@c -*- coding: utf-8; mode: texinfo; -*- @c This file is part of lilypond.tely @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 @node Changing defaults @chapter Changing defaults The purpose of LilyPond's design is to provide the finest output quality as a default. Nevertheless, it may happen that you need to change this default layout. The layout is controlled through a large number of proverbial @q{knobs and switches.} This chapter does not list each and every knob. Rather, it outlines what groups of controls are available and explains how to lookup which knob to use for a particular effect. @cindex Internals Reference The controls available for tuning are described in a separate document, the @iftex Internals Reference manual. @end iftex @ifnottex @ref{Top,Internals Reference,,lilypond-internals}. @end ifnottex That manual lists all different variables, functions and options available in LilyPond. It is written as a HTML document, which is available @c leave the @uref as one long line. @uref{http://@/lilypond@/.org/@/doc/@/stable/@/Documentation/@/user/@/lilypond@/-internals/,on@/-line}, but is also included with the LilyPond documentation package. There are four areas where the default settings may be changed: @itemize @item Automatic notation: changing the automatic creation of notation elements. For example, changing the beaming rules. @item Output: changing the appearance of individual objects. For example, changing stem directions or the location of subscripts. @item Context: changing aspects of the translation from music events to notation. For example, giving each staff a separate time signature. @item Page layout: changing the appearance of the spacing, line breaks, and page dimensions. These modifications are discussed in @ref{Non-musical notation}, and @ref{Spacing issues}. @end itemize Internally, LilyPond uses Scheme (a LISP dialect) to provide infrastructure. Overriding layout decisions in effect accesses the program internals, which requires Scheme input. Scheme elements are introduced in a @code{.ly} file with the hash mark @code{#}.@footnote{@rlearning{Scheme tutorial}, contains a short tutorial on entering numbers, lists, strings, and symbols in Scheme.} @menu * Interpretation contexts:: * The \override command:: @end menu @node Interpretation contexts @section Interpretation contexts This section describes what contexts are, and how to modify them. @menu * Contexts explained:: * Creating contexts:: * Changing context properties on the fly:: * Modifying context plug-ins:: * Layout tunings within contexts:: * Changing context default settings:: * Defining new contexts:: * Aligning contexts:: * Vertical grouping of grobs:: @end menu @node Contexts explained @subsection Contexts explained When music is printed, a lot of notational elements must be added to the output. For example, compare the input and output of the following example: @lilypond[quote,verbatim,relative=2,fragment] cis4 cis2. g4 @end lilypond The input is rather sparse, but in the output, bar lines, accidentals, clef, and time signature are added. LilyPond @emph{interprets} the input. During this step, the musical information is inspected in time order, similar to reading a score from left to right. While reading the input, the program remembers where measure boundaries are, and which pitches require explicit accidentals. This information can be presented on several levels. For example, the effect of an accidental is limited to a single staff, while a bar line must be synchronized across the entire score. Within LilyPond, these rules and bits of information are grouped in @emph{Contexts}. Some examples of contexts are @code{Voice}, @code{Staff}, and @code{Score}. They are hierarchical, for example: a @code{Staff} can contain many @code{Voice}s, and a @code{Score} can contain many @code{Staff} contexts. @quotation @sourceimage{context-example,5cm,,} @end quotation Each context has the responsibility for enforcing some notation rules, creating some notation objects and maintaining the associated properties. For example, the @code{Voice} context may introduce an accidental and then the @code{Staff} context maintains the rule to show or suppress the accidental for the remainder of the measure. The synchronization of bar lines is handled at @code{Score} context. However, in some music we may not want the bar lines to be synchronized -- consider a polymetric score in 4/4 and 3/4 time. In such cases, we must modify the default settings of the @code{Score} and @code{Staff} contexts. For very simple scores, contexts are created implicitly, and you need not be aware of them. For larger pieces, such as anything with more than one staff, they must be created explicitly to make sure that you get as many staves as you need, and that they are in the correct order. For typesetting pieces with specialized notation, it can be useful to modify existing or to define new contexts. A complete description of all available contexts is in the program reference, see @ifhtml @internalsref{Contexts}. @end ifhtml @ifnothtml Translation @expansion{} Context. @end ifnothtml @c [TODO: describe propagation] @node Creating contexts @subsection Creating contexts For scores with only one voice and one staff, contexts are created automatically. For more complex scores, it is necessary to create them by hand. There are three commands that do this. @itemize @item The easiest command is @code{\new}, and it also the quickest to type. It is prepended to a music expression, for example @funindex \new @cindex new contexts @cindex Context, creating @example \new @var{type} @var{music expression} @end example @noindent where @var{type} is a context name (like @code{Staff} or @code{Voice}). This command creates a new context, and starts interpreting the @var{music expression} with that. A practical application of @code{\new} is a score with many staves. Each part that should be on its own staff, is preceded with @code{\new Staff}. @lilypond[quote,verbatim,relative=2,ragged-right,fragment] << \new Staff { c4 c } \new Staff { d4 d } >> @end lilypond The @code{\new} command may also give a name to the context, @example \new @var{type} = @var{id} @var{music} @end example However, this user specified name is only used if there is no other context already earlier with the same name. @funindex \context @item Like @code{\new}, the @code{\context} command also directs a music expression to a context object, but gives the context an explicit name. The syntax is @example \context @var{type} = @var{id} @var{music} @end example This form will search for an existing context of type @var{type} called @var{id}. If that context does not exist yet, a new context with the specified name is created. This is useful if the context is referred to later on. For example, when setting lyrics the melody is in a named context @example \context Voice = "@b{tenor}" @var{music} @end example @noindent so the texts can be properly aligned to its notes, @example \new Lyrics \lyricsto "@b{tenor}" @var{lyrics} @end example @noindent Another possible use of named contexts is funneling two different music expressions into one context. In the following example, articulations and notes are entered separately, @example music = @{ c4 c4 @} arts = @{ s4-. s4-> @} @end example They are combined by sending both to the same @code{Voice} context, @example << \new Staff \context Voice = "A" \music \context Voice = "A" \arts >> @end example @lilypond[quote,ragged-right] music = { c4 c4 } arts = { s4-. s4-> } \relative c'' << \new Staff \context Voice = "A" \music \context Voice = "A" \arts >> @end lilypond With this mechanism, it is possible to define an Urtext (original edition), with the option to put several distinct articulations on the same notes. @cindex creating contexts @item The third command for creating contexts is @example \context @var{type} @var{music} @end example @noindent This is similar to @code{\context} with @code{= @var{id}}, but matches any context of type @var{type}, regardless of its given name. This variant is used with music expressions that can be interpreted at several levels. For example, the @code{\applyOutput} command (see @ref{Running a function on all layout objects}). Without an explicit @code{\context}, it is usually applied to @code{Voice} @example \applyOutput #'@var{context} #@var{function} % apply to Voice @end example To have it interpreted at the @code{Score} or @code{Staff} level use these forms @example \applyOutput #'Score #@var{function} \applyOutput #'Staff #@var{function} @end example @end itemize @node Changing context properties on the fly @subsection Changing context properties on the fly @cindex properties @funindex \set @cindex changing properties Each context can have different @emph{properties}, variables contained in that context. They can be changed during the interpretation step. This is achieved by inserting the @code{\set} command in the music, @example \set @var{context}.@var{prop} = #@var{value} @end example For example, @lilypond[quote,verbatim,relative=2,fragment] R1*2 \set Score.skipBars = ##t R1*2 @end lilypond This command skips measures that have no notes. The result is that multi-rests are condensed. The value assigned is a Scheme object. In this case, it is @code{#t}, the boolean True value. If the @var{context} argument is left out, then the current bottom-most context (typically @code{ChordNames}, @code{Voice}, or @code{Lyrics}) is used. In this example, @lilypond[quote,verbatim,relative=2,fragment] c8 c c c \set autoBeaming = ##f c8 c c c @end lilypond @noindent the @var{context} argument to @code{\set} is left out, so automatic beaming is switched off in the current @internalsref{Voice}. Note that the bottom-most context does not always contain the property that you wish to change -- for example, attempting to set the @code{skipBars} property (of the bottom-most context, in this case @code{Voice}) will have no effect. @lilypond[quote,verbatim,relative=2,fragment] R1*2 \set skipBars = ##t R1*2 @end lilypond Contexts are hierarchical, so if a bigger context was specified, for example @code{Staff}, then the change would also apply to all @code{Voice}s in the current stave. The change is applied @q{on-the-fly}, during the music, so that the setting only affects the second group of eighth notes. @funindex \unset There is also an @code{\unset} command, @example \unset @var{context}.@var{prop} @end example @noindent which removes the definition of @var{prop}. This command removes the definition only if it is set in @var{context}, so @example \set Staff.autoBeaming = ##f @end example @noindent introduces a property setting at @code{Staff} level. The setting also applies to the current @code{Voice}. However, @example \unset Voice.autoBeaming @end example @noindent does not have any effect. To cancel this setting, the @code{\unset} must be specified on the same level as the original @code{\set}. In other words, undoing the effect of @code{Staff.autoBeaming = ##f} requires @example \unset Staff.autoBeaming @end example Like @code{\set}, the @var{context} argument does not have to be specified for a bottom context, so the two statements @example \set Voice.autoBeaming = ##t \set autoBeaming = ##t @end example @noindent are equivalent. @cindex \once Settings that should only apply to a single time-step can be entered with @code{\once}, for example in @lilypond[quote,verbatim,relative=2,fragment] c4 \once \set fontSize = #4.7 c4 c4 @end lilypond the property @code{fontSize} is unset automatically after the second note. A full description of all available context properties is in the program reference, see @ifhtml @internalsref{Tunable context properties}. @end ifhtml @ifnothtml Translation @expansion{} Tunable context properties. @end ifnothtml @node Modifying context plug-ins @subsection Modifying context plug-ins Notation contexts (like @code{Score} and @code{Staff}) not only store properties, they also contain plug-ins called @q{engravers} that create notation elements. For example, the @code{Voice} context contains a @code{Note_head_engraver} and the @code{Staff} context contains a @code{Key_signature_engraver}. For a full a description of each plug-in, see @ifhtml @internalsref{Engravers}. @end ifhtml @ifnothtml Internals Reference @expansion{} Translation @expansion{} Engravers. @end ifnothtml Every context described in @ifhtml @internalsref{Contexts} @end ifhtml @ifnothtml Internals Reference @expansion{} Translation @expansion{} Context. @end ifnothtml lists the engravers used for that context. It can be useful to shuffle around these plug-ins. This is done by starting a new context with @code{\new} or @code{\context}, and modifying it, @funindex \with @example \new @var{context} \with @{ \consists @dots{} \consists @dots{} \remove @dots{} \remove @dots{} @emph{etc.} @} @{ @emph{..music..} @} @end example @noindent where the @dots{} should be the name of an engraver. Here is a simple example which removes @code{Time_signature_engraver} and @code{Clef_engraver} from a @code{Staff} context, @lilypond[quote,relative=1,verbatim,fragment] << \new Staff { f2 g } \new Staff \with { \remove "Time_signature_engraver" \remove "Clef_engraver" } { f2 g2 } >> @end lilypond In the second staff there are no time signature or clef symbols. This is a rather crude method of making objects disappear since it will affect the entire staff. This method also influences the spacing, which may or may not be desirable. A more sophisticated method of blanking objects is shown in @rlearning{Common tweaks}. The next example shows a practical application. Bar lines and time signatures are normally synchronized across the score. This is done by the @code{Timing_translator} and @code{Default_bar_line_engraver}. This plug-in keeps an administration of time signature, location within the measure, etc. By moving thes engraver from @code{Score} to @code{Staff} context, we can have a score where each staff has its own time signature. @cindex polymetric scores @cindex Time signatures, multiple @lilypond[quote,relative=1,ragged-right,verbatim,fragment] \new Score \with { \remove "Timing_translator" \remove "Default_bar_line_engraver" } << \new Staff \with { \consists "Timing_translator" \consists "Default_bar_line_engraver" } { \time 3/4 c4 c c c c c } \new Staff \with { \consists "Timing_translator" \consists "Default_bar_line_engraver" } { \time 2/4 c4 c c c c c } >> @end lilypond @node Layout tunings within contexts @subsection Layout tunings within contexts Each context is responsible for creating certain types of graphical objects. The settings used for printing these objects are also stored by context. By changing these settings, the appearance of objects can be altered. The syntax for this is @example \override @var{context}.@var{name} #'@var{property} = #@var{value} @end example Here @var{name} is the name of a graphical object, like @code{Stem} or @code{NoteHead}, and @var{property} is an internal variable of the formatting system (@q{grob property} or @q{layout property}). The latter is a symbol, so it must be quoted. The subsection @ref{Constructing a tweak}, explains what to fill in for @var{name}, @var{property}, and @var{value}. Here we only discuss the functionality of this command. The command @verbatim \override Staff.Stem #'thickness = #4.0 @end verbatim @noindent makes stems thicker (the default is 1.3, with staff line thickness as a unit). Since the command specifies @code{Staff} as context, it only applies to the current staff. Other staves will keep their normal appearance. Here we see the command in action: @lilypond[quote,verbatim,relative=2,fragment] c4 \override Staff.Stem #'thickness = #4.0 c4 c4 c4 @end lilypond The @code{\override} command changes the definition of the @code{Stem} within the current @code{Staff}. After the command is interpreted all stems are thickened. Analogous to @code{\set}, the @var{context} argument may be left out, causing the default context @code{Voice} to be used. Adding @code{\once} applies the change during one timestep only. @lilypond[quote,fragment,verbatim,relative=2] c4 \once \override Stem #'thickness = #4.0 c4 c4 @end lilypond The @code{\override} must be done before the object is started. Therefore, when altering @emph{Spanner} objects such as slurs or beams, the @code{\override} command must be executed at the moment when the object is created. In this example, @lilypond[quote,fragment,verbatim,relative=2] \override Slur #'thickness = #3.0 c8[( c \override Beam #'thickness = #0.6 c8 c]) @end lilypond @noindent the slur is fatter but the beam is not. This is because the command for @code{Beam} comes after the Beam is started, so it has no effect. Analogous to @code{\unset}, the @code{\revert} command for a context undoes an @code{\override} command; like with @code{\unset}, it only affects settings that were made in the same context. In other words, the @code{\revert} in the next example does not do anything. @example \override Voice.Stem #'thickness = #4.0 \revert Staff.Stem #'thickness @end example Some tweakable options are called @q{subproperties} and reside inside properties. To tweak those, use commands of the form @c leave this as a long long @example \override @var{context}.@var{name} #'@var{property} #'@var{subproperty} = #@var{value} @end example @noindent such as @example \override Stem #'details #'beamed-lengths = #'(4 4 3) @end example @seealso Internals: @internalsref{OverrideProperty}, @internalsref{RevertProperty}, @internalsref{PropertySet}, @internalsref{Backend}, and @internalsref{All layout objects}. @refbugs The back-end is not very strict in type-checking object properties. Cyclic references in Scheme values for properties can cause hangs or crashes, or both. @node Changing context default settings @subsection Changing context default settings The adjustments of the previous subsections (@ref{Changing context properties on the fly}, @ref{Modifying context plug-ins}, and @ref{Layout tunings within contexts}) can also be entered separately from the music in the @code{\layout} block, @example \layout @{ @dots{} \context @{ \Staff \set fontSize = #-2 \override Stem #'thickness = #4.0 \remove "Time_signature_engraver" @} @} @end example The @code{\Staff} command brings in the existing definition of the staff context so that it can be modified. The statements @example \set fontSize = #-2 \override Stem #'thickness = #4.0 \remove "Time_signature_engraver" @end example @noindent affect all staves in the score. Other contexts can be modified analogously. The @code{\set} keyword is optional within the @code{\layout} block, so @example \context @{ @dots{} fontSize = #-2 @} @end example @noindent will also work. @refbugs It is not possible to collect context changes in a variable and apply them to a @code{\context} definition by referring to that variable. The @code{\RemoveEmptyStaffContext} will overwrite your current @code{\Staff} settings. If you wish to change the defaults for a staff which uses @code{\RemoveEmptyStaffContext}, you must do so after calling @code{\RemoveEmptyStaffContext}, ie @example \layout @{ \context @{ \RemoveEmptyStaffContext \override Stem #'thickness = #4.0 @} @} @end example @node Defining new contexts @subsection Defining new contexts Specific contexts, like @code{Staff} and @code{Voice}, are made of simple building blocks. It is possible to create new types of contexts with different combinations of engraver plug-ins. The next example shows how to build a different type of @code{Voice} context from scratch. It will be similar to @code{Voice}, but only prints centered slash note heads. It can be used to indicate improvisation in jazz pieces, @lilypond[quote,ragged-right] \layout { \context { \name ImproVoice \type "Engraver_group" \consists "Note_heads_engraver" \consists "Text_engraver" \consists Pitch_squash_engraver squashedPosition = #0 \override NoteHead #'style = #'slash \override Stem #'transparent = ##t \alias Voice } \context { \Staff \accepts "ImproVoice" }} \relative c'' { a4 d8 bes8 \new ImproVoice { c4^"ad lib" c c4 c^"undress" c_"while playing :)" c } a1 } @end lilypond These settings are defined within a @code{\context} block inside a @code{\layout} block, @example \layout @{ \context @{ @dots{} @} @} @end example In the following discussion, the example input shown should go in place of the @dots{} in the previous fragment. First it is necessary to define a name for the new context: @example \name ImproVoice @end example Since it is similar to the @code{Voice}, we want commands that work on (existing) @code{Voice}s to remain working. This is achieved by giving the new context an alias @code{Voice}, @example \alias Voice @end example The context will print notes and instructive texts, so we need to add the engravers which provide this functionality, @example \consists Note_heads_engraver \consists Text_engraver @end example but we only need this on the center line, @example \consists Pitch_squash_engraver squashedPosition = #0 @end example The @internalsref{Pitch_squash_engraver} modifies note heads (created by @internalsref{Note_heads_engraver}) and sets their vertical position to the value of @code{squashedPosition}, in this case@tie{}@code{0}, the center line. The notes look like a slash, and have no stem, @example \override NoteHead #'style = #'slash \override Stem #'transparent = ##t @end example All these plug-ins have to cooperate, and this is achieved with a special plug-in, which must be marked with the keyword @code{\type}. This should always be @internalsref{Engraver_group}, @example \type "Engraver_group" @end example Put together, we get @example \context @{ \name ImproVoice \type "Engraver_group" \consists "Note_heads_engraver" \consists "Text_engraver" \consists Pitch_squash_engraver squashedPosition = #0 \override NoteHead #'style = #'slash \override Stem #'transparent = ##t \alias Voice @} @end example @funindex \accepts Contexts form hierarchies. We want to hang the @code{ImproVoice} under @code{Staff}, just like normal @code{Voice}s. Therefore, we modify the @code{Staff} definition with the @code{\accepts} command, @example \context @{ \Staff \accepts ImproVoice @} @end example @funindex \denies The opposite of @code{\accepts} is @code{\denies}, which is sometimes needed when reusing existing context definitions. Putting both into a @code{\layout} block, like @example \layout @{ \context @{ \name ImproVoice @dots{} @} \context @{ \Staff \accepts "ImproVoice" @} @} @end example Then the output at the start of this subsection can be entered as @example \relative c'' @{ a4 d8 bes8 \new ImproVoice @{ c4^"ad lib" c c4 c^"undress" c c_"while playing :)" @} a1 @} @end example @node Aligning contexts @subsection Aligning contexts New contexts may be aligned above or below exisiting contexts. This could be useful in setting up a vocal staff (@rlearning{Vocal ensembles}) and in ossia, FIXME: this section doens't work in pdf. (?) @cindex ossia @findex alignAboveContext @findex alignBelowContext @lilypond[quote,ragged-right] ossia = { f4 f f f } \score{ \relative c' \new Staff = "main" { c4 c c c << \new Staff \with {alignAboveContext=main} \ossia { d8 f d f d f d f } >> } } @end lilypond @node Vertical grouping of grobs @subsection Vertical grouping of grobs The VerticalAlignment and VerticalAxisGroup grobs work together. VerticalAxisGroup groups together different grobs like Staff, Lyrics, etc. VerticalAlignment then vertically aligns the different grobs grouped together by VerticalAxisGroup. There is usually only one VerticalAlignment per score but every Staff, Lyrics, etc. has its own VerticalAxisGroup. @node The \override command @section The @code{\override} command In the previous section, we have already touched on a command that changes layout details: the @code{\override} command. In this section, we will look in more detail at how to use the command in practice. The general syntax of this command is: @example \override @var{context}.@var{layout_object} #'@var{layout_property} = #@var{value} @end example This will set the @var{layout_property} of the specified @var{layout_object}, which is a member of the @var{context}, to the @var{value}. @menu * Constructing a tweak:: * Navigating the program reference:: * Layout interfaces:: * Determining the grob property:: * Objects connected to the input:: * Using Scheme code instead of \tweak:: * \set versus \override:: * Difficult tweaks:: @end menu @node Constructing a tweak @subsection Constructing a tweak Commands which change output generally look like @example \override Voice.Stem #'thickness = #3.0 @end example @noindent To construct this tweak we must determine these bits of information: @itemize @item the context: here @code{Voice}. @item the layout object: here @code{Stem}. @item the layout property: here @code{thickness}. @item a sensible value: here @code{3.0}. @end itemize Some tweakable options are called @q{subproperties} and reside inside properties. To tweak those, use commands in the form @example \override Stem #'details #'beamed-lengths = #'(4 4 3) @end example @cindex internal documentation @cindex finding graphical objects @cindex graphical object descriptions @cindex tweaking @funindex \override @cindex internal documentation For many properties, regardless of the data type of the property, setting the property to false ( @code{##f} ) will result in turning it off, causing Lilypond to ignore that property entirely. This is particularly useful for turning off grob properties which may otherwise be causing problems. We demonstrate how to glean this information from the notation manual and the program reference. @node Navigating the program reference @subsection Navigating the program reference Suppose we want to move the fingering indication in the fragment below: @lilypond[quote,fragment,relative=2,verbatim] c-2 \stemUp f @end lilypond If you visit the documentation on fingering instructions (in @ref{Fingering instructions}), you will notice: @quotation @seealso Internals Reference: @internalsref{Fingering}. @end quotation @c outdated info; probably will delete. @ignore This fragment points to two parts of the program reference: a page on @code{FingerEvent} and one on @code{Fingering}. The page on @code{FingerEvent} describes the properties of the music expression for the input @code{-2}. The page contains many links forward. For example, it says @quotation Accepted by: @internalsref{Fingering_engraver}, @end quotation @noindent That link brings us to the documentation for the Engraver, the plug-in, which says @quotation This engraver creates the following layout objects: @internalsref{Fingering}. @end quotation In other words, once the @code{FingerEvent}s are interpreted, the @code{Fingering_engraver} plug-in will process them. @end ignore @ignore @c I can't figure out what this is supposed to mean. -gp The @code{Fingering_engraver} is also listed to create @internalsref{Fingering} objects, @c old info? it doesn't make any sense to me with our current docs. This is also the second bit of information listed under @b{See also} in the Notation manual. @end ignore @ifnothtml The programmer's reference is available as an HTML document. It is highly recommended that you read it in HTML form, either online or by downloading the HTML documentation. This section will be much more difficult to understand if you are using the PDF manual. @end ifnothtml Follow the link to @internalsref{Fingering}. At the top of the page, you will see @quotation Fingering objects are created by: @internalsref{Fingering_engraver} and @internalsref{New_fingering_engraver}. @end quotation By following related links inside the program reference, we can follow the flow of information within the program: @itemize @item @internalsref{Fingering}: @internalsref{Fingering} objects are created by: @internalsref{Fingering_engraver} @item @internalsref{Fingering_engraver}: Music types accepted: @internalsref{fingering-event} @item @internalsref{fingering-event}: Music event type @code{fingering-event} is in Music expressions named @internalsref{FingerEvent} @end itemize This path goes against the flow of information in the program: it starts from the output, and ends at the input event. You could also start at an input event, and read with the flow of information, eventually ending up at the output object(s). The program reference can also be browsed like a normal document. It contains chapters on @ifhtml @internalsref{Music definitions}, @end ifhtml @ifnothtml @code{Music definitions} @end ifnothtml on @internalsref{Translation}, and the @internalsref{Backend}. Every chapter lists all the definitions used and all properties that may be tuned. @node Layout interfaces @subsection Layout interfaces @cindex interface, layout @cindex layout interface @cindex grob The HTML page that we found in the previous section describes the layout object called @internalsref{Fingering}. Such an object is a symbol within the score. It has properties that store numbers (like thicknesses and directions), but also pointers to related objects. A layout object is also called a @emph{Grob}, which is short for Graphical Object. For more details about Grobs, see @internalsref{grob-interface}. The page for @code{Fingering} lists the definitions for the @code{Fingering} object. For example, the page says @quotation @code{padding} (dimension, in staff space): @code{0.5} @end quotation @noindent which means that the number will be kept at a distance of at least 0.5 of the note head. Each layout object may have several functions as a notational or typographical element. For example, the Fingering object has the following aspects @itemize @item Its size is independent of the horizontal spacing, unlike slurs or beams. @item It is a piece of text. Granted, it is usually a very short text. @item That piece of text is typeset with a font, unlike slurs or beams. @item Horizontally, the center of the symbol should be aligned to the center of the note head. @item Vertically, the symbol is placed next to the note and the staff. @item The vertical position is also coordinated with other superscript and subscript symbols. @end itemize Each of these aspects is captured in so-called @emph{interface}s, which are listed on the @internalsref{Fingering} page at the bottom @quotation This object supports the following interfaces: @internalsref{item-interface}, @internalsref{self-alignment-interface}, @internalsref{side-position-interface}, @internalsref{text-interface}, @internalsref{text-script-interface}, @internalsref{font-interface}, @internalsref{finger-interface}, and @internalsref{grob-interface}. @end quotation Clicking any of the links will take you to the page of the respective object interface. Each interface has a number of properties. Some of them are not user-serviceable (@q{Internal properties}), but others can be modified. We have been talking of @emph{the} @code{Fingering} object, but actually it does not amount to much. The initialization file (see @rlearning{Default files}) @file{scm/@/define@/-grobs@/.scm} shows the soul of the @q{object}, @example (Fingering . ((padding . 0.5) (avoid-slur . around) (slur-padding . 0.2) (staff-padding . 0.5) (self-alignment-X . 0) (self-alignment-Y . 0) (script-priority . 100) (stencil . ,ly:text-interface::print) (direction . ,ly:script-interface::calc-direction) (font-encoding . fetaNumber) (font-size . -5) ; don't overlap when next to heads. (meta . ((class . Item) (interfaces . (finger-interface font-interface text-script-interface text-interface side-position-interface self-alignment-interface item-interface)))))) @end example @noindent As you can see, the @code{Fingering} object is nothing more than a bunch of variable settings, and the webpage in the Internals Reference is directly generated from this definition. @node Determining the grob property @subsection Determining the grob property Recall that we wanted to change the position of the @b{2} in @lilypond[quote,fragment,relative=2,verbatim] c-2 \stemUp f @end lilypond Since the @b{2} is vertically positioned next to its note, we have to meddle with the interface associated with this positioning. This is done using @code{side-position-interface}. The page for this interface says @quotation @code{side-position-interface} Position a victim object (this one) next to other objects (the support). The property @code{direction} signifies where to put the victim object relative to the support (left or right, up or down?) @end quotation @cindex padding @noindent Below this description, the variable @code{padding} is described as @quotation @table @code @item padding (dimension, in staff space) Add this much extra space between objects that are next to each other. @end table @end quotation By increasing the value of @code{padding}, we can move the fingering away from the note head. The following command inserts 3 staff spaces of white between the note and the fingering: @example \once \override Voice.Fingering #'padding = #3 @end example Inserting this command before the Fingering object is created, i.e., before @code{c2}, yields the following result: @lilypond[quote,relative=2,fragment,verbatim] \once \override Voice.Fingering #'padding = #3 c-2 \stemUp f @end lilypond In this case, the context for this tweak is @code{Voice}. This fact can also be deduced from the program reference, for the page for the @internalsref{Fingering_engraver} plug-in says @quotation Fingering_engraver is part of contexts: @dots{} @internalsref{Voice} @end quotation @node Objects connected to the input @subsection Objects connected to the input @funindex \tweak In some cases, it is possible to take a short-cut for tuning graphical objects. For objects that result directly from a piece of the input, you can use the @code{\tweak} function, for example @lilypond[relative=2,fragment,verbatim,ragged-right] < c \tweak #'color #red d g \tweak #'duration-log #1 a >4-\tweak #'padding #10 -. @end lilypond As you can see, properties are set in the objects directly, without mentioning the grob name or context where this should be applied. This technique only works for objects that are directly connected to an @internalsref{Event} from the input, for example @itemize @item note heads, caused by chord-pitch (i.e., notes inside a chord) @item articulation signs, caused by articulation instructions @end itemize It notably does not work for stems and accidentals (these are caused by note heads, not by music events) or clefs (these are not caused by music inputs, but rather by the change of a property value). There are very few objects which are @emph{directly} connected to output. A normal note (like @code{c4}) is not directly connected to output, so @example \tweak #'color #red c4 @end example @noindent does not change color. See @ref{Displaying music expressions}, for details. @node Using Scheme code instead of \tweak @subsection Using Scheme code instead of @code{\tweak} The main disadvantage of @code{\tweak} is its syntactical inflexibility. For example, the following produces a syntax error. @example F = \tweak #'font-size #-3 -\flageolet \relative c'' @{ c4^\F c4_\F @} @end example @noindent With other words, @code{\tweak} doesn't behave like an articulation regarding the syntax; in particular, it can't be attached with @code{^} and @code{_}. Using Scheme, this problem can be circumvented. The route to the result is given in @ref{Adding articulation to notes (example)}, especially how to use @code{\displayMusic} as a helping guide. @example F = #(let ((m (make-music 'ArticulationEvent 'articulation-type "flageolet"))) (set! (ly:music-property m 'tweaks) (acons 'font-size -3 (ly:music-property m 'tweaks))) m) \relative c'' @{ c4^\F c4_\F @} @end example @noindent Here, the @code{tweaks} properties of the flageolet object @code{m} (created with @code{make-music}) are extracted with @code{ly:music-property}, a new key-value pair to change the font size is prepended to the property list with the @code{acons} Scheme function, and the result is finally written back with @code{set!}. The last element of the @code{let} block is the return value, @code{m} itself. @node \set versus \override @subsection @code{\set} vs. @code{\override} We have seen two methods of changing properties: @code{\set} and @code{\override}. There are actually two different kinds of properties. Contexts can have properties, which are usually named in @code{studlyCaps}. They mostly control the translation from music to notatino, eg. @code{localKeySignature} (for determining whether to print accidentals), @code{measurePosition} (for determining when to print a bar line). Context properties can change value over time while interpreting a piece of music; @code{measurePosition} is an obvious example of this. Context properties are modified with @code{\set}. There is a special type of context property: the element description. These properties are named in @code{StudlyCaps} (starting with capital letters). They contain the @q{default settings} for said graphical object as an association list. See @file{scm/@/define@/-grobs@/.scm} to see what kind of settings there are. Element descriptions may be modified with @code{\override}. @code{\override} is actually a shorthand; @example \override @var{context}.@var{name} #'@var{property} = #@var{value} @end example @noindent is more or less equivalent to @c leave this long line -gp @example \set @var{context}.@var{name} #'@var{property} = #(cons (cons '@var{property} @var{value}) = (length siblings) 2) (eq? (car (last-pair siblings)) grob)) (ly:grob-set-property! grob 'extra-offset '(-2 . 5))))) \relative c'' { \override Tie #'after-line-breaking = #my-callback c1 ~ \break c2 ~ c } @end lilypond @noindent When applying this trick, the new @code{after-line-breaking} callback should also call the old one @code{after-line-breaking}, if there is one. For example, if using this with @code{Hairpin}, @code{ly:hairpin::after-line-breaking} should also be called. @item Some objects cannot be changed with @code{\override} for technical reasons. Examples of those are @code{NonMusicalPaperColumn} and @code{PaperColumn}. They can be changed with the @code{\overrideProperty} function, which works similar to @code{\once \override}, but uses a different syntax. @example \overrideProperty #"Score.NonMusicalPaperColumn" % Grob name #'line-break-system-details % Property name #'((next-padding . 20)) % Value @end example Note, however, that @code{\override}, applied to @code{NoteMusicalPaperColumn} and @code{PaperColumn}, still works as expected within @code{\context} blocks. @end itemize