Remove two-pass spacing code and documentation.

[lilypond/mpolesky.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.  See TRANSLATION for details.
@end ignore

@c \version "2.12.0"

@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 uncomplete
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

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

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

@menu
* Vertical dimensions::
* Horizontal dimensions::
* Other layout variables::
@end menu


@node Vertical dimensions
@unnumberedsubsubsec Vertical dimensions

These variables are used to set different vertical dimensions on a
page:

@funindex \paper

@table @code

@item after-title-spacing
@funindex after-title-spacing

Specifies how to calculate the space between a title (or top-level markup)
and the system that follows it.  This is an associative list with five
components:
@itemize @bullet
@item @var{space} -- the amount of stretchable space between the baseline
of a title and the center of the staff that follows it;
@item @var{padding} -- the minimum amount of whitespace that must be
present between a title and the staff that follows it;
@item @var{stretchability} -- the ease with which the stretchable
space increases when a page is stretched.
If this is zero, the distance to the next staff will not stretch at all;
@item @var{minimum-distance} -- the minimum distance to place between
the baseline of a title and the center of the staff that follows it. This differs
from @var{padding} in that the height of a staff has no effect on
the application of @var{minimum-distance} (whereas the height of a
staff is crucial for @var{padding}).
@end itemize

If a page has a ragged bottom, @var{space} is not stretched. In particular, the
resulting distance on such a page is the largest of
@itemize @bullet
@item @var{space},
@item @var{minimum-distance}, and
@item @var{padding} plus the smallest distance necessary to eliminate overlap.
@end itemize

@item before-title-spacing
@funindex before-title-spacing

Specifies the spacing between a system and the title (or top-level markup) that
follows it.
The distances are measured from the center of the last staff in the system to
the baseline of the title that follows it.  See @var{after-title-spacing}.

@item between-scores-system-spacing
@funindex between-scores-system-spacing

Specifies the spacing between two systems if they are in different scores, but
there is no title between them. See @var{after-title-spacing}.

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

Specifies the spacing between the center of the bottom staff of one system
and the center of the top staff of the following system.  See @var{after-title-spacing}.

@item between-title-spacing
@funindex between-title-spacing

Specifies the spacing between two titles (or top-level markups).
The distances are measured from the baseline of the first title to the baseline
of the second.  See @var{after-title-spacing}.

@item bottom-margin
@funindex bottom-margin

The margin between footer and bottom of the page.  Default:
@code{6\mm}.

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

Specifies the spacing from the center of the last staff (or the
baseline of the last top-level markup) to the bottom of the
printable area (ie. the top of the bottom margin).
See @var{after-title-spacing}.

@item foot-separation
@funindex foot-separation

Distance between the bottom-most music system and the page
footer.  Default: @code{4\mm}.

@item top-title-spacing
@funindex top-title-spacing

Specifies the spacing from the top of the printable area (ie.
the bottom of the top margin) to the baseline of the title.
See @var{after-title-spacing}.

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

Specifies the spacing from the top of the printable area (ie.
the bottom of the top margin) to the center of the first staff.
This only takes effect if there is no title at the top of the
page (in which case @var{top-title-spacing} is used instead).
See @var{after-title-spacing}.

@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 header and top of the page.  Default:
@code{5\mm}.

@end table


@snippets

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

The page layout itself is done by two functions in the \paper block,
page-music-height and 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 paper block values in Scheme.  In that case mm, in, pt,
and cm are variables defined in paper-defaults.ly with values in
millimeters.  That is why the value 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

You can also define these 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 must be multiplied in the example

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

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.


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

Snippets:
@rlsr{Spacing}.


@node Horizontal dimensions
@unnumberedsubsubsec Horizontal dimensions

@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.}

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

@table @code

@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{paper-width} divided by @code{14}, as determined by
@code{set-default-paper-size} or @code{set-paper-size}.

@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}, as determined by
@code{set-default-paper-size} or @code{set-paper-size}.

@item line-width
@funindex line-width

The width of music systems.  Default: @code{paper-width} minus
@code{20\mm}, as determined by @code{set-default-paper-size} or
@code{set-paper-size}.

@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 short-indent
@funindex short-indent

The level of indentation for all systems in a score besides the
first system.  Default: @code{0}, as determined by
@code{set-default-paper-size} or @code{set-paper-size}.

@end table


@seealso
Snippets:
@rlsr{Spacing}.


@knownissues

The option @code{right-margin} is defined but doesn't set the
right margin yet.  The value for the right margin has to be
defined by adjusting the values of @code{left-margin} and
@code{line-width}.


@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

FIXME: 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 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
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
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-between-system-padding
@funindex page-breaking-between-system-padding

Tricks the page breaker into thinking that
@code{between-system-padding} is set to something different than
it really is.  For example, if this variable is set to something
substantially larger than @code{between-system-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-limit-inter-system-space
@funindex page-limit-inter-system-space

If set to true, limits space between systems on a page with a lot
of space left.  Default: @code{##f}.  For details, see
@ref{Vertical spacing between systems}.

@item page-limit-inter-system-space-factor
@funindex page-limit-inter-system-space-factor

The factor used by @code{page-limit-inter-system-space}.  Default:
@code{1.4}.  For details, see
@ref{Vertical spacing between systems}.

@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 { 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.

@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 @{ \Staff
    \override VerticalAxisGroup #'minimum-Y-extent = #'(-6 . 6)
  @}
  \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,fragment,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 prefered
     #(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 Score \with {
    \override NonMusicalPaperColumn #'line-break-permission = ##f
    \override NonMusicalPaperColumn #'page-break-permission = ##f
  } {
    \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 }
    }
  }
}
@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
\new 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]
\new 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]
\new 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
* Vertical spacing inside a system::
* Vertical spacing between systems::
* Explicit staff and system positioning::
* Vertical collision avoidance::
@end menu


@node Vertical spacing inside a system
@subsection Vertical spacing inside a system

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

The height of each system is determined automatically.  To prevent
staves from bumping into each other, some minimum distances are set.
By changing these, you can put staves closer together.  This
reduces the amount of space each system requires, and may result
in having more systems per page.

Normally staves are stacked vertically.  To make staves maintain a
distance, their vertical size is padded.  This is done with the
property @code{minimum-Y-extent}.  When applied to a
@rinternals{VerticalAxisGroup}, it controls the size of a horizontal
line, such as a staff or a line of lyrics.  @code{minimum-Y-extent}
takes a pair of numbers, so
if you want to make it smaller than its default @code{#'(-4 . 4)}
then you could set

@example
\override Staff.VerticalAxisGroup #'minimum-Y-extent = #'(-3 . 3)
@end example

@noindent
This sets the vertical size of the current staff to 3 staff spaces on
either side of the center staff line.  The value @code{(-3 . 3)} is
interpreted as an interval, where the center line is the 0, so the
first number is generally negative.  The numbers need not match;
for example, the staff can be made larger at the bottom by setting
it to @code{(-6 . 4)}.

@ignore
FIXME: update this section

After page breaks are determined, the vertical spacing within each
system is reevaluated in order to fill the page more evenly; if a page
has space left over, systems are stretched in order to fill that space.
The amount of stretching can be configured though the @code{max-stretch}
property of the @rinternals{VerticalAlignment} grob. By default,
@code{max-stretch} is set to zero, disabling stretching. To enable
stretching, a sane value for @code{max-stretch}
is @code{ly:align-interface::calc-max-stretch}.

In some situations, you may want to stretch most of a system while
leaving some parts fixed.  For example, if a piano part occurs in the
middle of an orchestral score, you may want to leave the piano staves
close to each other while stretching the rest of the score.  The
@code{keep-fixed-while-stretching} property of
@rinternals{VerticalAxisGroup} can be used to achieve this.  When set
to @code{##t}, this property keeps its staff (or line of lyrics) from
moving relative to the one directly above it.  In the example above,
you would override @code{keep-fixed-while-stretching} to @code{##t} in
the second piano staff:

@lilypond[verbatim]
#(set-default-paper-size "a6")
#(set-global-staff-size 14.0)

\book {
\paper {
  ragged-last-bottom = ##f
}

\new Score \with
{
  \override VerticalAlignment #'max-stretch = #ly:align-interface::calc-max-stretch
}
{
\new GrandStaff
<<
  \new StaffGroup
  <<
    \new Staff {c' d' e' f'}
    \new Staff {c' d' e' f'}
    \new Staff {c' d' e' f'}
  >>

  \new PianoStaff
  <<
    \new Staff {c' d' e' f'}
    \new Staff \with {
      \override VerticalAxisGroup #'keep-fixed-while-stretching = ##t
    }
    {c' d' e' f'}
  >>

  \new StaffGroup
  <<
    \new Staff {c' d' e' f'}
    \new Staff {c' d' e' f'}
  >>
>>
}
}
@end lilypond
@end ignore

Vertical alignment of staves is handled by the
@code{VerticalAlignment} object.  The context parameters
specifying the vertical extent are described in connection with
the @code{Axis_group_engraver}.


@seealso
Snippets:
@rlsr{Spacing}.

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

Internals Reference:
@rinternals{VerticalAlignment},
@rinternals{Axis_group_engraver}.


@node Vertical spacing between systems
@subsection Vertical spacing between systems

Space between systems are controlled by four @code{\paper} variables,

@example
\paper @{
  between-system-space = 1.5\cm
  between-system-padding = #1
  ragged-bottom=##f
  ragged-last-bottom=##f
@}
@end example

When only a couple of flat systems are placed on a page, the resulting
vertical spacing may be non-elegant: one system at the top of the page,
and the other at the bottom, with a huge gap between them.  To avoid this
situation, the space added between the systems can be limited.  This
feature is activated by setting to @code{#t} the
@code{page-limit-inter-system-space} variable in the @code{\paper}
block.  The paper variable @code{page-limit-inter-system-space-factor}
determines how much the space can be increased: for instance, the value
@code{1.3} means that the space can be 30% larger than what it would be
on a ragged-bottom page.

In the following example, if the inter system space were not limited,
the second system of page 1 would be placed at the page bottom.  By
activating the space limitation, the second system is placed closer to
the first one.  By setting @code{page-limit-inter-system-space-factor} to
@code{1}, the spacing would the same as on a ragged-bottom page, like
the last one.

@lilypond[verbatim]
#(set-default-paper-size "a6")
\book {
  \paper {
    page-limit-inter-system-space = ##t
    page-limit-inter-system-space-factor = 1.3

    oddFooterMarkup = \markup "page bottom"
    evenFooterMarkup = \markup "page bottom"
    oddHeaderMarkup = \markup \fill-line {
      "page top" \fromproperty #'page:page-number-string }
    evenHeaderMarkup = \markup \fill-line {
      "page top" \fromproperty #'page:page-number-string }
  }
  \new Staff << \repeat unfold 4 { g'4 g' g' g' \break }
                { s1*2 \pageBreak } >>
}
@end lilypond


@seealso
Snippets:
@rlsr{Spacing}.


@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 five different settings:

@itemize
@item @code{X-offset}
@item @code{Y-offset}
@item @code{alignment-offsets}
@item @code{alignment-extra-space}
@item @code{fixed-alignment-extra-space}
@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-offsets . (0 -15)))

\overrideProperty NonMusicalPaperColumn
  #'line-break-system-details #'((X-offset . 20) (Y-offset . 40)
                                 (alignment-offsets . (0 -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 startpoint of each staff
within each system manually.  We do this using the @code{alignment-offsets}
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-offsets . (0 -15)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 60)
                                           (alignment-offsets . (0 -15)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 100)
                                           (alignment-offsets . (0 -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-offsets} pairs to control the vertical startpoint of
every system and every staff.  Finally, note that @code{alignment-offsets}
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-offsets . (0 -30 -40)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 60)
                                           (alignment-offsets . (0 -10 -20)))
          s1*5 \break
          \overrideProperty #"Score.NonMusicalPaperColumn"
            #'line-break-system-details #'((Y-offset . 100)
                                           (alignment-offsets . (0 -10 -40)))
          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-offsets}, lyrics count as a staff.

@item The units of the numbers passed to @code{X-offset},
@code{Y-offset} and @code{alignment-offsets} 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,fragment,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,fragment,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 staffs 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,fragment,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,fragment,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,fragment,verbatim,relative=2]
c2 c4. c8 c4. c16[ c] c4. c8 c8 c8 c4 c4 c4
@end lilypond


In the introduction
FIXME FIXME FIXME
@c (see @rlearning{Engraving}), 
it was explained that stem
directions influence 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,fragment,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,relative=2,fragment,verbatim]
\new Score \with {
  \override SpacingSpanner #'uniform-stretching = ##t
} <<
  \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
    }
  }
>>
@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,fragment,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]
\new 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]
\new Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 20)
} <<
  \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

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}.  Recall that context settings appear in one of
three locations in 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}.

The @code{proportionalNotationDuration} setting takes a single argument,
which is the reference duration against which all music will be
spaced.  The LilyPond Scheme function 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.  The values
@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]
\new Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 8)
} <<
  \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 Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 16)
} <<
  \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 Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 32)
} <<
  \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

Note that too large a reference duration -- such as the eighth note,
above -- spaces music too tightly and can cause note head collisions.
Note also that proportional notation in general takes up more
horizontal space that does 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]
\new 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 notes of the bottom staff do not
stretch uniformly.  Classical engraving includes very few complex
triplets and so classical engraving rules can generate this type of
result.  Setting @code{proportionalNotationDuration} remedies this
situation considerably.

@lilypond[quote,verbatim,ragged-right]
\new Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 20)
} <<
  \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

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 do 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]
\new Score \with {
  proportionalNotationDuration = #(ly:make-moment 1 20)
  \override SpacingSpanner #'uniform-stretching = ##t
} <<
  \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

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 @{
  between-system-padding = #0.1
  between-system-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
\override DynamicText #'extra-offset = #'( -2.2 . 2.0)
e4 c g\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}.