[lilypond.git] / Documentation / notation / spacing.itely

@c -*- coding: utf-8; mode: texinfo; -*-

@ignore
    Translation of GIT committish: FILL-IN-HEAD-COMMITTISH

    When revising a translation, copy the HEAD committish of the
    version that you are working on.  For details, see the Contributors'
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@end ignore

@c \version "2.13.39"

@ignore
GDP TODO list

Negative numbers are allowed:
> Are you sure? The following works well
> \paper{
>   first-page-number = -2
> }
> and prints page number -1 on the second page, for example.


In 5.2.1 the @refbugs (line 495 in spacing.itely on master) it
states:

"@code{layout-set-staff-size} does not change the distance between
the
staff lines."

Could we add a sentence:
"Use instead the pair               fontSize = #@var{N}
            \override StaffSymbol #'staff-space = #(magstep
@var{N})
inside the Staff context to change the size of the font and the
distance between
staff lines accordingly."

Actually I found, that the @internalsref{StaffSymbol} at line 481
sends to an incomplete
documentation.  The property staff-space is not explained here.  I
thought Y-extent might be of
help, but it is in turn explained by x-space which again is
missing from the list.  Who has the
knowledge to fix this?


Clarify
http://code.google.com/p/lilypond/issues/detail?id=68

@end ignore


@node Spacing issues
@chapter Spacing issues

The global paper layout is 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.
This influences where line breaks are chosen, and thus ultimately, how
many pages a piece of music takes.

Globally speaking, this procedure happens in four steps: first,
flexible distances (@q{springs}) are chosen, based on durations.  All
possible line breaking combinations are tried, and a @q{badness} score
is calculated for each.  Then the height of each possible system is
estimated.  Finally, a page breaking and line breaking combination is chosen
so that neither the horizontal nor the vertical spacing is too cramped
or stretched.

Settings which influence layout may be placed in two blocks.
The @code{\paper @{...@}} block is placed outside any
@code{\score @{...@}} blocks and contains settings that
relate to the entire document.  The @code{\layout @{...@}}
block is placed within a @code{\score @{...@}} block and
contains settings for that particular score.  If you have
only one @code{\score @{...@}} block the two have the same
effect.  In general the commands shown in this chapter can
be placed in either.

@menu
* Paper and pages::
* Music layout::
* Breaks::
* Vertical spacing::
* Horizontal spacing::
* Fitting music onto fewer pages::
@end menu


@node Paper and pages
@section Paper and pages

This section deals with the boundaries that define the area
within which music can be printed.

@menu
* Paper size::
* Page formatting::
@end menu


@node Paper size
@subsection Paper size

@cindex paper size
@cindex page size

Two functions are available for changing the paper size:
@code{set-default-paper-size} and @code{set-paper-size}.
@code{set-default-paper-size} must be placed in the toplevel
scope, and @code{set-paper-size} must be placed in a @code{\paper}
block:

@example
#(set-default-paper-size "a4")
@end example

@example
\paper @{
  #(set-paper-size "a4")
@}
@end example

@noindent
@code{set-default-paper-size} sets the size of all pages, whereas
@code{set-paper-size} only sets the size of the pages that the
@code{\paper} block applies to.  For example, if the @code{\paper}
block is at the top of the file, then it will apply the paper size
to all pages.  If the @code{\paper} block is inside a
@code{\book}, then the paper size will only apply to that book.

Common paper sizes are available, including @code{a4},
@code{letter}, @code{legal}, and @code{11x17} (also known as
tabloid).  Many more paper sizes are supported by default.  For
details, see @file{scm/@/paper@/.scm}, and search for the
definition of @code{paper-alist}.

@c TODO add a new appendix for paper sizes (auto-generated) -pm

@warning{The default paper size is @code{a4}.}

Extra sizes may be added by editing the definition of
@code{paper-alist} in the initialization file
@file{scm/@/paper@/.scm}, however they will be overridden on a
subsequent install.

@cindex orientation
@cindex landscape

If the symbol @code{'landscape} is supplied as an argument to
@code{set-default-paper-size}, pages will be rotated by 90
degrees, and wider line widths will be set accordingly.

@example
#(set-default-paper-size "a6" 'landscape)
@end example

Setting the paper size will adjust a number of @code{\paper}
variables, such as margins.  To use a particular paper size with
altered @code{\paper} variables, set the paper size before setting
the variables.


@seealso
Installed Files:
@file{scm/@/paper@/.scm}.

Snippets:
@rlsr{Spacing}.


@node Page formatting
@subsection Page formatting

@funindex \paper

Margins, headers, and footers and other layout variables are
automatically set according to the paper size.

Default margin values are accessible in
@file{ly/@/paper@/-defaults@/-init@/.ly}.  They apply to the default
paper size (a4, unless specified differently) and are scaled
accordingly for other paper sizes.

This section lists and describes a number of paper variables that
may be altered.

@menu
* Fixed vertical dimensions::
* Flexible vertical dimensions::
* Horizontal dimensions::
* Other layout variables::
@end menu


@node Fixed vertical dimensions
@unnumberedsubsubsec Fixed vertical dimensions

@table @code
@item paper-height
@funindex paper-height

The height of the page.  Default: the height of the current paper
size.  For details, see @ref{Paper size}.

@item top-margin
@funindex top-margin

The margin between the top of the page and the top of the
printable area.  Default: @code{5\mm}.

@item bottom-margin
@funindex bottom-margin

The margin between the bottom of the printable area and the bottom
of the page.  Default: @code{6\mm}.
@end table


@node Flexible vertical dimensions
@unnumberedsubsubsec Flexible vertical dimensions

In most cases, it is preferable for the vertical distances between
certain items (such as margins, titles, systems, and separate
scores) to be flexible, so that they stretch and compress nicely
according to each situation.  A number of @code{\paper} variables
(listed below) are available to fine-tune the stretching behavior
of these dimensions.

Note that the @code{\paper} variables discussed in this section do
not control the spacing of staves within individual systems.
Within-system spacing is controlled by grob properties, with
settings typically entered inside a @code{\score} or @code{layout}
block, and not inside a @code{\paper} block.  See
@ref{Flexible vertical spacing within systems}.


@subsubheading Structure of spacing alists for @code{\paper} variables

Each of these variables is an alist (association list) containing
four @emph{keys}:

@itemize
@item @code{padding} -- the minimum required amount of
unobstructed vertical whitespace between two items, measured in
staff-spaces.  This can be thought of as the minimum height of an
unobstructed (invisible) rectangle that extends from the leftmost
to the rightmost point of the combined items.

@item @code{space} -- the default vertical distance, measured in
staff-spaces, between the @emph{reference points} of the two
items, when no collisions would result, and no stretching or
compressing is in effect.  The reference point of a (title or
top-level) markup is its highest point, and the reference point of
a system is the vertical center of the nearest @code{StaffSymbol}
-- even if a non-staff line (such as a @code{Lyrics} context) is
in the way.  Values for @code{space} that are less than either
@code{padding} or @code{minimum-distance} are not meaningful,
since the resulting distance will never be less than either
@code{padding} or @code{minimum-distance}.

@item @code{minimum-distance} -- the minimum required vertical
distance, measured in staff-spaces, between the reference points
of the two items, when compressing is in effect.  Values for
@code{minimum-distance} that are less than @code{padding} are not
meaningful, since the resulting distance will never be less than
@code{padding.}

@item @code{stretchability} -- a unitless measure of the
dimension's relative propensity to stretch.  If zero, the distance
will not stretch (unless collisions would result).  When positive,
the significance of a particular dimension's @code{stretchability}
value lies only in its relation to the @code{stretchability}
values of the other dimensions.  For example, if one dimension has
twice the @code{stretchability} of another, it will stretch twice
as easily.  Values should be non-negative and finite.  The value
@code{+inf.0} triggers a @code{programming_error} and is ignored,
but @code{1.0e7} can be used for an almost infinitely stretchable
spring.  If unset, the default value is set to @code{space}.  Note
that the dimension's propensity to @emph{compress} cannot be
directly set by the user and is equal to
(@code{space}@tie{}@minus{}@tie{}@code{minimum-distance}).
@end itemize

If a page has a ragged bottom, the resulting distance is the
largest of:

@itemize
@item @code{space},
@item @code{minimum-distance}, and
@item @code{padding} plus the smallest distance necessary to
eliminate collisions.
@end itemize

Specific methods for modifying alists are discussed in
@ref{Modifying alists}.  The flexible vertical @code{\paper}
dimensions variables can only be set within a @code{\paper} block.

The following example demonstrates the two ways these alists can
be modified.  The first declaration updates one key-value
individually, and the second complete re-defines the variable:

@example
\paper @{
  system-system-spacing #'space = #8

  score-system-spacing =
    #'((padding . 1)
       (space . 12)
       (minimum-distance . 6)
       (stretchability . 12))
@}
@end example

The initialized default settings for these variables are defined
in @file{ly/paper-defaults-init.ly}.


@subsubheading Flexible vertical dimension @code{\paper} variables

The names of these variables follow the format
@code{@var{upper}-@var{lower}-spacing}, where @code{@var{upper}}
and @code{@var{lower}} are the items to be spaced.  Each distance
is measured between the reference points of the two items (see the
description of the alist structure above).  Note that in these
variable names, the term @q{@code{markup}} refers to both
@emph{title markups} (@code{bookTitleMarkup} or
@code{scoreTitleMarkup}) and @emph{top-level markups} (see
@ref{File structure}).

@table @code
@item markup-system-spacing
@funindex markup-system-spacing

the distance between a (title or top-level) markup and the system
that follows it.

@item score-markup-spacing
@funindex score-markup-spacing

the distance between the last system of a score and the (title or
top-level) markup that follows it.

@item score-system-spacing
@funindex score-system-spacing

the distance between the last system of a score and the first
system of the score that follows it, when no (title or top-level)
markup exists between them.

@item system-system-spacing
@funindex system-system-spacing

the distance between two systems in the same score.

@item markup-markup-spacing
@funindex markup-markup-spacing

the distance between two (title or top-level) markups.

@item last-bottom-spacing
@funindex last-bottom-spacing

the distance from the last system or top-level markup on a page to
the bottom of the printable area (i.e. the top of the bottom
margin).

@item top-system-spacing
@funindex top-system-spacing

the distance from the top of the printable area (i.e. the bottom
of the top margin) to the first system on a page, when there is no
(title or top-level) markup between the two.

@item top-markup-spacing
@funindex top-markup-spacing

the distance from the top of the printable area (i.e. the bottom
of the top margin) to the first (title or top-level) markup on a
page, when there is no system between the two.
@end table


@snippets

The header and footer are created by the functions
@code{make-footer} and @code{make-header}, defined in
@code{\paper}.  The default implementations are in
@file{ly/paper-defaults.ly} and @file{ly/titling-init.ly}.

The page layout itself is done by two functions in the
@code{\paper} block, @code{page-music-height} and
@code{page-make-stencil}.  The former tells the line-breaking
algorithm how much space can be spent on a page, the latter
creates the actual page given the system to put on it.

You can define @code{\paper} block values in Scheme.  In that case
@code{mm}, @code{in}, @code{pt}, and @code{cm} are variables
defined in @file{paper-defaults.ly} with values in millimeters.
That is why the value @w{@code{2 cm}} must be multiplied in the
example:

@example
\paper @{
 #(define bottom-margin (* 2 cm))
@}
@end example


Example:

@example
\paper @{
  paper-width = 2\cm
  top-margin = 3\cm
  bottom-margin = 3\cm
  ragged-last-bottom = ##t
@}
@end example

This second example centers page numbers at the bottom of every page.

@example
\paper @{
  print-page-number = ##t
  print-first-page-number = ##t
  oddHeaderMarkup = \markup \fill-line @{ " " @}
  evenHeaderMarkup = \markup \fill-line @{ " " @}
  oddFooterMarkup = \markup @{ \fill-line @{
     \bold \fontsize #3 \on-the-fly #print-page-number-check-first
     \fromproperty #'page:page-number-string @} @}
  evenFooterMarkup = \markup @{ \fill-line @{
     \bold \fontsize #3 \on-the-fly #print-page-number-check-first
     \fromproperty #'page:page-number-string @} @}
@}
@end example

@seealso
Notation Reference:
@ref{Flexible vertical spacing within systems}.

Snippets:
@rlsr{Spacing}.


@node Horizontal dimensions
@unnumberedsubsubsec Horizontal dimensions


There are a few variables that determine the horizontal dimensions
on a page:

@table @code

@item binding-offset
@funindex binding-offset

The amount @code{inner-margin} is increased
to make sure nothing will be hidden by the binding.
Works only with @code{two-sided} set to true.  Default:
@code{0}.

@item horizontal-shift
@funindex horizontal-shift

The amount that all systems (including titles and system
separators) are shifted to the right.  Default: @code{0.0}.

@item indent
@funindex indent

The level of indentation for the first system in a score.
Default: @code{15\mm}.

@item inner-margin
@funindex inner-margin

The margin all pages have at the inner side if they are part
of a book.  Works only with @code{two-sided} set to true.
Default: @code{10\mm}.

@item left-margin
@funindex left-margin

The margin between the left edge of the page and the beginning of
each system.  Default: @code{10\mm}.

@item line-width
@funindex line-width

The width of music systems.  Default: @code{paper-width} minus
@code{left-margin} and @code{right-margin}.

@item outer-margin
@funindex outer-margin

The margin all pages have at the outer side if they are part
of a book.  Works only with @code{two-sided} set to true.
Default: @code{20\mm}.

@item paper-width
@funindex paper-width

The width of the page.  Default: the width of the current paper
size.  For details, see @ref{Paper size}.

@item right-margin
@funindex right-margin

The margin between the right edge of the page and the end of
each system.  Default: @code{10\mm}.

@item short-indent
@funindex short-indent

The level of indentation for all systems in a score besides the
first system.  Default: @code{0}.

@end table

If some values are not set, defaults will be taken.  Their exact
value is adjusted, depending on the paper size specified.  Currently,
the following values are affected by this scaling:

@itemize
@item @var{left-margin}
@item @var{right-margin}
@item @var{top-margin}
@item @var{bottom-margin}
@item @var{head-separation}
@item @var{foot-separation}
@item @var{indent}
@item @var{short-indent}
@end itemize

The settings for @code{line-width}, @code{left-margin},
@code{right-margin} and @code{paper-width} depend on
each other, but they do not have to be specified
completely.

@example
\paper @{
  left-margin = 30\mm
@}
@end example

In this example, only @code{left-margin} is set.  The value for
@code{right-margin} will remain default, @code{line-width} is
calculated automatically.

@example
\paper @{
  line-width = 150\mm
@}
@end example

Here @code{left-margin} and @code{right-margin} will be set
to the same value.  Therefore, @code{line-width} is subtracted
from @code{paper-width} and divided by two.  That means systems
are centered on the page, if only @code{line-width} is
specified.

Some checks occur to ensure the values are set correctly.
If the values do not match or systems would run off the page,
a warning is printed and default values are set.

@example
\paper @{
  paper-width = 210\mm
  left-margin = 20\mm
  right-margin = 30\mm
  line-width = 100\mm
@}
@end example

These checks can be avoided by setting @code{check-consistency}
to false.

@example
\paper @{
  paper-width = 210\mm
  left-margin = 20\mm
  line-width = 200\mm
  check-consistency = ##f
@}
@end example

@warning{If @code{paper-width} is manually set, @code{line-width},
@code{left-margin}, @code{indent}, and @code{short-indent} may
have to be adjusted as well.}

@seealso
Snippets:
@rlsr{Spacing}.



@node Other layout variables
@unnumberedsubsubsec Other layout variables

These variables can be used to adjust page layout in general.

@table @code

@item auto-first-page-number
@funindex auto-first-page-number

The page breaking algorithm is affected by the first page number
being odd or even.  If set to true, the page breaking algorithm
will decide whether to start with an odd or even number.  This
will result in the first page number remaining as is or being
increased by one.  Default: @code{##f}.

@ignore

TODO: this variable is used, but I don't know what it does. -pm
@item blank-after-score-page-force
@funindex blank-after-score-page-force

Default: @code{2}.

@end ignore

@item blank-last-page-force
@funindex blank-last-page-force

The penalty for ending the score on an odd-numbered page.
Default: @code{0}.

@item blank-page-force
@funindex blank-page-force

The penalty for having a blank page in the middle of a
score.  This is not used by @code{ly:optimal-breaking} since it will
never consider blank pages in the middle of a score.  Default:
@code{5}.

@item check-consistency
@funindex check-consistency

If set to true, check whether @code{left-margin}, @code{right-margin} and
@code{line-width} fit each other.  Also make sure that their combination
does not exceed the available @code{paper-width}.  Default: @code{##t}.

@item first-page-number
@funindex first-page-number

The value of the page number on the first page.  Default:
@code{#1}.

@item max-systems-per-page
@funindex max-systems-per-page

The maximum number of systems that will be placed on a page.  This
is currently supported only by the @code{ly:optimal-breaking} algorithm.
Default: unset.

@item min-systems-per-page
@funindex min-systems-per-page

The minimum number of systems that will be placed on a page.  This
may cause pages to be overfilled if it is made too large.  This is
currently supported only by the @code{ly:optimal-breaking} algorithm.
Default: unset.

@item page-breaking-system-system-spacing
@funindex page-breaking-system-system-spacing

Tricks the page breaker into thinking that
@code{system-system-spacing} is set to something different than
it really is.  For example, if
@code{page-breaking-system-system-spacing #'padding} is set to something
substantially larger than @code{system-system-spacing #'padding}, then the
page-breaker will put fewer systems on each page.  Default: unset.

@item page-count
@funindex page-count

The number of pages to be used for a score.  Default: unset.

@item page-spacing-weight
@funindex page-spacing-weight

The relative importance of page (vertical) spacing and line
(horizontal) spacing.  High values will make page spacing more
important.  Default: @code{#10}.

@item print-all-headers
@funindex print-all-headers

If set to true, this will print all headers for each \score in the
output.  Normally only the piece and opus header variables are
printed.  Default: @code{##f}.

@item print-first-page-number
@funindex print-first-page-number

If set to true, a page number is printed on the first page.
Default: @code{##f}.

@item print-page-number
@funindex print-page-number

If set to false, page numbers are not printed.  Default:
@code{##t}.

@item ragged-bottom
@funindex ragged-bottom

If set to true, systems will not spread vertically across the
page.  This does not affect the last page.  Default: @code{##f}.

This should be set to true for pieces that have only two or three
systems per page, for example orchestral scores.

@item ragged-last
@funindex ragged-last

If set to true, the last system in the score will not fill the
line width.  Instead the last system ends at its natural
horizontal length.  Default: @code{##f}.

@item ragged-last-bottom
@funindex ragged-last-bottom

If set to false, systems will spread vertically across the last
page.  Default: @code{##t}.

Pieces that amply fill two pages or more should have this set to
true.

It also affects the last page of book parts, ie parts of a book created
with @code{\bookpart} blocks.

@item ragged-right
@funindex ragged-right

If set to true, systems will not fill the line width.  Instead,
systems end at their natural horizontal length.  Default:
@code{##f}.

If the score has only one system, the default value is @code{##t}.

@item system-separator-markup
@funindex system-separator-markup

A markup object that is inserted between systems.  This is often
used for orchestral scores.  Default: unset.

The markup command @code{\slashSeparator} is provided as a sensible
default,  for example

@lilypond[quote,ragged-right]
#(set-default-paper-size "a6" 'landscape)
\book {
  \score {
    \relative c' { c1 \break c1 }
  }
  \paper {
    system-separator-markup = \slashSeparator
  }
}
@end lilypond

@item system-count
@funindex system-count

The number of systems to be used for a score.
Default: unset.

@item systems-per-page
@funindex systems-per-page

The number of systems that should be placed on each page.
This is currently supported only by the @code{ly:optimal-breaking} algorithm.
Default: unset.

@item two-sided
@funindex two-sided

@cindex gutter
@cindex binding gutter

If set to true, use @code{inner-margin}, @code{outer-margin} and
@code{binding-offset} to determine margins depending on whether
the page number is odd or even.  This overrides @code{left-margin}
and @code{right-margin}.  Default: @code{##f}.

@end table


@seealso
Snippets:
@rlsr{Spacing}.


@knownissues

The default page header puts the page number and the @code{instrument}
field from the @code{\header} block on a line.

The titles (from the @code{\header@{@}} section) are treated as a
system, so @code{ragged-bottom} and @code{ragged-last-bottom} will
add space between the titles and the first system of the score.


@node Music layout
@section Music layout

@menu
* Setting the staff size::
* Score layout::
@end menu


@node Setting the staff size
@subsection Setting the staff size

@cindex font size, setting
@cindex staff size, setting
@funindex layout file

The default @strong{staff size} is set to 20 points.
This may be changed in two ways:

To set the staff size globally for all scores in a file (or
in a @code{book} block, to be precise), use @code{set-global-staff-size}.

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

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

To set the staff size individually for each score, use
@example
\score@{
  ...
  \layout@{
  #(layout-set-staff-size 15)
  @}
@}
@end example

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:

@quotation
@multitable @columnfractions .15 .2 .22 .2

@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 20
@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
@end quotation

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


@seealso
Notation Reference:
@ref{Selecting notation font size}.

Snippets:
@rlsr{Spacing}.


@knownissues

@code{layout-set-staff-size} does not change the distance between the
staff lines.


@node Score layout
@subsection Score layout

@funindex \layout

While @code{\paper} contains settings that relate to the page formatting
of the whole document, @code{\layout} contains settings for score-specific
layout.

@example
\layout @{
  indent = 2.0\cm
  \context @{ \Voice
    \override TextScript #'padding = #1.0
    \override Glissando #'thickness = #3
  @}
@}
@end example


@seealso
Notation Reference:
@ref{Changing context default settings}.

Snippets:
@rlsr{Spacing}.


@node Breaks
@section Breaks

@menu
* Line breaking::
* Page breaking::
* Optimal page breaking::
* Optimal page turning::
* Minimal page breaking::
* Explicit breaks::
* Using an extra voice for breaks::
@end menu


@node Line breaking
@subsection Line breaking

@cindex line breaks
@cindex breaking lines

Line breaks are normally determined automatically.  They are chosen
so that lines look neither cramped nor loose, and 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.  However,
line breaks can only occur at the end of @q{complete} bars, i.e.,
where there are no notes or tuplets left @q{hanging} over the bar
line.  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 ""},
although again there must be no notes left hanging over in any of
the staves at this point, or it will be ignored.

The opposite command, @code{\noBreak}, forbids a line break at the
bar line where it is inserted.

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

If @code{ragged-right} is set to true in the @code{\layout} block,
then systems end at their natural horizontal length, instead of
being spread horizontally to fill the whole line.  This is useful
for short fragments, and for checking how tight the natural
spacing is.

@c TODO Check and add para on default for ragged-right

The option @code{ragged-last} is similar to @code{ragged-right},
but affects only the last line of the piece.

@example
\layout @{
indent = #0
line-width = #150
ragged-last = ##t
@}
@end example



@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}.  For example, this would
cause the following 28 measures (assuming 4/4 time) to be broken
every 4 measures, and only there:

@example
<< \repeat unfold 7 @{
         s1 \noBreak s1 \noBreak
         s1 \noBreak s1 \break @}
   @emph{the real music}
>>
@end example

@c TODO Check this
A linebreaking configuration can be saved as a @code{.ly} file
automatically.  This allows vertical alignments to be stretched to
fit pages in a second formatting run.  This is fairly new and
complicated.  More details are available in
@rlsr{Spacing}.


@predefined
@funindex \break
@code{\break},
@funindex \noBreak
@code{\noBreak}.
@endpredefined


@seealso
Internals Reference:
@rinternals{LineBreakEvent}.

Snippets:
@rlsr{Spacing}.


@knownissues

Line breaks can only occur if there is a @q{proper} bar line.  A note
which is hanging over a bar line is not proper, such as

@lilypond[quote,ragged-right,relative=2,verbatim]
c4 c2 << c2 {s4 \break } >>  % this does nothing
c2 c4 |           % a break here would work
c4 c2 c4 ~ \break % as does this break
c4 c2 c4
@end lilypond

This can be avoided by removing the @code{Forbid_line_break_engraver}.
Note that manually forced line breaks have to be added in parallel
with the music.

@lilypond[quote,ragged-right,verbatim]
\new Voice \with {
  \remove Forbid_line_break_engraver
} {
  c4 c2 << c2 {s4 \break } >>  % now the break is allowed
  c2 c4
}
@end lilypond

Similarly, line breaks are normally forbidden when beams cross bar
lines.  This behavior can be changed by setting
@code{\override Beam #'breakable = ##t}.


@node Page breaking
@subsection Page breaking

The default page breaking may be overridden by inserting
@code{\pageBreak} or @code{\noPageBreak} commands.  These commands are
analogous to @code{\break} and @code{\noBreak}.  They should be
inserted at a bar line.  These commands force and forbid a page-break
from happening.  Of course, the @code{\pageBreak} command also forces
a line break.

The @code{\pageBreak} and @code{\noPageBreak} commands may also be
inserted at top-level, between scores and top-level markups.

There are also analogous settings to @code{ragged-right} and
@code{ragged-last} which have the same effect on vertical spacing:
@code{ragged-bottom} and @code{ragged-last-bottom}.  If set to
@code{##t} the systems on all pages or just the last page
respectively will not be justified vertically.

For more details see @ref{Vertical spacing}.

Page breaks are computed by the @code{page-breaking} function.  LilyPond
provides three algorithms for computing page breaks,
@code{ly:optimal-breaking}, @code{ly:page-turn-breaking} and
@code{ly:minimal-breaking}.  The default is @code{ly:optimal-breaking},
but the value can be changed in the @code{\paper} block:

@example
\paper@{
  #(define page-breaking ly:page-turn-breaking)
@}
@end example

@funindex \bookpart

When a book has many scores and pages, the page breaking problem may be
difficult to solve, requiring large processing time and memory.  To ease
the page breaking process, @code{\bookpart} blocks are used to divide
the book into several parts: the page breaking occurs separately on each
part.  Different page breaking functions may also be used in different
book parts.

@example
\bookpart @{
  \header @{
    subtitle = "Preface"
  @}
  \paper @{
     %% In a part consisting mostly of text,
     %% ly:minimal-breaking may be preferred
     #(define page-breaking ly:minimal-breaking)
  @}
  \markup @{ @dots{} @}
  @dots{}
@}
\bookpart @{
  %% In this part, consisting of music, the default optimal
  %% page breaking function is used.
  \header @{
    subtitle = "First movement"
  @}
  \score @{ @dots{} @}
  @dots{}
@}
@end example


@predefined
@funindex \pageBreak
@code{\pageBreak},
@funindex \noPageBreak
@code{\noPageBreak}.
@endpredefined


@seealso
Snippets:
@rlsr{Spacing}.


@node Optimal page breaking
@subsection Optimal page breaking

@funindex ly:optimal-breaking

The @code{ly:optimal-breaking} function is LilyPond's default method of
determining page breaks.  It attempts to find a page breaking that minimizes
cramping and stretching, both horizontally and vertically.  Unlike
@code{ly:page-turn-breaking}, it has no concept of page turns.


@seealso
Snippets:
@rlsr{Spacing}.


@node Optimal page turning
@subsection Optimal page turning

@funindex ly:page-turn-breaking

Often it is necessary to find a page breaking configuration so that there is
a rest at the end of every second page.  This way, the musician can turn the
page without having to miss notes.  The @code{ly:page-turn-breaking} function
attempts to find a page breaking minimizing cramping and stretching, but with
the additional restriction that it is only allowed to introduce page turns
in specified places.

There are two steps to using this page breaking function.  First, you
must enable it in the @code{\paper} block, as explained in @ref{Page
breaking}.  Then you must tell the function where you would like to allow
page breaks.

There are two ways to achieve the second step.  First, you can specify each
potential page turn manually, by inserting @code{\allowPageTurn} into your
input file at the appropriate places.

If this is too tedious, you can add a @code{Page_turn_engraver} to a Staff or
Voice context.  The @code{Page_turn_engraver} will scan the context for
sections without notes (note that it does not scan for rests; it scans for
the absence of notes.  This is so that single-staff polyphony with rests in one
of the parts does not throw off the @code{Page_turn_engraver}).  When it finds
a sufficiently long section without notes, the @code{Page_turn_engraver} will
insert an @code{\allowPageTurn} at the final bar line in that section, unless
there is a @q{special} bar line (such as a double bar), in which case the
@code{\allowPageTurn} will be inserted at the final @q{special} bar line in
the section.

@funindex minimumPageTurnLength
The @code{Page_turn_engraver} reads the context property
@code{minimumPageTurnLength} to determine how long a note-free section must
be before a page turn is considered.  The default value for
@code{minimumPageTurnLength} is @code{#(ly:make-moment 1 1)}.  If you want
to disable page turns, you can set it to something very large.

@example
\new Staff \with @{ \consists "Page_turn_engraver" @}
@{
  a4 b c d |
  R1 | % a page turn will be allowed here
  a4 b c d |
  \set Staff.minimumPageTurnLength = #(ly:make-moment 5 2)
  R1 | % a page turn will not be allowed here
  a4 b r2 |
  R1*2 | % a page turn will be allowed here
  a1
@}
@end example

@funindex minimumRepeatLengthForPageTurn
The @code{Page_turn_engraver} detects volta repeats.  It will only allow a page
turn during the repeat if there is enough time at the beginning and end of the
repeat to turn the page back.  The @code{Page_turn_engraver} can also disable
page turns if the repeat is very short.  If you set the context property
@code{minimumRepeatLengthForPageTurn} then the @code{Page_turn_engraver} will
only allow turns in repeats whose duration is longer than this value.

The page turning commands, @code{\pageTurn}, @code{\noPageTurn} and
@code{\allowPageTurn}, may also be used at top-level, between scores and
top-level markups.


@predefined
@funindex \pageTurn
@code{\pageTurn},
@funindex \noPageTurn
@code{\noPageTurn},
@funindex \allowPageTurn
@code{\allowPageTurn}.
@endpredefined


@seealso
Snippets:
@rlsr{Spacing}.


@knownissues

There should only be one @code{Page_turn_engraver} in a score.  If there is more
than one, they will interfere with each other.


@node Minimal page breaking
@subsection Minimal page breaking

@funindex ly:minimal-breaking

The @code{ly:minimal-breaking} function performs minimal computations to
calculate the page breaking: it fills a page with as many systems as
possible before moving to the next one.  Thus, it may be preferred for
scores with many pages, where the other page breaking functions could be
too slow or memory demanding, or a lot of texts.  It is enabled using:

@example
\paper @{
  #(define page-breaking ly:minimal-breaking)
@}
@end example


@seealso
Snippets:
@rlsr{Spacing}.


@node Explicit breaks
@subsection Explicit breaks

Lily sometimes rejects explicit @code{\break} and @code{\pageBreak}
commands.  There are two commands to override this behavior:

@example
\override NonMusicalPaperColumn #'line-break-permission = ##f
\override NonMusicalPaperColumn #'page-break-permission = ##f
@end example

When @code{line-break-permission} is overridden to false, Lily will insert
line breaks at explicit @code{\break} commands and nowhere else.  When
@code{page-break-permission} is overridden to false, Lily will insert
page breaks at explicit @code{\pageBreak} commands and nowhere else.

@lilypond[quote,verbatim]
\paper {
  indent = #0
  ragged-right = ##t
  ragged-bottom = ##t
}

\score {
  \new Staff {
    \repeat unfold 2 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 4 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 6 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 8 { c'8 c'8 c'8 c'8 } \pageBreak
    \repeat unfold 8 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 6 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 4 { c'8 c'8 c'8 c'8 } \break
    \repeat unfold 2 { c'8 c'8 c'8 c'8 }
    }
  \layout {
    \context {
      \Score
      \override NonMusicalPaperColumn #'line-break-permission = ##f
      \override NonMusicalPaperColumn #'page-break-permission = ##f
    }
  }
}
@end lilypond


@seealso
Snippets:
@rlsr{Spacing}.


@node Using an extra voice for breaks
@subsection Using an extra voice for breaks

Line- and page-breaking information usually appears within note entry directly.

@example
\score @{
  \new Staff @{
    \repeat unfold 2 @{ c'4 c'4 c'4 c'4 @}
    \break
    \repeat unfold 3 @{ c'4 c'4 c'4 c'4 @}
  @}
@}
@end example

This makes @code{\break} and @code{\pageBreak} commands easy to enter but mixes
music entry with information that specifies how music should lay out
on the page.  You can keep music entry and line- and page-breaking
information in two separate places by introducing an extra voice to
contain the  breaks.  This extra voice
contains only skips together with @code{\break}, @code{pageBreak} and other
breaking layout information.

@lilypond[quote,verbatim]
\score {
  \new Staff <<
    \new Voice {
      s1 * 2 \break
      s1 * 3 \break
      s1 * 6 \break
      s1 * 5 \break
    }
    \new Voice {
      \repeat unfold 2 { c'4 c'4 c'4 c'4 }
      \repeat unfold 3 { c'4 c'4 c'4 c'4 }
      \repeat unfold 6 { c'4 c'4 c'4 c'4 }
      \repeat unfold 5 { c'4 c'4 c'4 c'4 }
    }
  >>
}
@end lilypond

This pattern becomes especially helpful when overriding
@code{line-break-system-details} and the other useful but long properties of
@code{NonMusicalPaperColumnGrob}, as explained in @ref{Vertical spacing}.

@lilypond[quote,verbatim]
\score {
  \new Staff <<
    \new Voice {
      \overrideProperty "Score.NonMusicalPaperColumn"
        #'line-break-system-details #'((Y-offset . 0))
      s1 * 2 \break

      \overrideProperty "Score.NonMusicalPaperColumn"
        #'line-break-system-details #'((Y-offset . 35))
      s1 * 3 \break

      \overrideProperty "Score.NonMusicalPaperColumn"
        #'line-break-system-details #'((Y-offset . 70))
      s1 * 6 \break

      \overrideProperty "Score.NonMusicalPaperColumn"
        #'line-break-system-details #'((Y-offset . 105))
      s1 * 5 \break
    }
    \new Voice {
      \repeat unfold 2 { c'4 c'4 c'4 c'4 }
      \repeat unfold 3 { c'4 c'4 c'4 c'4 }
      \repeat unfold 6 { c'4 c'4 c'4 c'4 }
      \repeat unfold 5 { c'4 c'4 c'4 c'4 }
    }
  >>
}
@end lilypond


@seealso
Notation Reference:
@ref{Vertical spacing}.

Snippets:
@rlsr{Spacing}.


@node Vertical spacing
@section Vertical spacing

@cindex vertical spacing
@cindex spacing, vertical

Vertical spacing is controlled by three things: the amount of
space available (i.e., paper size and margins), the amount of
space between systems, and the amount of space between
staves inside a system.

@menu
* Flexible vertical spacing within systems::
* Explicit staff and system positioning::
* Vertical collision avoidance::
@end menu


@node Flexible vertical spacing within systems
@subsection Flexible vertical spacing within systems

@cindex distance between staves
@cindex staff distance
@cindex space between staves
@cindex space inside systems

Three separate mechanisms control the flexible vertical spacing
within systems, one for each of the following categories:

@itemize
@item @emph{ungrouped staves},
@item @emph{grouped staves} (staves within a staff-group such as
@code{ChoirStaff}, etc.), and
@item @emph{non-staff lines} (such as @code{Lyrics},
@code{ChordNames}, etc.).
@end itemize

@c TODO: Clarify this.  This almost implies that non-staff lines
@c       have NO effect on the spacing between staves.  -mp

The height of each system is determined in two steps.  First, all
of the staves are spaced according to the amount of space
available.  Then, the non-staff lines are distributed between the
staves.

Note that the spacing mechanisms discussed in this section only
control the vertical spacing of staves and non-staff lines within
individual systems.  The vertical spacing between separate
systems, scores, markups, and margins is controlled by
@code{\paper} variables, which are discussed in
@ref{Flexible vertical dimensions}.

@menu
* Within-system spacing properties::
* Spacing of ungrouped staves::
* Spacing of grouped staves::
* Spacing of non-staff lines::
@end menu


@node Within-system spacing properties
@unnumberedsubsubsec Within-system spacing properties

The within-system vertical spacing mechanisms are controlled by
two sets of grob properties.  The first set is associated with the
@code{VerticalAxisGroup} grob, which is created by all staves and
non-staff lines.  The second set is associated with the
@code{StaffGrouper} grob, which can be created by staff-groups,
but only if explicitly called.  These properties are described
individually at the end of this section.

The names of these properties (except for @code{staff-affinity})
follow the format @code{@var{item1}-@var{item2}-spacing}, where
@code{@var{item1}} and @code{@var{item2}} are the items to be
spaced.  Note that @code{@var{item2}} is not necessarily below
@code{@var{item1}}; for example,
@code{nonstaff-relatedstaff-spacing} will measure upwards from the
non-staff line if @code{staff-affinity} is @code{#UP}.

Each distance is measured between the @emph{reference points} of
the two items.  The reference point for a staff is the vertical
center of its @code{StaffSymbol} (i.e. the middle line if
@code{line-count} is odd; the middle space if @code{line-count} is
even).  The reference points for individual non-staff lines are
given in the following table:

@multitable {Non-staff line} {Reference point}
@headitem Non-staff line @tab Reference point
@item @code{ChordNames}  @tab baseline
@item @code{NoteNames}   @tab baseline
@item @code{Lyrics}      @tab baseline
@item @code{Dynamics}    @tab vertical center
@item @code{FiguredBass} @tab highest point
@item @code{FretBoards}  @tab top line
@end multitable

In the following image, horizontal lines indicate the positions
of these reference points:

@lilypond[quote,noragged-right,line-width=110\mm]
#(define zero-space '((padding . -inf.0) (space . 0)))

alignToZero = \with {
  \override VerticalAxisGroup #'nonstaff-relatedstaff-spacing = #zero-space
  \override VerticalAxisGroup #'nonstaff-nonstaff-spacing = #zero-space
}
lowerCaseChords = \with {
  chordNameLowercaseMinor = ##t
}
staffAffinityDown = \with {
  \override VerticalAxisGroup #'staff-affinity = #DOWN
}
labelContext =
#(define-music-function
     (parser location context)
     (string?)
   #{ s1*0^\markup { \typewriter $context } #})

\layout {
  \context { \Dynamics    \alignToZero }
  \context { \FiguredBass \alignToZero }
  \context { \Lyrics      \alignToZero }
  \context { \NoteNames   \alignToZero }
  \context { \ChordNames  \alignToZero \lowerCaseChords }
  \context { \FretBoards  \alignToZero \staffAffinityDown }
  \context { \Score
    \override BarLine #'stencil = ##f
    \override DynamicText #'self-alignment-X = #-1
    \override FretBoard #'X-offset = #1.75
    \override InstrumentName #'minimum-Y-extent = #'(-2 . 2)
    \override InstrumentName #'extra-offset = #'(0 . -0.5)
    \override TextScript #'minimum-Y-extent = #'(-2 . 3)
    \override TimeSignature #'stencil = ##f
  }
}

%% These contexts have reference points at the baseline:
%%   ChordNames, NoteNames, and Lyrics
<<
  \new ChordNames { \chords { g1:m } }
  \new NoteNames { s1 | g1 | }
  \new RhythmicStaff {
    \set RhythmicStaff.instrumentName = #"baseline "
    \textLengthOn
    \labelContext "ChordNames" s1 |
    \labelContext "NoteNames"  s1 |
    \labelContext "Lyrics"     s1 |
  }
  \new Lyrics { \lyrics { \skip 1*2 | ghijk1 | } }
>>

%% The reference point for Dynamics is its vertical center
<<
  \new RhythmicStaff {
    \set RhythmicStaff.instrumentName = #"vertical center "
    \labelContext "Dynamics" s1*3
  }
  \new Dynamics { s2\mp s\fp }
>>

%% The reference point for FiguredBass is its highest point
<<
  \new RhythmicStaff {
    \set RhythmicStaff.instrumentName = #"highest point "
    \labelContext "FiguredBass" s1
  }
  \new FiguredBass { \figuremode { <6 5>1 } }
>>

%% The reference point for FretBoards is the top line
\include "predefined-guitar-fretboards.ly"
<<
  \new FretBoards { \chordmode { e1 } }
  \new RhythmicStaff {
    \set RhythmicStaff.instrumentName = #"top line "
    \labelContext "FretBoards " s1
  }
>>
@end lilypond

Each of the vertical spacing grob properties (except
@code{staff-affinity}) is stored as an alist (association list),
and each uses the same alist structure as the @code{\paper}
spacing variables discussed in @ref{Flexible vertical dimensions}.
Specific methods for modifying alists are discussed in
@ref{Modifying alists}.  Grob properties should be adjusted with
an @code{\override} inside a @code{\score} or @code{\layout}
block, and not inside a @code{\paper} block.

The following example demonstrates the two ways these alists can
be modified.  The first declaration updates one key-value
individually, and the second completely re-defines the property:

@example
\new Staff \with @{
  \override VerticalAxisGroup #'staff-staff-spacing #'space = #10
@} @{ @dots{} @}

\new Staff \with @{
  \override VerticalAxisGroup #'staff-staff-spacing =
    #'((padding . 1)
       (space . 10)
       (minimum-distance . 9)
       (stretchability . 10))
@} @{ @dots{} @}
@end example

To change any spacing settings globally, put them in the
@code{\layout} block:

@example
\layout @{
  \context @{
    \Staff
    \override VerticalAxisGroup #'staff-staff-spacing #'space = #10
  @}
@}
@end example

Standard settings for the vertical spacing grob properties are
listed in @rinternals{VerticalAxisGroup} and
@rinternals{StaffGrouper}.  Default overrides for specific types
of non-staff lines are listed in the relevant context descriptions
in @rinternals{Contexts}.


@subsubheading Properties of the @code{VerticalAxisGroup} grob

@code{VerticalAxisGroup} properties are typically adjusted with an
@code{\override} at the @code{Staff} level (or equivalent).

@table @code
@item staff-staff-spacing
The distance between the current staff and the staff just below it
in the same system, even if one or more non-staff lines (such as
@code{Lyrics}) are placed between the two staves.  Does not apply
to the bottom staff of a system.  This replaces any settings
inherited from the @code{StaffGrouper} grob of the containing
staff-group, if there is one.  If this is unset, and there are no
@code{StaffGrouper} properties to inherit, the
@code{default-staff-staff-spacing} property is used.

@item default-staff-staff-spacing
The settings to use for @code{staff-staff-spacing} when it is
unset.  This applies to ungrouped staves and to grouped staves
that do not inherit settings from the @code{StaffGrouper} grob.

@item staff-affinity
The direction of the staff to use for spacing the current
non-staff line.  Choices are @code{UP}, @code{DOWN}, and
@code{CENTER}.  If @code{CENTER}, the non-staff line will be
placed equidistant between the two nearest staves on either side,
unless collisions or other spacing constraints prevent this.
Adjacent non-staff lines should have non-increasing
@code{staff-affinity} from top to bottom, e.g. a non-staff line
set to @code{UP} should not immediately follow one that is set to
@code{DOWN}.  Non-staff lines at the top of a system should use
@code{DOWN}; those at the bottom should use @code{UP}.  Setting
@code{staff-affinity} for a staff causes it to be treated as a
non-staff line.  Setting @code{staff-affinity} to @code{#f} causes
a non-staff line to be treated as a staff.

@c TODO: verify last clause below ("even if other...")

@item nonstaff-relatedstaff-spacing
The distance between the current non-staff line and the nearest
staff in the direction of @code{staff-affinity}, if there are no
non-staff lines between the two, and @code{staff-affinity} is
either @code{UP} or @code{DOWN}.  If @code{staff-affinity} is
@code{CENTER}, then @code{nonstaff-relatedstaff-spacing} is used
for the nearest staves on @emph{both} sides, even if other
non-staff lines appear between the current one and either of the
staves.

@item nonstaff-nonstaff-spacing
The distance between the current non-staff line and the next
non-staff line in the direction of @code{staff-affinity}, if both
are on the same side of the related staff, and
@code{staff-affinity} is either @code{UP} or @code{DOWN}.

@item nonstaff-unrelatedstaff-spacing
The distance between the current non-staff line and the staff in
the opposite direction from @code{staff-affinity}, if there are no
other non-staff lines between the two, and @code{staff-affinity}
is either @code{UP} or @code{DOWN}.  This can be used, for
example, to require a minimum amount of padding between a
@code{Lyrics} line and the staff to which it does not belong.
@end table


@subsubheading Properties of the @code{StaffGrouper} grob

@code{StaffGrouper} properties are typically adjusted with an
@code{\override} at the @code{StaffGroup} level (or equivalent).

@table @code
@item staff-staff-spacing
The distance between consecutive staves within the current
staff-group.  The @code{staff-staff-spacing} property of an
individual staff's @code{VerticalAxisGroup} grob will be used
instead for any staves in the staff-group that have it set.  Also
see @code{default-staff-staff-spacing}.

@item staffgroup-staff-spacing
The distance between the last staff of the current staff-group and
the staff just below it in the same system, even if one or more
non-staff lines (such as @code{Lyrics}) exist between the two
staves.  Does not apply to the bottom staff of a system.  The
@code{staff-staff-spacing} property of an individual staff's
@code{VerticalAxisGroup} grob will be used instead for any staves
in the staff-group that have it set.  Also see
@code{default-staff-staff-spacing}.
@end table

@seealso
Installed files:
@file{ly/engraver-init.ly},
@file{scm/define-grobs.scm}.

Internals Reference:
@rinternals{Contexts},
@rinternals{VerticalAxisGroup},
@rinternals{StaffGrouper}.


@node Spacing of ungrouped staves
@unnumberedsubsubsec Spacing of ungrouped staves

@emph{Staves} (such as @code{Staff}, @code{DrumStaff},
@code{TabStaff}, etc.) are contexts that can contain one or more
voice contexts, but cannot contain any other staves.

The following properties affect the spacing of @emph{ungrouped}
staves:

@itemize
@item @code{VerticalAxisGroup} properties:
@itemize
@item @code{staff-staff-spacing}
@end itemize
@end itemize

These grob properties are described individually above; see
@ref{Within-system spacing properties}.

Additional properties are involved for staves that are part of a
staff-group; see @ref{Spacing of grouped staves}.

The following example shows how the @code{staff-staff-spacing}
property can affect the spacing of ungrouped staves:

@lilypond[verbatim,quote,staffsize=16]
\layout {
  \context {
    \Staff
    \override VerticalAxisGroup #'staff-staff-spacing =
      #'((padding . 1)
         (space . 8)
         (minimum-distance . 7))
  }
}

\new StaffGroup <<
  % The very low note here needs more room than 'space can
  % provide, so the distance between this staff and the next is
  % determined by 'padding.
  \new Staff { b,2 r | }

  % Here, 'space provides enough room, and there is no need to
  % compress the space (towards 'minimum-distance) to make room
  % for anything else on the page, so the distance between this
  % staff and the next is determined by 'space.
  \new Staff { \clef bass g2 r | }

  % By setting 'padding to a negative value, staves can be made to
  % collide.  The lowest acceptable value for 'space is 0.
  \new Staff \with {
    \override VerticalAxisGroup #'staff-staff-spacing =
      #'((padding . -10)
         (space . 3.5))
  } { \clef bass g2 r | }
  \new Staff { \clef bass g2 r | }
>>
@end lilypond

@seealso
Installed Files:
@file{scm/define-grobs.scm}.

Snippets:
@rlsr{Spacing}.

Internals Reference:
@rinternals{VerticalAxisGroup}.


@node Spacing of grouped staves
@unnumberedsubsubsec Spacing of grouped staves

In orchestral and other large scores, it is common to place staves
in groups.  The space between groups is typically larger than the
space between staves of the same group.

@emph{Staff-groups} (such as @code{StaffGroup}, @code{ChoirStaff},
etc.) are contexts that can contain one or more staves
simultaneously.

The following properties affect the spacing of staves inside
staff-groups:

@itemize
@item @code{VerticalAxisGroup} properties:
@itemize
@item @code{staff-staff-spacing}
@item @code{default-staff-staff-spacing}
@end itemize
@item @code{StaffGrouper} properties:
@itemize
@item @code{staff-staff-spacing}
@item @code{staffgroup-staff-spacing}
@end itemize
@end itemize

These grob properties are described individually above; see
@ref{Within-system spacing properties}.

The following example shows how properties of the
@code{StaffGrouper} grob can affect the spacing of grouped staves:

@lilypond[verbatim,quote,staffsize=16]
\layout {
  \context {
    \Score
    \override StaffGrouper #'staff-staff-spacing #'padding = #0
    \override StaffGrouper #'staff-staff-spacing #'space = #1
  }
}

<<
  \new PianoStaff \with {
    \override StaffGrouper #'staffgroup-staff-spacing #'space = #20
  } <<
    \new Staff { c'1 }
    \new Staff { c'1 }
  >>

  \new StaffGroup <<
    \new Staff { c'1 }
    \new Staff { c'1 }
  >>
>>
@end lilypond

@seealso
Installed Files:
@file{scm/define-grobs.scm}.

Snippets:
@rlsr{Spacing}.

Internals Reference:
@rinternals{VerticalAxisGroup},
@rinternals{StaffGrouper}.


@node Spacing of non-staff lines
@unnumberedsubsubsec Spacing of non-staff lines

@emph{Non-staff lines} (such as @code{Lyrics}, @code{ChordNames},
etc.) are contexts whose layout objects are engraved like staves
(i.e. in horizontal lines within systems).  Specifically,
non-staff lines are non-staff contexts that create the
@code{VerticalAxisGroup} layout object.

The following properties affect the spacing of non-staff lines:

@itemize
@item @code{VerticalAxisGroup} properties:
@itemize
@item @code{staff-affinity}
@item @code{nonstaff-relatedstaff-spacing}
@item @code{nonstaff-nonstaff-spacing}
@item @code{nonstaff-unrelatedstaff-spacing}
@end itemize
@end itemize

These grob properties are described individually above; see
@ref{Within-system spacing properties}.

The following example shows how the
@code{nonstaff-nonstaff-spacing} property can affect the spacing
of consecutive non-staff lines.  Here, by setting the
@code{stretchability} key to a very high value, the lyrics are
able to stretch much more than usual:

@lilypond[verbatim,quote,staffsize=16]
\layout {
  \context {
    \Lyrics
    \override VerticalAxisGroup
      #'nonstaff-nonstaff-spacing #'stretchability = #1000
  }
}

\new StaffGroup
<<
  \new Staff \with {
    \override VerticalAxisGroup #'staff-staff-spacing = #'((space . 30))
  } { c'1 }
  \new Lyrics \with {
    \override VerticalAxisGroup #'staff-affinity = #UP
  } \lyricmode { up }
  \new Lyrics \with {
    \override VerticalAxisGroup #'staff-affinity = #CENTER
  } \lyricmode { center }
  \new Lyrics \with {
    \override VerticalAxisGroup #'staff-affinity = #DOWN
  } \lyricmode { down }
  \new Staff { c'1 }
>>
@end lilypond


@seealso
Installed Files:
@file{ly/engraver-init.ly},
@file{scm/define-grobs.scm}.

Snippets:
@rlsr{Spacing}.

@c @lsr{spacing,page-spacing.ly},
@c @lsr{spacing,alignment-vertical-spacing.ly}.

Internals Reference:
@rinternals{Contexts},
@rinternals{VerticalAxisGroup}.


@node Explicit staff and system positioning
@subsection Explicit staff and system positioning

One way to understand the @code{VerticalAxisGroup} and @code{\paper}
settings explained in the previous two sections is as a collection of
different settings that primarily concern the amount of vertical padding
different staves and systems running down the page.

It is possible to approach vertical spacing in a different way using
@code{NonMusicalPaperColumn #'line-break-system-details}.  Where
@code{VerticalAxisGroup} and @code{\paper} settings specify vertical padding,
@code{NonMusicalPaperColumn #'line-break-system-details} specifies exact
vertical positions on the page.

@code{NonMusicalPaperColumn #'line-break-system-details} accepts an associative
list of three different settings:

@itemize
@item @code{X-offset}
@item @code{Y-offset}
@item @code{alignment-distances}
@end itemize

Grob overrides, including the overrides for @code{NonMusicalPaperColumn}
below, can occur in any of three different places in an input file:

@itemize
@item in the middle of note entry directly
@item in a @code{\context} block
@item in the @code{\with} block
@end itemize

When we override @code{NonMusicalPaperColumn}, we use the usual
@code{\override} command in @code{\context} blocks and in the
@code{\with} block.  On the other hand, when we override
@code{NonMusicalPaperColumn} in the middle of note entry,
use the special @code{\overrideProperty} command.  Here are some
example @code{NonMusicalPaperColumn} overrides with the special
@code{\overrideProperty} command:

@example
\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((X-offset . 20))

\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((Y-offset . 40))

\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((X-offset . 20) (Y-offset . 40))

\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((alignment-distances . (15)))

\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((X-offset . 20) (Y-offset . 40)
                                 (alignment-distances . (15)))
@end example

To understand how each of these different settings work, we begin
by looking at an example that includes no overrides at all.

@c \book { } is required in these examples to ensure the spacing
@c overrides can be seen between systems. -np

@lilypond[quote]
\header { tagline = ##f }
\paper { left-margin = 0\mm }
\book {
  \score {
    <<
      \new Staff <<
        \new Voice {
          s1*5 \break
          s1*5 \break
          s1*5 \break
        }
        \new Voice { \repeat unfold 15 { c'4 c' c' c' } }
      >>
      \new Staff {
        \repeat unfold 15 { d'4 d' d' d' }
      }
    >>
  }
}
@end lilypond

This score isolates line- and page-breaking information in a dedicated
voice.  This technique of creating a breaks voice will help keep layout
separate from music entry as our example becomes more complicated.
See @ref{Using an extra voice for breaks}.

Explicit @code{\breaks} evenly divide the music into six measures per
line.  Vertical spacing results from LilyPond's defaults.  To set
the vertical startpoint of each system explicitly, we can set
the @code{Y-offset} pair in the @code{line-break-system-details}
attribute of the @code{NonMusicalPaperColumn} grob:

@lilypond[quote]
\header { tagline = ##f }
\paper { left-margin = 0\mm }
\book {
  \score {
    <<
      \new Staff <<
        \new Voice {
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 0))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 40))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 80))
          s1*5 \break
        }
        \new Voice { \repeat unfold 15 { c'4 c' c' c' } }
      >>
      \new Staff {
        \repeat unfold 15 { d'4 d' d' d' }
      }
    >>
  }
}
@end lilypond

Note that @code{line-break-system-details} takes an associative list of
potentially many values, but that we set only one value here.  Note,
too, that the @code{Y-offset} property here determines the exact vertical
position on the page at which each new system will render.

Now that we have set the vertical startpoint of each system
explicitly, we can also set the vertical distances between staves
within each system manually.  We do this using the @code{alignment-distances}
subproperty of @code{line-break-system-details}.

@lilypond[quote]
\header { tagline = ##f }
\paper { left-margin = 0\mm }
\book {
  \score {
    <<
      \new Staff <<
        \new Voice {
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 20)
                                           (alignment-distances . (15)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 60)
                                           (alignment-distances . (15)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 100)
                                           (alignment-distances . (15)))
          s1*5 \break
        }
        \new Voice { \repeat unfold 15 { c'4 c' c' c' } }
      >>
      \new Staff {
        \repeat unfold 15 { d'4 d' d' d' }
      }
    >>
  }
}
@end lilypond

Note that here we assign two different values to the
@code{line-break-system-details} attribute of the
@code{NonMusicalPaperColumn} grob.  Though the
@code{line-break-system-details} attribute alist accepts many
additional spacing parameters (including, for example, a corresponding
@code{X-offset} pair), we need only set the @code{Y-offset} and
@code{alignment-distances} pairs to control the vertical startpoint of
every system and every staff.  Finally, note that @code{alignment-distances}
specifies the vertical positioning of staves but not of staff groups.

@lilypond[quote]
\header { tagline = ##f }
\paper { left-margin = 0\mm }
\book {
  \score {
    <<
      \new Staff <<
        \new Voice {
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 0)
                                           (alignment-distances . (30 10)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 60)
                                           (alignment-distances . (10 10)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 100)
                                           (alignment-distances . (10 30)))
          s1*5 \break
        }
        \new Voice { \repeat unfold 15 { c'4 c' c' c' } }
      >>
      \new StaffGroup <<
        \new Staff { \repeat unfold 15 { d'4 d' d' d' } }
        \new Staff { \repeat unfold 15 { e'4 e' e' e' } }
      >>
    >>
  }
}
@end lilypond

Some points to consider:

@itemize
@item When using @code{alignment-distances}, lyrics and other non-staff lines
do not count as a staff.

@item The units of the numbers passed to @code{X-offset},
@code{Y-offset} and @code{alignment-distances} are interpreted as multiples
of the distance between adjacent staff lines.  Positive values move staves
and lyrics up, negative values move staves and lyrics down.

@item Because the @code{NonMusicalPaperColumn #'line-break-system-details}
settings given here allow the positioning of staves and systems anywhere
on the page, it is possible to violate paper or margin boundaries or even
to print staves or systems on top of one another.  Reasonable values
passed to these different settings will avoid this.
@end itemize


@seealso
Snippets:
@rlsr{Spacing}.


@node Vertical collision avoidance
@subsection Vertical collision avoidance

@funindex outside-staff-priority
@funindex outside-staff-padding
@funindex outside-staff-horizontal-padding

Intuitively, there are some objects in musical notation that belong
to the staff and there are other objects that should be placed outside
the staff.  Objects belonging outside the staff include things such as
rehearsal marks, text and dynamic markings (from now on, these will
be called outside-staff objects).  LilyPond's rule for the
vertical placement of outside-staff objects is to place them as close
to the staff as possible but not so close that they collide with
another object.

LilyPond uses the @code{outside-staff-priority} property to determine
whether a grob is an outside-staff object: if @code{outside-staff-priority}
is a number, the grob is an outside-staff object.  In addition,
@code{outside-staff-priority} tells LilyPond in which order the objects
should be placed.

First, LilyPond places all the objects that do not belong outside
the staff.  Then it sorts the outside-staff objects according to their
@code{outside-staff-priority} (in increasing order).  One by one, LilyPond
takes the outside-staff objects and places them so that they do
not collide with any objects that have already been placed.  That
is, if two outside-staff grobs are competing for the same space, the one
with the lower @code{outside-staff-priority} will be placed closer to
the staff.

@lilypond[quote,ragged-right,relative=2,verbatim]
c4_"Text"\pp
r2.
\once \override TextScript #'outside-staff-priority = #1
c4_"Text"\pp % this time the text will be closer to the staff
r2.
% by setting outside-staff-priority to a non-number,
% we disable the automatic collision avoidance
\once \override TextScript #'outside-staff-priority = ##f
\once \override DynamicLineSpanner #'outside-staff-priority = ##f
c4_"Text"\pp % now they will collide
@end lilypond

The vertical padding between an outside-staff object and the
previously-positioned grobs can be controlled with
@code{outside-staff-padding}.

@lilypond[quote,ragged-right,relative=2,verbatim]
\once \override TextScript #'outside-staff-padding = #0
a'^"This text is placed very close to the note"
\once \override TextScript #'outside-staff-padding = #3
c^"This text is padded away from the previous text"
c^"This text is placed close to the previous text"
@end lilypond


By default, outside-staff objects are placed only to avoid
a horizontal collision with previously-positioned grobs.  This
can lead to situations in which objects are placed very close to each
other horizontally.  The vertical spacing between staves can
also be set so that outside staff objects are interleaved.
Setting @code{outside-staff-horizontal-padding}
causes an object to be offset vertically so that such a situation
doesn't occur.

@lilypond[quote,ragged-right,relative=2,verbatim]
% the markup is too close to the following note
c4^"Text"
c4
c''2
% setting outside-staff-horizontal-padding fixes this
R1
\once \override TextScript #'outside-staff-horizontal-padding = #1
c,,4^"Text"
c4
c''2
@end lilypond


@seealso
Snippets:
@rlsr{Spacing}.


@node Horizontal spacing
@section Horizontal spacing

@cindex horizontal spacing
@cindex spacing, horizontal

@menu
* Horizontal spacing overview::
* New spacing area::
* Changing horizontal spacing::
* Line length::
* Proportional notation::
@end menu


@node Horizontal spacing overview
@subsection Horizontal spacing overview

The spacing engine translates differences in durations into stretchable
distances (@q{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 @rinternals{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[quote,verbatim,relative=1]
c2 c4. c8 c4. c8 c4. c8 c8
c8 c4 c4 c4
@end lilypond

Normally, @code{spacing-increment} is set to 1.2 staff space, which is
approximately the width of a note head, and
@code{shortest-duration-space} is set to 2.0, meaning that the
shortest note gets 2.4 staff space (2.0 times the
@code{spacing-increment}) of horizontal space.  This space is 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
32nd 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 rather
the one which occurs most frequently.


The most common shortest duration is determined as follows: in every
measure, the shortest duration is determined.  The most common shortest
duration is taken as the basis for the spacing, with the stipulation
that this shortest duration should always be equal to or shorter than
an 8th note.  The shortest duration is printed when you run
@code{lilypond} with the @code{--verbose} option.

These durations may also be customized.  If you set the
@code{common-shortest-duration} in @rinternals{SpacingSpanner}, then
this sets the base duration for spacing.  The maximum duration for this
base (normally an 8th), is set through @code{base-shortest-duration}.

@funindex common-shortest-duration
@funindex base-shortest-duration
@funindex stem-spacing-correction
@funindex spacing

Notes that are even shorter than the common shortest note 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[quote,verbatim,relative=2]
c2 c4. c8 c4. c16[ c] c4. c8 c8 c8 c4 c4 c4
@end lilypond


In the @emph{Essay on automated music engraving}, it was explained
that stem directions influence spacing (see @ressay{Optical
spacing}).  This is controlled with the
@code{stem-spacing-correction} property in the
@rinternals{NoteSpacing}, object.  These are generated for every
@rinternals{Voice} context.  The @code{StaffSpacing} object
(generated in @rinternals{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[quote,ragged-right]
{
  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 |
}
@end lilypond

Proportional notation is supported; see @ref{Proportional notation}.


@seealso
Snippets:
@rlsr{Spacing}.

Internals Reference:
@rinternals{SpacingSpanner},
@rinternals{NoteSpacing},
@rinternals{StaffSpacing},
@rinternals{NonMusicalPaperColumn}.


@knownissues

There is no convenient mechanism to manually override spacing.  The
following work-around may be used to insert extra space into a score,
adjusting the padding value as necessary.
@example
 \override Score.NonMusicalPaperColumn #'padding = #10
@end example

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


@node New spacing area
@subsection New spacing area

New sections with different spacing parameters can be started with
@code{newSpacingSection}.  This is useful when there are
sections with a different notions of long and short notes.

In the following example, the time signature change introduces a new
section, and hence the 16ths notes are spaced wider.

@lilypond[relative=1,verbatim,quote]
\time 2/4
c4 c8 c
c8 c c4 c16[ c c8] c4
\newSpacingSection
\time 4/16
c16[ c c8]
@end lilypond

The @code{\newSpacingSection} command creates a new
@code{SpacingSpanner} object, and hence new @code{\override}s
may be used in that location.


@seealso
Snippets:
@rlsr{Spacing}.

Internals Reference:
@rinternals{SpacingSpanner}.


@node Changing horizontal spacing
@subsection Changing horizontal spacing

Horizontal spacing may be altered with the
@code{base-shortest-duration} property.  Here
we compare the same music; once without altering
the property, and then altered.  Larger values
of @code{ly:make-moment} will produce smaller
music.  Note that @code{ly:make-moment} constructs
a duration, so @code{1 4} is a longer duration
than @code{1 16}.

@lilypond[verbatim,line-width=12\cm]
\score {
  \relative c'' {
    g4 e e2 | f4 d d2 | c4 d e f | g4 g g2 |
    g4 e e2 | f4 d d2 | c4 e g g | c,1 |
    d4 d d d | d4 e f2 | e4 e e e | e4 f g2 |
    g4 e e2 | f4 d d2 | c4 e g g | c,1 |
  }
}
@end lilypond

@lilypond[verbatim,line-width=12\cm]
\score {
  \relative c'' {
    g4 e e2 | f4 d d2 | c4 d e f | g4 g g2 |
    g4 e e2 | f4 d d2 | c4 e g g | c,1 |
    d4 d d d | d4 e f2 | e4 e e e | e4 f g2 |
    g4 e e2 | f4 d d2 | c4 e g g | c,1 |
  }
  \layout {
    \context {
      \Score
      \override SpacingSpanner
        #'base-shortest-duration = #(ly:make-moment 1 16)
    }
  }
}
@end lilypond


@snippets

By default, spacing in tuplets depends on various non-duration
factors (such as accidentals, clef changes, etc).  To disregard
such symbols and force uniform equal-duration spacing, use
@code{Score.SpacingSpanner #'uniform-stretching}.  This
property can only be changed at the beginning of a score,

@lilypond[quote,ragged-right,verbatim]
\score {
  <<
    \new Staff {
      \times 4/5 {
        c8 c8 c8 c8 c8
      }
      c8 c8 c8 c8
    }
    \new Staff {
      c8 c8 c8 c8
      \times 4/5 {
        c8 c8 c8 c8 c8
      }
    }
  >>
  \layout {
    \context {
      \Score
      \override SpacingSpanner #'uniform-stretching = ##t
    }
  }
}
@end lilypond

When @code{strict-note-spacing} is set, notes are spaced without
regard for clefs, bar lines, and grace notes,

@lilypond[quote,ragged-right,relative=2,verbatim]
\override Score.SpacingSpanner #'strict-note-spacing = ##t
\new Staff { c8[ c \clef alto c \grace { c16[ c] } c8 c c]  c32[ c32] }
@end lilypond


@seealso
Snippets:
@rlsr{Spacing}.


@node Line length
@subsection Line length

@cindex page breaks
@cindex breaking pages

@funindex indent
@funindex line-width
@funindex ragged-right
@funindex ragged-last

@c Although line-width can be set in \layout, it should be set in paper
@c block, to get page layout right.
@c Setting indent in \paper block makes not much sense, but it works.

@c Bit verbose and vague, use examples?
The most basic settings influencing the spacing are @code{indent} and
@code{line-width}.  They are set in the @code{\layout} block.  They
control the indentation of the first line of music, and the lengths of
the lines.

If @code{ragged-right} is set to true in the @code{\layout} block, then
systems ends at their natural horizontal length, instead of being spread
horizontally to fill the whole line.  This is useful for
short fragments, and for checking how tight the natural spacing is.
The normal default setting is false, but if the score has only one
system the default value is true.

@cindex page layout
@cindex vertical spacing

The option @code{ragged-last} is similar to @code{ragged-right}, but
only affects the last line of the piece.  No restrictions are put on
that line.  The result is similar to formatting text paragraphs.  In a
paragraph, the last line simply takes its natural horizontal length.
@c Note that for text there are several options for the last line.
@c While Knuth TeX uses natural length, lead typesetters use the same
@c stretch as the previous line.  eTeX uses \lastlinefit to
@c interpolate between both these solutions.

@example
\layout @{
  indent = #0
  line-width = #150
  ragged-last = ##t
@}
@end example


@seealso
Snippets:
@rlsr{Spacing}.


@node Proportional notation
@subsection Proportional notation

LilyPond supports proportional notation, a type of horizontal spacing
in which each note consumes an amount of horizontal space exactly
equivalent to its rhythmic duration.  This type of proportional spacing
is comparable to horizontal spacing on top of graph paper.  Some late
20th- and early 21st-century scores use proportional notation to
clarify complex rhythmic relationships or to facilitate the placement
of timelines or other graphics directly in the score.

LilyPond supports five different settings for proportional notation,
which may be used together or alone:

@itemize
@item @code{proportionalNotationDuration}
@item @code{uniform-stretching}
@item @code{strict-note-spacing}
@item @code{\remove Separating_line_group_engraver}
@item @code{\override PaperColumn #'used = ##t}
@end itemize

In the examples that follow, we explore these five different
proportional notation settings and examine how these settings interact.

We start with the following one-measure example, which uses classical
spacing with ragged-right turned on.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
  >>
}
@end lilypond

Notice that the half note which begins the measure takes up far less
than half of the horizontal space of the measure.  Likewise, the
sixteenth notes and sixteenth-note quintuplets (or twentieth notes)
which end the measure together take up far more than half the
horizontal space of the measure.

In classical engraving, this spacing may be exactly what we want
because we can borrow horizontal space from the half note and conserve
horizontal space across the measure as a whole.

On the other hand, if we want to insert a measured timeline or other
graphic above or below our score, we need proportional notation.  We
turn proportional notation on with the proportionalNotationDuration
setting.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
  >>
 \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 20)
    }
  }
}
@end lilypond

The half note at the beginning of the measure and the faster notes in
the second half of the measure now occupy equal amounts of horizontal
space.  We could place a measured timeline or graphic above or below
this example.

The @code{proportionalNotationDuration} setting is a context setting
that lives in @code{Score}.  Remember that context settings can appear
in one of three locations within our input file -- in a @code{\with}
block, in a @code{\context} block, or directly in music entry preceded
by the @code{\set} command.  As with all context settings, users can
pick which of the three different locations they would like to
set @code{proportionalNotationDuration} in to.

The @code{proportionalNotationDuration} setting takes a single argument,
which is the reference duration against that all music will be spaced.
The LilyPond Scheme function @code{make-moment} takes two arguments
-- a numerator and denominator which together express some fraction of
a whole note.  The call @code{#(ly:make-moment 1 20)} therefore produces
a reference duration of a twentieth note.  Values such as
@code{#(ly:make-moment 1 16)}, @code{#(ly:make-moment 1 8)}, and
@code{#(ly:make-moment 3 97)} are all possible as well.

How do we select the right reference duration to pass to
@code{proportionalNotationDuration}?  Usually by a process of trial
and error, beginning with a duration close to the fastest (or smallest)
duration in the piece.  Smaller reference durations space music loosely;
larger reference durations space music tightly.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
  >>
  \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 8)
    }
  }
}

\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
  >>
  \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 16)
    }
  }
}

\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
  >>
  \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 32)
    }
  }
}
@end lilypond

Note that too large a reference duration -- such as the eighth note,
above -- spaces music too tightly and can cause note head collisions.
Also that proportional notation in general takes up more horizontal
space than classical spacing.  Proportional spacing provides rhythmic
clarity at the expense of horizontal space.

Next we examine how to optimally space overlapping tuplets.

We start by examining what happens to our original example, with
classical spacing, when we add a second staff with a different type of
tuplet.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
    \new RhythmicStaff {
      \times 8/9 {
        c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8
      }
    }
  >>
}
@end lilypond

The spacing is bad because the evenly spaced notes of the bottom staff
do not stretch uniformly.  Classical engravings include very few complex
triplets and so classical engraving rules can generate this type of
result.  Setting @code{proportionalNotationDuration} fixes this.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
    \new RhythmicStaff {
      \times 8/9 {
        c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8
      }
    }
  >>
  \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 20)
    }
  }
}
@end lilypond

But if we look very carefully we can see that notes of the second half
of the 9-tuplet space ever so slightly more widely than the notes
of the first half of the 9-tuplet.  To ensure uniform stretching, we
turn on @code{uniform-stretching}, which is a property of
@code{SpacingSpanner}.

@lilypond[quote,verbatim,ragged-right]
\score {
  <<
    \new RhythmicStaff {
      c'2
      c'16 c'16 c'16 c'16
      \times 4/5 {
        c'16 c'16 c'16 c'16 c'16
      }
    }
    \new RhythmicStaff {
      \times 8/9 {
        c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8 c'8
      }
    }
  >>
  \layout {
    \context {
      \Score
      proportionalNotationDuration = #(ly:make-moment 1 20)
      \override SpacingSpanner #'uniform-stretching = ##t
    }
  }
}
@end lilypond

Our two-staff example now spaces exactly, our rhythmic
relationships are visually clear, and we can include a measured
timeline or graphic if we want.

Note that the LilyPond's proportional notation package expects
that all proportional scores set the SpacingSpanner's
'uniform-stretching attribute to ##t.  Setting
proportionalNotationDuration without also setting the
SpacingSpanner's 'uniform-stretching attribute to ##t will, for
example, cause Skips to consume an incorrect amount of horizontal
space.

The SpacingSpanner is an abstract grob that lives in the Score
context.  As with our settings of proportionalNotationDuration,
overrides to the SpacingSpanner can occur in any of three
different places in our input file – in the Score \with block, in
a Score \context block, or in note entry directly.

There is by default only one @code{SpacingSpanner} per @code{Score}.  This
means that, by default, @code{uniform-stretching} is either turned on for the
entire score or turned off for the entire score.  We can, however,
override this behavior and turn on different spacing features at
different places in the score.  We do this with the command
@code{\newSpacingSection}.  See @ref{New spacing area}, for more info.

Next we examine the effects of the @code{Separating_line_group_engraver} and
see why proportional scores frequently remove this engraver.  The following
example shows that there is a small amount of @qq{preferatory} space
just before the first note in each system.

@lilypond[quote,verbatim,ragged-right]
\paper {
  indent = #0
}

\new Staff {
  c'1
  \break
  c'1
}
@end lilypond


The amount of this preferatory space is the same whether after a time
signature, a key signature or a clef.  @code{Separating_line_group_engraver}
is responsible for this space.  Removing @code{Separating_line_group_engraver}
reduces this space to zero.

@lilypond[quote,verbatim,ragged-right]
\paper {
  indent = #0
}

\new Staff \with {
  \remove Separating_line_group_engraver
} {
  c'1
  \break
  c'1
}
@end lilypond

Nonmusical elements like time signatures, key signatures, clefs and
accidentals are problematic in proportional notation.  None of these
elements has rhythmic duration.  But all of these elements consume
horizontal space.  Different proportional scores approach these
problems differently.

It may be possible to avoid spacing problems with key signatures
simply by not having any.  This is a valid option since most
proportional scores are contemporary music.  The same may be true
of time signatures, especially for those scores
that include a measured timeline or other graphic.  But these scores
are exceptional and most proportional scores include at least some
time signatures.  Clefs and accidentals are even more essential.

So what strategies exist for spacing nonmusical elements in a
proportional context?  One good option is the @code{strict-note-spacing}
property of @code{SpacingSpanner}.  Compare the two scores below:

@lilypond[quote,verbatim,ragged-right]
\new Staff {
  \set Score.proportionalNotationDuration = #(ly:make-moment 1 16)
  c''8
  c''8
  c''8
  \clef alto
  d'8
  d'2
}

\new Staff {
  \set Score.proportionalNotationDuration = #(ly:make-moment 1 16)
  \override Score.SpacingSpanner #'strict-note-spacing = ##t
  c''8
  c''8
  c''8
  \clef alto
  d'8
  d'2
}
@end lilypond

Both scores are proportional, but the spacing in the first score
is too loose because of the clef change.  The spacing of the second
score remains strict, however, because strict-note-spacing is
turned on.  Turning on strict-note-spacing causes the width of
time signatures, key signatures, clefs and accidentals to play no
part in the spacing algorithm.

In addition to the settings given here, there are other settings
that frequently appear in proportional scores.  These include:

@itemize
@item @code{\override SpacingSpanner #'strict-grace-spacing = ##t}
@item @code{tupletFullLength = ##t}
@item @code{\override Beam #'breakable = ##t}
@item @code{\override Glissando #'breakable = ##t}
@item @code{\override TextSpanner #'breakable = ##t}
@item @code{\remove Forbid_line_break_engraver in the Voice context}
@end itemize

These settings space grace notes strictly, extend tuplet brackets to
mark both rhythmic start- and stop-points, and allow spanning elements
to break across systems and pages.  See the respective parts of the manual
for these related settings.


@seealso
Notation Reference:
@ref{New spacing area}.

Snippets:
@rlsr{Spacing}.


@node Fitting music onto fewer pages
@section Fitting music onto fewer pages

Sometimes you can end up with one or two staves on a second
(or third, or fourth...) page.  This is annoying, especially
if you look at previous pages and it looks like there is plenty
of room left on those.

When investigating layout issues, @code{annotate-spacing} is an
invaluable tool.  This command prints the values of various layout
spacing variables; for more details see the following section,
@ref{Displaying spacing}.

@menu
* Displaying spacing::
* Changing spacing::
@end menu


@node Displaying spacing
@subsection Displaying spacing

@funindex annotate-spacing
@cindex spacing, display of layout

To graphically display the dimensions of vertical layout variables
that may be altered for page formatting, set
@code{annotate-spacing} in the @code{\paper} block:

@c need to have \book{} otherwise we get the separate systems. -hwn
@lilypond[verbatim,quote]
#(set-default-paper-size "a6" 'landscape)
\book {
  \score { { c4 } }
  \paper { annotate-spacing = ##t }
}
@end lilypond


@noindent
All layout dimensions are displayed in staff-spaces, regardless
of the units specified in the @code{\paper} or @code{\layout} block.
In the above example, @code{paper-height} has a value of 59.75
@code{staff-spaces}, and the @code{staff-size} is 20 points (the
default value).  Note that:

@multitable {1 staff-space} {staff-size)/4 * (25.4/72.27) mm}

@item 1 point
@tab = (25.4/72.27) mm

@item 1 staff-space
@tab = (@code{staff-size})/4 pts
@item
@tab = (@code{staff-size})/4 * (25.4/72.27) mm

@end multitable

@noindent
In this case, one @code{staff-space} is approximately equal to
1.757mm.  Thus the @code{paper-height} measurement of 59.75
@code{staff-spaces} is equivalent to 105 millimeters, the height
of @code{a6} paper in landscape orientation.  The pairs
(@var{a},@var{b}) are intervals, where @var{a} is the lower
edge and @var{b} the upper edge of the interval.


@seealso
Notation Reference:
@ref{Setting the staff size}.

Snippets:
@rlsr{Spacing}.


@node Changing spacing
@subsection Changing spacing

The output of @code{annotate-spacing} reveals vertical dimensions
in great detail.  For details about modifying margins and other
layout variables, see @ref{Page formatting}.

Other than margins, there are a few other options to save space:

@itemize
@item
Force systems to move as close together as possible (to fit as
many systems as possible onto a page) while being spaced so that
there is no blank space at the bottom of the page.

@example
\paper @{
  system-system-spacing = #'((padding . 0) (space . 0.1))
  ragged-last-bottom = ##f
  ragged-bottom = ##f
@}
@end example

@item
Force the number of systems.  This can help in two ways.  Just
setting a value, even the same value as the number of systems
being typeset by default, will sometimes cause more systems to
be fitted onto each page, as an estimation step is then bypassed,
giving a more accurate fit to each page.  Also, forcing an actual
reduction in the number of systems may save a further page.  For
example, if the default layout has 11 systems, the following
assignment will force a layout with 10 systems.

@example
\paper @{
  system-count = #10
@}
@end example

@item
Avoid (or reduce) objects that increase the vertical size of a
system.  For example, volta repeats (or alternate repeats) require
extra space.  If these repeats are spread over two systems, they
will take up more space than one system with the volta repeats and
another system without.  For example, dynamics that @q{stick out} of
a system can be moved closer to the staff:

@lilypond[verbatim,quote,relative=1]
e4 c g\f c
e4 c g-\tweak #'X-offset #-2.7 -\tweak #'Y-offset #2.5 \f c
@end lilypond

@item
Alter the horizontal spacing via @code{SpacingSpanner}.  For more
details, see @ref{Changing horizontal spacing}.  The following
example illustrates the default spacing:

@lilypond[verbatim,quote]
\score {
  \relative c'' {
    g4 e e2 |
    f4 d d2 |
    c4 d e f |
    g4 g g2 |
    g4 e e2 |
  }
}
@end lilypond

@noindent
The next example modifies @code{common-shortest-duration} from a
value of @code{1/4} to @code{1/2}.  The quarter note is the most
common and shortest duration in this example, so by making this
duration longer, a @q{squeezing} effect occurs:

@lilypond[verbatim,quote]
\score {
  \relative c'' {
    g4 e e2 |
    f4 d d2 |
    c4 d e f |
    g4 g g2 |
    g4 e e2 |
  }
  \layout {
    \context {
      \Score
      \override SpacingSpanner
        #'common-shortest-duration = #(ly:make-moment 1 2)
    }
  }
}
@end lilypond

@noindent
The @code{common-shortest-duration} property cannot be modified
dynamically, so it must always be placed in a @code{\context}
block so that it applies to the whole score.

@end itemize


@seealso
Notation Reference:
@ref{Page formatting},
@ref{Changing horizontal spacing}.

Snippets:
@rlsr{Spacing}.