'padding = #2.6
c4^"piu mosso" d e f
\once \override TextScript #'staff-padding = #2.6
c4^"piu mosso" fis a g
\break
c,,4^"piu mosso" b a b
\once \override TextScript #'padding = #2.6
c4^"piu mosso" d e f
\once \override TextScript #'staff-padding = #2.6
c4^"piu mosso" fis a g
@end lilypond

@cindex extra-offset

Another solution gives us complete control over placing the object -- we
can move it horizontally or vertically.  This is done with the
@code{extra-offset} property.  It is slightly more complicated and can
cause other problems.  When we move objects with @code{extra-offset},
the movement is done after LilyPond has placed all other objects.  This
means
that the result can overlap with other objects.

@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
\once \override TextScript #'extra-offset = #'( 1.0 . -1.0 )
e4^\markup{ \italic ritenuto } g b e
@end lilypond

With @code{extra-offset}, the first number controls the horizontal
movement (left is negative); the second number controls the vertical
movement (up is positive).  After a bit of experimenting, we decided
that these values look good

@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
\once \override TextScript #'extra-offset = #'( -1.6 . 1.0 )
e4^\markup{ \italic ritenuto } g b e
@end lilypond

@noindent
Again, these numbers are simply the result of a few experiments and
looking at the output.  You might prefer the text to be slightly higher,
or to the left, or whatever.  Try it and look at the result!

One final warning: in this section, we used

@example
\once \override TextScript @dots{}
@end example

This tweaks the display of text for the next note.  If the note has
no text, this tweak does nothing (and does @strong{not} wait until
the next bit of text).  To change the behavior of everything after
the command, omit the @code{\once}.  To stop this tweak, use a
@code{\revert}.  This is explained in depth in
@ref{The \override command}.

@lilypond[quote,fragment,ragged-right,verbatim,relative=3]
c4^"piu mosso" b
\once \override TextScript #'padding = #2.6
  a4 b
c4^"piu mosso" d e f
\once \override TextScript #'padding = #2.6
c4^"piu mosso" d e f
c4^"piu mosso" d e f
\break
\override TextScript #'padding = #2.6
c4^"piu mosso" d e f
c4^"piu mosso" d e f
\revert TextScript #'padding
c4^"piu mosso" d e f
@end lilypond

@seealso

This manual: @ref{The \override command}, @ref{Common tweaks}.


@node Fixing overlapping notation
@section Fixing overlapping notation

In @ref{Moving objects}, we saw how to move a @code{TextScript}
object.  The same mechanism can be used to move other types of
objects; simply replace @code{TextScript} with the name of
another object.

To find the object name, look at the ``@strong{see also}'' at
bottom of the relevant documentation page.  For example, at
the bottom of @ref{Dynamics}, we see

@quotation
@seealso

Program reference: @internalsref{DynamicText}, @internalsref{Hairpin}.
Vertical positioning of these symbols is handled by
@internalsref{DynamicLineSpanner}.
@end quotation

@noindent
So to move dynamics around vertically, we use

@example
\override DynamicLineSpanner #'padding = #2.0
@end example

We cannot list every object, but here is a list of the most
common objects.

@multitable @columnfractions .33 .66
@headitem Object type           @tab Object name
@item Dynamics (vertically)     @tab @code{DynamicLineSpanner}
@item Dynamics (horizontally)   @tab @code{DynamicText}
@item Ties                      @tab @code{Tie}
@item Slurs                     @tab @code{Slur}
@item Articulations             @tab @code{Script}
@item Fingerings                @tab @code{Fingering}
@item Text e.g. @code{^"text"}  @tab @code{TextScript}
@item Rehearsal / Text marks    @tab @code{RehearsalMark}
@end multitable


@node Common tweaks
@section Common tweaks

Some overrides are so common that predefined commands are provided as
short-cuts, such as @code{\slurUp} and @code{\stemDown}.  These
commands are described in the Notation Reference under the appropriate
sections.

The complete list of modifications available for each type of
object (like slurs or beams) are documented in the Program
Reference.  However, many layout objects share properties which can be
used to apply generic tweaks.

@itemize @bullet

@cindex padding

@item
The @code{padding} property can be set to increase
(or decrease) the distance between symbols that are printed
above or below notes.  This applies to all objects with
@code{side-position-interface}.

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

@lilypond[quote,fragment,relative=1,verbatim]
% This will not work, see below:
\override MetronomeMark #'padding = #3
\tempo 4=120
c1
% This works:
\override Score.MetronomeMark #'padding = #3
\tempo 4=80
d1
@end lilypond

Note in the second example how important it is to figure out what
context handles a certain object.  Since the @code{MetronomeMark} object
is handled in the @code{Score} context, property changes in the
@code{Voice} context will not be noticed.  For more details, see
@ref{Constructing a tweak}.

@cindex extra-offset

@item
The @code{extra-offset} property moves objects around
in the output; it requires a pair of numbers.  The first number
controls horizontal movement; a positive number will
move the object to the right.  The second number controls vertical
movement; a positive number will move it higher.  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:

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

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

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

@end itemize

@cindex Tweaks, distances
@cindex Distances

Distances in LilyPond are measured in staff-spaces, while most
thickness properties are measured in line-thickness.  Some
properties are different; for example, the thickness of beams
are measured in staff-spaces.  For more information, see the
relevant portion of the program reference.


@node Default files
@section Default files

The Program Reference documentation contains a lot of information
about LilyPond, but even more information can be gathered from
looking at the internal LilyPond files.

Some default settings (such as the definitions for
@code{\header@{@}}s) are stored as @code{.ly} files.  Other
settings (such as the definitions of markup commands) are
stored as @code{.scm} (Scheme) files.  Further explanation is
outside the scope of this manual; users should be warned that
a substantial amount of technical knowledge or time is required
to understand these files.

@itemize bullet

@item Linux: @file{@{INSTALLDIR@}/lilypond/usr/share/lilypond/current/}

@item OSX:
@file{@{INSTALLDIR@}/LilyPond.app/Contents/Resources/share/lilypond/current/}.
To access this, either @code{cd} into this directory from
the Terminal, or control-click on the LilyPond application
and select "Show Package Contents".

@item Windows: @file{@{INSTALLDIR@}/LilyPond/usr/share/lilypond/current/}

@end itemize

The @file{ly/} and @file{scm/} directories will be of
particular interest.  Files such as @file{ly/property-init.ly} and
@file{ly/declarations-init.ly} define all the common tweaks.


@node Advanced tweaks with Scheme
@section Advanced tweaks with Scheme

We have seen how LilyPond output can be heavily modified using
commands like
@code{\override TextScript #'extra-offset = ( 1 . -1)}.  But
we have even more power if we use Scheme.  For a full explantion
of this, see the @ref{Scheme tutorial} and
@ref{Interfaces for programmers}.

We can use Scheme to simply @code{\override} commands,

@lilypond[quote,verbatim,ragged-right]
padText = #(define-music-function (parser location padding) (number?)
#{
  \once \override TextScript #'padding = #$padding
#})

\relative c''' {
  c4^"piu mosso" b a b
  \padText #1.8
  c4^"piu mosso" d e f
  \padText #2.6
  c4^"piu mosso" fis a g
}
@end lilypond

We can use it to create new commands,

@lilypond[quote,verbatim,ragged-right]
tempoMark = #(define-music-function (parser location padding marktext)
                                    (number? string?)
#{
  \once \override Score . RehearsalMark #'padding = $padding
  \once \override Score . RehearsalMark #'no-spacing-rods = ##t
  \mark \markup { \bold $marktext }
#})

\relative c'' {
c2 e
\tempoMark #3.0 #"Allegro"
g c
}
@end lilypond

Even music expressions can be passed in.

@lilypond[quote,verbatim,ragged-right]
pattern = #(define-music-function (parser location x y) (ly:music? ly:music?)
#{
  $x e8 a b $y b a e
#})

\relative c''{
  \pattern c8 c8\f
  \pattern {d16 dis} { ais16-> b\p }
}
@end lilypond