1 @c -*- coding: utf-8; mode: texinfo; -*-
2 @node Changing defaults
3 @chapter Changing defaults
6 The purpose of LilyPond's design is to provide the finest output
7 quality as a default. Nevertheless, it may happen that you need to
8 change this default layout. The layout is controlled through a large
9 number of proverbial ``knobs and switches.'' This chapter does not
10 list each and every knob. Rather, it outlines what groups of controls
11 are available and explains how to lookup which knob to use for a
15 @cindex Program reference
17 The controls available for tuning are described in a separate
23 @ref{Top,Program reference,,lilypond-internals}.
26 lists all different variables, functions and options available in
27 LilyPond. It is written as a HTML document, which is available
28 @uref{http://@/lilypond@/.org/@/doc/@/v2.5/@/Documentation/@/user/@/out@/-www/@/lilypond@/-internals/,on@/-line},
29 but is also included with the LilyPond documentation package.
31 There are three areas where the default settings may be changed:
35 Output: changing the appearance of individual
36 objects. For example, changing stem directions or the location of
40 Context: changing aspects of the translation from music events to
41 notation. For example, giving each staff a separate time signature.
44 Global layout: changing the appearance of the spacing, line
45 breaks, and page dimensions.
48 Then there are separate systems for typesetting text (like
49 @emph{ritardando}) and selecting different fonts. This chapter also
52 Internally, LilyPond uses Scheme (a LISP dialect) to provide
53 infrastructure. Overriding layout decisions in effect accesses the
54 program internals, which requires Scheme input. Scheme elements are
55 introduced in a @code{.ly} file with the hash mark
56 @code{#}.@footnote{@ref{Scheme tutorial} contains a short tutorial
57 on entering numbers, lists, strings, and symbols in Scheme.}
61 * Interpretation contexts::
62 * The \override command::
66 @node Interpretation contexts
67 @section Interpretation contexts
69 When music is printed, a lot of notational elements must be added to the
70 input, which is often bare bones. For example, compare the input and
71 output of the following example:
73 @lilypond[quote,verbatim,relative=2,fragment]
77 The input is rather sparse, but in the output, bar lines, accidentals,
78 clef, and time signature are added. LilyPond @emph{interprets} the
79 input. During this step, the musical information is inspected in time
80 order, similar to reading a score from left to right. While reading,
81 the input, the program remembers where measure boundaries are, and what
82 pitches need explicit accidentals. This information can be presented on
83 several levels. For example, the effect of an accidental is limited
84 to a single staff, while a bar line must be synchronized across the
87 Within LilyPond, these rules and bits of information are grouped in
88 so-called Contexts. Examples of context are @context{Voice},
89 @context{Staff}, and @context{Score}. They are hierarchical, for
90 example, a @context{Staff} can contain many @context{Voice}s, and a
91 @context{Score} can contain many @context{Staff} contexts.
93 Each context has the responsibility for enforcing some notation rules,
94 creating some notation objects and maintaining the associated
95 properties. So, the synchronization of bar lines is handled at
96 @context{Score} context. The @context{Voice} may introduce an
97 accidental and then the @context{Staff} context maintains the rule to
98 show or suppress the accidental for the remainder of the measure.
100 For simple scores, contexts are created implicitly, and you need not
101 be aware of them. For larger pieces, such as piano music, they must be
102 created explicitly to make sure that you get as many staves as you
103 need, and that they are in the correct order. For typesetting pieces
104 with specialized notation, it can be useful to modify existing or
105 to define new contexts.
108 A complete description of all available contexts is in the program
111 @internalsref{Contexts}.
114 Translation @arrow{} Context.
117 @c [TODO: describe propagation]
121 * Creating contexts::
122 * Changing context properties on the fly::
123 * Modifying context plug-ins::
124 * Layout tunings within contexts::
125 * Changing context default settings::
126 * Defining new contexts::
129 @node Creating contexts
130 @subsection Creating contexts
132 For scores with only one voice and one staff, correct contexts are
133 created automatically. For more complex scores, it is necessary to
134 create them by hand. There are three commands that do this.
136 The easiest command is @code{\new}, and it also the quickest to type.
137 It is prepended to a music expression, for example
141 @cindex Context, creating
144 \new @var{type} @var{music expression}
148 where @var{type} is a context name (like @code{Staff} or
149 @code{Voice}). This command creates a new context, and starts
150 interpreting the @var{music expression} with that.
152 A practical application of @code{\new} is a score with many
153 staves. Each part that should be on its own staff, is preceded with
156 @lilypond[quote,verbatim,relative=2,raggedright,fragment]
157 << \new Staff { c4 c }
162 @cindex @code{\context}
164 Like @code{\new}, the @code{\context} command also directs a music
165 expression to a context object, but gives the context an extra name. The
169 \context @var{type} = @var{id} @var{music}
172 This form will search for an existing context of type @var{type}
173 called @var{id}. If that context does not exist yet, it is created.
174 This is useful if the context is referred to later on. For example, when
175 setting lyrics the melody is in a named context
178 \context Voice = "@b{tenor}" @var{music}
182 so the texts can be properly aligned to its notes,
185 \new Lyrics \lyricsto "@b{tenor}" @var{lyrics}
190 Another possibility is funneling two different music expressions into
191 one context. In the following example, articulations and notes are
196 arts = @{ s4-. s4-> @}
199 They are combined by sending both to the same @context{Voice} context,
202 << \new Staff \context Voice = "A" \music
203 \context Voice = "A" \arts
206 @lilypond[quote,raggedright]
210 \new Staff \context Voice = "A" \music
211 \context Voice = "A" \arts
215 With this mechanism, it is possible to define an Urtext (original
216 edition), with the option to put several distinct articulations on the
219 @cindex creating contexts
221 The third command for creating contexts is
223 \context @var{type} @var{music}
228 This is similar to @code{\context} with @code{= @var{id}}, but matches
229 any context of type @var{type}, regardless of its given name.
231 This variant is used with music expressions that can be interpreted at
232 several levels. For example, the @code{\applyoutput} command (see
233 @ref{Running a function on all layout objects}). Without an explicit
234 @code{\context}, it is usually applied to @context{Voice}
237 \applyoutput #@var{function} % apply to Voice
240 To have it interpreted at the @context{Score} or @context{Staff} level use
244 \context Score \applyoutput #@var{function}
245 \context Staff \applyoutput #@var{function}
249 @node Changing context properties on the fly
250 @subsection Changing context properties on the fly
254 @cindex changing properties
256 Each context can have different @emph{properties}, variables contained
257 in that context. They can be changed during the interpretation step.
258 This is achieved by inserting the @code{\set} command in the music,
261 \set @var{context}.@var{prop} = #@var{value}
265 @lilypond[quote,verbatim,relative=2,fragment]
267 \set Score.skipBars = ##t
271 This command skips measures that have no notes. The result is that
272 multi-rests are condensed. The value assigned is a Scheme object. In
273 this case, it is @code{#t}, the boolean True value.
275 If the @var{context} argument is left out, then the current bottom-most
276 context (typically @context{ChordNames}, @context{Voice}, or
277 @context{Lyrics}) is used. In this example,
279 @lilypond[quote,verbatim,relative=2,fragment]
281 \set autoBeaming = ##f
286 the @var{context} argument to @code{\set} is left out, so automatic
287 beaming is switched off in the current @internalsref{Voice}. Note that
288 the bottom-most context does not always contain the property that you
289 wish to change -- for example, attempting to set the @code{skipBars}
290 property (of the bottom-most context, in this case @code{Voice}) will
293 @lilypond[quote,verbatim,relative=2,fragment]
299 Contexts are hierarchical, so if a bigger context was specified, for
300 example @context{Staff}, then the change would also apply to all
301 @context{Voice}s in the current stave. The change is applied
302 `on-the-fly', during the music, so that the setting only affects the
303 second group of eighth notes.
305 @cindex @code{\unset}
307 There is also an @code{\unset} command,
309 \unset @var{context}.@var{prop}
313 which removes the definition of @var{prop}. This command removes
314 the definition only if it is set in @var{context}, so
317 \set Staff.autoBeaming = ##f
321 introduces a property setting at @code{Staff} level. The setting also
322 applies to the current @code{Voice}. However,
325 \unset Voice.autoBeaming
329 does not have any effect. To cancel this setting, the @code{\unset}
330 must be specified on the same level as the original @code{\set}. In
331 other words, undoing the effect of @code{Staff.autoBeaming = ##f}
334 \unset Staff.autoBeaming
337 Like @code{\set}, the @var{context} argument does not have to be
338 specified for a bottom context, so the two statements
341 \set Voice.autoBeaming = ##t
342 \set autoBeaming = ##t
350 Settings that should only apply to a single time-step can be entered
351 with @code{\once}, for example in
353 @lilypond[quote,verbatim,relative=2,fragment]
355 \once \set fontSize = #4.7
360 the property @code{fontSize} is unset automatically after the second
363 A full description of all available context properties is in the
364 program reference, see
366 @internalsref{Tunable context properties}.
369 Translation @arrow{} Tunable context properties.
373 @node Modifying context plug-ins
374 @subsection Modifying context plug-ins
376 Notation contexts (like Score and Staff) not only store properties,
377 they also contain plug-ins, called ``engravers'' that create notation
378 elements. For example, the Voice context contains a
379 @code{Note_head_engraver} and the Staff context contains a
380 @code{Key_signature_engraver}.
382 For a full a description of each plug-in, see
384 @internalsref{Engravers}.
387 Program reference @arrow Translation @arrow{} Engravers.
389 Every context described in
391 @internalsref{Contexts}
394 Program reference @arrow Translation @arrow{} Context.
396 lists the engravers used for that context.
399 It can be useful to shuffle around these plug-ins. This is done by
400 starting a new context, with @code{\new} or @code{\context}, and
401 modifying it like this,
404 \new @var{context} \with @{
415 where the @dots{} should be the name of an engraver. Here is a simple
416 example which removes @code{Time_signature_engraver} and
417 @code{Clef_engraver} from a @code{Staff} context,
419 @lilypond[quote,relative=1,verbatim,fragment]
424 \remove "Time_signature_engraver"
425 \remove "Clef_engraver"
432 In the second staff there are no time signature or clef symbols. This
433 is a rather crude method of making objects disappear since it will affect
434 the entire staff. The spacing is adversely influenced too. A more
435 sophisticated method of blanking objects is shown in @ref{Common tweaks}.
437 The next example shows a practical application. Bar lines and time
438 signatures are normally synchronized across the score. This is done
439 by the @code{Timing_engraver}. This plug-in keeps an administration of
440 time signature, location within the measure, etc. By moving the
441 @code{Timing_engraver} engraver from @code{Score} to @code{Staff}
442 context, we can have a score where each staff has its own time
445 @cindex polymetric scores
446 @cindex Time signatures, multiple
448 @lilypond[quote,relative=1,raggedright,verbatim,fragment]
450 \remove "Timing_engraver"
453 \consists "Timing_engraver"
459 \consists "Timing_engraver"
468 @node Layout tunings within contexts
469 @subsection Layout tunings within contexts
471 Each context is responsible for creating certain types of graphical
472 objects. The settings used for printing these objects are also stored by
473 context. By changing these settings, the appearance of objects can be
476 The syntax for this is
479 \override @var{context}.@var{name} #'@var{property} = #@var{value}
482 Here @var{name} is the name of a graphical object, like @code{Stem} or
483 @code{NoteHead}, and @var{property} is an internal variable of the
484 formatting system (`grob property' or `layout property'). The latter is a
485 symbol, so it must be quoted. The subsection @ref{Constructing a
486 tweak} explains what to fill in for @var{name}, @var{property}, and
487 @var{value}. Here we only discuss the functionality of this command.
492 \override Staff.Stem #'thickness = #4.0
496 makes stems thicker (the default is 1.3, with staff line thickness as a
497 unit). Since the command specifies @context{Staff} as context, it only
498 applies to the current staff. Other staves will keep their normal
499 appearance. Here we see the command in action:
501 @lilypond[quote,verbatim,relative=2,fragment]
503 \override Staff.Stem #'thickness = #4.0
509 The @code{\override} command changes the definition of the @code{Stem}
510 within the current @context{Staff}. After the command is interpreted
511 all stems are thickened.
513 Analogous to @code{\set}, the @var{context} argument may be left out,
514 causing it to default to @context{Voice}, and adding @code{\once} applies
515 the change during one timestep only
517 @lilypond[quote,fragment,verbatim,relative=2]
519 \once \override Stem #'thickness = #4.0
524 The @code{\override} must be done before the object is
525 started. Therefore, when altering @emph{Spanner} objects, like slurs or
526 beams, the @code{\override} command must be executed at the moment when
527 the object is created. In this example,
530 @lilypond[quote,fragment,verbatim,relative=2]
531 \override Slur #'thickness = #3.0
533 \override Beam #'thickness = #0.6
538 the slur is fatter but the beam is not. This is because the command for
539 @code{Beam} comes after the Beam is started. Therefore it has no effect.
541 Analogous to @code{\unset}, the @code{\revert} command for a context
542 undoes an @code{\override} command; like with @code{\unset}, it only
543 affects settings that were made in the same context. In other words, the
544 @code{\revert} in the next example does not do anything.
547 \override Voice.Stem #'thickness = #4.0
548 \revert Staff.Stem #'thickness
556 Internals: @internalsref{OverrideProperty}, @internalsref{RevertProperty},
557 @internalsref{PropertySet}, @internalsref{Backend}, and
558 @internalsref{All layout objects}.
563 The back-end is not very strict in type-checking object properties.
564 Cyclic references in Scheme values for properties can cause hangs
568 @node Changing context default settings
569 @subsection Changing context default settings
571 The adjustments of the previous subsections (@ref{Changing context
572 properties on the fly}, @ref{Modifying context plug-ins}, and
573 @ref{Layout tunings within contexts}) can also be entered separately
574 from the music, in the @code{\layout} block,
583 \override Stem #'thickness = #4.0
584 \remove "Time_signature_engraver"
595 takes the existing definition for context @context{Staff} from the
596 identifier @code{\Staff}.
601 \override Stem #'thickness = #4.0
602 \remove "Time_signature_engraver"
606 affect all staves in the score.
608 Other contexts can be modified analogously.
610 The @code{\set} keyword is optional within the @code{\layout} block, so
626 It is not possible to collect context changes in a variable, and apply
627 them to one @code{\context} definition by referring to that variable.
629 The @code{\RemoveEmptyStaffContext} will override your current
630 @code{\Staff} variable. If you wish to change the defaults for a
631 staff that uses @code{\RemoveEmptyStaffContext}, you must do so
632 after calling @code{\RemoveemptyStaffContext}, ie
637 \RemoveEmptyStaffContext
639 \override Stem #'thickness = #4.0
645 @node Defining new contexts
646 @subsection Defining new contexts
648 Specific contexts, like @context{Staff} and @code{Voice}, are made of
649 simple building blocks, and it is possible to compose engraver
650 plug-ins in different combinations, thereby creating new types of
653 The next example shows how to build a different type of
654 @context{Voice} context from scratch. It will be similar to
655 @code{Voice}, but prints centered slash noteheads only. It can be used
656 to indicate improvisation in Jazz pieces,
658 @lilypond[quote,raggedright]
661 \type "Engraver_group_engraver"
662 \consists "Note_heads_engraver"
663 \consists "Text_engraver"
664 \consists Pitch_squash_engraver
665 squashedPosition = #0
666 \override NoteHead #'style = #'slash
667 \override Stem #'transparent = ##t
671 \accepts "ImproVoice"
675 a4 d8 bes8 \new ImproVoice { c4^"ad lib" c
676 c4 c^"undress" c_"while playing :)" c }
682 These settings are again done within a @code{\context} block inside a
683 @code{\layout} block,
693 In the following discussion, the example input shown should go on the
694 @dots{} in the previous fragment.
696 First, the context gets a name. Instead of @context{Voice} it
697 will be called @context{ImproVoice},
703 Since it is similar to the @context{Voice}, we want commands that work
704 on (existing) @context{Voice}s to remain working. This is achieved by
705 giving the new context an alias @context{Voice},
711 The context will print notes, and instructive texts
714 \consists Note_heads_engraver
715 \consists Text_engraver
718 but only on the center line,
721 \consists Pitch_squash_engraver
722 squashedPosition = #0
725 The @internalsref{Pitch_squash_engraver} modifies note heads (created
726 by @internalsref{Note_heads_engraver}) and sets their vertical
727 position to the value of @code{squashedPosition}, in this case@tie{}@code{0},
730 The notes look like a slash, without a stem,
733 \override NoteHead #'style = #'slash
734 \override Stem #'transparent = ##t
738 All these plug-ins have to cooperate, and this is achieved with a
739 special plug-in, which must be marked with the keyword @code{\type}.
740 This should always be @internalsref{Engraver_group_engraver},
743 \type "Engraver_group_engraver"
751 \type "Engraver_group_engraver"
752 \consists "Note_heads_engraver"
753 \consists "Text_engraver"
754 \consists Pitch_squash_engraver
755 squashedPosition = #0
756 \override NoteHead #'style = #'slash
757 \override Stem #'transparent = ##t
762 Contexts form hierarchies. We want to hang the @context{ImproVoice}
763 under @context{Staff}, just like normal @code{Voice}s. Therefore, we
764 modify the @code{Staff} definition with the @code{\accepts}
765 command,@footnote{The opposite of @code{\accepts} is @code{\denies},
766 which is sometimes needed when reusing existing context definitions.}
777 Putting both into a @code{\layout} block, like
787 \accepts "ImproVoice"
792 Then the output at the start of this subsection can be entered as
800 c c_"while playing :)"
809 @node The \override command
810 @section The \override command
812 In the previous section, we have already touched on a command that
813 changes layout details: the @code{\override} command. In this section,
814 we will look in more detail at how to use the command in practice.
815 First, we will give a few versatile commands that are sufficient
816 for many situations. The next section will discuss the general use of
822 * Constructing a tweak::
823 * Navigating the program reference::
824 * Layout interfaces::
825 * Determining the grob property::
832 @subsection Common tweaks
834 @c Should we point at ly/property-init.ly ? -gp
835 Some overrides are so common that predefined commands are provided as
836 short-cuts, for example, @code{\slurUp} and @code{\stemDown}. These
837 commands are described in
841 @c @ref{Notation manual},
844 under the sections for slurs and stems
847 The exact tuning possibilities for each type of layout object are
848 documented in the program reference of the respective
849 object. However, many layout objects share properties, which can be
850 used to apply generic tweaks. We mention a few of these:
853 @item The @code{extra-offset} property, which
854 @cindex @code{extra-offset}
855 has a pair of numbers as value, moves objects around in the printout.
856 The first number controls left-right movement; a positive number will
857 move the object to the right. The second number controls up-down
858 movement; a positive number will move it higher. The units of these
859 offsets are staff-spaces. The @code{extra-offset} property is a
860 low-level feature: the formatting engine is completely oblivious to
863 In the following example, the second fingering is moved a little to
864 the left, and 1.8 staff space downwards:
866 @cindex setting object properties
868 @lilypond[quote,fragment,relative=1,verbatim]
871 \once \override Fingering
872 #'extra-offset = #'(-0.3 . -1.8)
877 Setting the @code{transparent} property will cause an object to be printed
878 in `invisible ink': the object is not printed, but all its other
879 behavior is retained. The object still takes up space, it takes part in
880 collisions, and slurs, ties, and beams can be attached to it.
882 @cindex transparent objects
883 @cindex removing objects
884 @cindex hiding objects
885 @cindex invisible objects
886 The following example demonstrates how to connect different voices
887 using ties. Normally, ties only connect two notes in the same
888 voice. By introducing a tie in a different voice,
890 @lilypond[quote,fragment,relative=2]
899 and blanking the first up-stem in that voice, the tie appears to cross
902 @lilypond[quote,fragment,relative=2,verbatim]
904 \once \override Stem #'transparent = ##t
912 The @code{padding} property for objects with
913 @cindex @code{padding}
914 @code{side-position-interface} can be set to increase the distance between
915 symbols that are printed above or below notes. We provide two
916 examples; a more elaborate explanation is in @ref{Constructing a
919 @lilypond[quote,fragment,relative=1,verbatim]
921 \override Script #'padding = #3
925 @lilypond[quote,fragment,relative=1,verbatim]
926 % This will not work, see below:
927 \override MetronomeMark #'padding = #3
931 \override Score.MetronomeMark #'padding = #3
936 Note in the second example how important it is to figure out what
937 context handles a certain object. Since the @code{MetronomeMark} object
938 is handled in the Score context, property changes in the @code{Voice}
939 context will not be noticed.
943 More specific overrides are also possible. The next section
944 discusses in depth how to figure out these statements for yourself.
947 @node Constructing a tweak
948 @subsection Constructing a tweak
950 The general procedure of changing output, that is, entering
954 \override Voice.Stem #'thickness = #3.0
958 means that we have to determine these bits of information:
961 @item the context: here @context{Voice}.
962 @item the layout object: here @code{Stem}.
963 @item the layout property: here @code{thickness}
964 @item a sensible value: here @code{3.0}
968 @cindex internal documentation
969 @cindex finding graphical objects
970 @cindex graphical object descriptions
972 @cindex @code{\override}
973 @cindex internal documentation
975 We demonstrate how to glean this information from the notation manual
976 and the program reference.
978 @node Navigating the program reference
979 @subsection Navigating the program reference
981 Suppose we want to move the fingering indication in the fragment
984 @lilypond[quote,fragment,relative=2,verbatim]
990 If you visit the documentation on fingering instructions (in
991 @ref{Fingering instructions}), you will notice that there is written:
996 Program reference: @internalsref{FingerEvent} and @internalsref{Fingering}.
1002 This fragment points to two parts of the program reference: a page
1003 on @code{FingerEvent} and one on @code{Fingering}.
1005 The page on @code{FingerEvent} describes the properties of the music
1006 expression for the input @code{-2}. The page contains many links
1007 forward. For example, it says
1010 Accepted by: @internalsref{Fingering_engraver},
1014 That link brings us to the documentation for the Engraver, the
1018 This engraver creates the following layout objects: @internalsref{Fingering}.
1021 In other words, once the @code{FingerEvent}s are interpreted, the
1022 @code{Fingering_engraver} plug-in will process them.
1023 The @code{Fingering_engraver} is also listed to create
1024 @internalsref{Fingering} objects,
1027 Lo and behold, that is also the
1028 second bit of information listed under @b{See also} in the Notation
1029 manual. By clicking around in the program reference, we can follow the
1030 flow of information within the program, either forward (like we did
1031 here), or backwards, following links like this:
1035 @item @internalsref{Fingering}:
1036 @internalsref{Fingering} objects are created by:
1037 @b{@internalsref{Fingering_engraver}}
1039 @item @internalsref{Fingering_engraver}:
1040 Music types accepted: @b{@internalsref{fingering-event}}
1042 @item @internalsref{fingering-event}:
1043 Music event type @code{fingering-event} is in Music expressions named
1044 @b{@internalsref{FingerEvent}}
1047 This path goes against the flow of information in the program: it
1048 starts from the output, and ends at the input event.
1050 The program reference can also be browsed like a normal document. It
1051 contains a chapter on
1053 @internalsref{Music definitions},
1056 @code{Music definitions}
1058 on @internalsref{Translation}, and the @internalsref{Backend}. Every
1059 chapter lists all the definitions used, and all properties that may be
1063 @node Layout interfaces
1064 @subsection Layout interfaces
1066 @cindex interface, layout
1067 @cindex layout interface
1069 The HTML page that we found in the previous section, describes the
1070 layout object called @internalsref{Fingering}. Such an object is a
1071 symbol within the score. It has properties that store numbers (like
1072 thicknesses and directions), but also pointers to related objects. A
1073 layout object is also called
1074 @internalsref{grob-interface},
1076 which is short for Graphical Object.
1079 The page for @code{Fingering} lists the definitions for the
1080 @code{Fingering} object. For example, the page says
1083 @code{padding} (dimension, in staff space):
1089 which means that the number will be kept at a distance of at least 0.6
1093 Each layout object may have several functions as a notational or
1094 typographical element. For example, the Fingering object
1095 has the following aspects
1099 Its size is independent of the horizontal spacing, unlike slurs or beams.
1102 It is a piece of text. Granted, it is usually a very short text.
1105 That piece of text is typeset with a font, unlike slurs or beams.
1108 Horizontally, the center of the symbol should be aligned to the
1109 center of the notehead.
1112 Vertically, the symbol is placed next to the note and the staff.
1115 The vertical position is also coordinated with other super- and subscript
1119 Each of these aspects is captured in so-called @emph{interface}s,
1120 which are listed on the @internalsref{Fingering} page at the bottom
1123 This object supports the following interfaces:
1124 @internalsref{item-interface},
1125 @internalsref{self-alignment-interface},
1126 @internalsref{side-position-interface}, @internalsref{text-interface},
1127 @internalsref{text-script-interface}, @internalsref{font-interface},
1128 @internalsref{finger-interface}, and @internalsref{grob-interface}.
1131 Clicking any of the links will take you to the page of the respective
1132 object interface. Each interface has a number of properties. Some of
1133 them are not user-serviceable (``Internal properties''), but others
1136 We have been talking of @emph{the} @code{Fingering} object, but actually it
1137 does not amount to much. The initialization file
1138 @file{scm/@/define@/-grobs@/.scm} shows the soul of the `object',
1142 . ((print-function . ,Text_interface::print)
1144 (staff-padding . 0.6)
1145 (self-alignment-X . 0)
1146 (self-alignment-Y . 0)
1147 (script-priority . 100)
1149 (meta . ((interfaces . (finger-interface font-interface
1150 text-script-interface text-interface
1151 side-position-interface
1152 self-alignment-interface
1153 item-interface))))))
1157 As you can see, the @code{Fingering} object is nothing more than a
1158 bunch of variable settings, and the webpage in the Program Reference
1159 is directly generated from this definition.
1161 @node Determining the grob property
1162 @subsection Determining the grob property
1165 Recall that we wanted to change the position of the @b{2} in
1167 @lilypond[quote,fragment,relative=2,verbatim]
1173 Since the @b{2} is vertically positioned next to its note, we have to
1174 meddle with the interface associated with this positioning. This is
1175 done using @code{side-position-interface}. The page for this interface
1179 @code{side-position-interface}
1181 Position a victim object (this one) next to other objects (the
1182 support). The property @code{direction} signifies where to put the
1183 victim object relative to the support (left or right, up or down?)
1188 below this description, the variable @code{padding} is described as
1193 (dimension, in staff space)
1195 Add this much extra space between objects that are next to each other.
1199 By increasing the value of @code{padding}, we can move away the
1200 fingering. The following command inserts 3 staff spaces of white
1201 between the note and the fingering:
1203 \once \override Voice.Fingering #'padding = #3
1206 Inserting this command before the Fingering object is created,
1207 i.e., before @code{c2}, yields the following result:
1209 @lilypond[quote,relative=2,fragment,verbatim]
1210 \once \override Voice.Fingering #'padding = #3
1217 In this case, the context for this tweak is @context{Voice}. This
1218 fact can also be deduced from the program reference, for the page for
1219 the @internalsref{Fingering_engraver} plug-in says
1222 Fingering_engraver is part of contexts: @dots{} @b{@internalsref{Voice}}
1225 @node Difficult tweaks
1226 @subsection Difficult tweaks
1228 There are two classes of difficult adjustments. First, when there are
1229 several of the same objects at one point, and you want to adjust only
1230 one. For example, if you want to change only one note head in a chord.
1232 In this case, the @code{\applyoutput} function must be used. The
1233 next example defines a Scheme function @code{set-position-font-size}
1234 that sets the @code{font-size} property, but only
1235 on objects that have @internalsref{note-head-interface} and are at the
1238 @lilypond[quote,verbatim]
1239 #(define ((set-position-font-size pos size) grob origin current)
1241 ((interfaces (ly:grob-property grob 'interfaces))
1242 (position (ly:grob-property grob 'staff-position)))
1244 ; is this a note head?
1245 (memq 'note-head-interface interfaces)
1247 ; is the Y coordinate right?
1251 (set! (ly:grob-property grob 'font-size) size))))
1255 \applyoutput #(set-position-font-size -2 4)
1261 A similar technique can be used for accidentals. In that case, the
1262 function should check for @code{accidental-interface}.
1264 Another difficult adjustment is the appearance of spanner objects,
1265 such as slur and tie. Initially, only one of these objects is created,
1266 and they can be adjusted with the normal mechanism. However, in some
1267 cases the spanners cross line breaks. If this happens, these objects
1268 are cloned. A separate object is created for every system that it is
1269 in. These are clones of the original object and inherit all
1270 properties, including @code{\override}s.
1272 In other words, an @code{\override} always affects all pieces of a
1273 broken spanner. To change only one part of a spanner at a line break,
1274 it is necessary to hook into the formatting process. The
1275 @code{after-line-breaking-callback} property contains the Scheme procedure
1276 that is called after the line breaks have been determined, and layout
1277 objects have been split over different systems.
1279 In the following example, we define a procedure
1280 @code{my-callback}. This procedure
1284 determines if we have been split across line breaks
1286 if yes, retrieves all the split objects
1288 checks if we are the last of the split objects
1290 if yes, it sets @code{extra-offset}.
1293 This procedure is installed into @internalsref{Tie}, so the last part
1294 of the broken tie is translated up.
1297 @lilypond[quote,verbatim,raggedright]
1298 #(define (my-callback grob)
1300 ; have we been split?
1301 (orig (ly:grob-original grob))
1303 ; if yes, get the split pieces (our siblings)
1304 (siblings (if (ly:grob? orig)
1305 (ly:spanner-broken-into orig) '() )))
1307 (if (and (>= (length siblings) 2)
1308 (eq? (car (last-pair siblings)) grob))
1309 (ly:grob-set-property! grob 'extra-offset '(-2 . 5)))))
1312 \override Tie #'after-line-breaking-callback =
1319 When applying this trick, the new @code{after-line-breaking-callback}
1320 should also call the old @code{after-line-breaking-callback}, if there
1321 is one. For example, if using this with @code{Slur},
1322 @code{Slur::after_line_breaking} should also be called.