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_translator} and @code{Default_bar_line_engraver}.
440 This plug-in keeps an administration of time signature, location
441 within the measure, etc. By moving thes engraver from @code{Score} to
442 @code{Staff} context, we can have a score where each staff has its own
445 @cindex polymetric scores
446 @cindex Time signatures, multiple
448 @lilypond[quote,relative=1,raggedright,verbatim,fragment]
450 \remove "Timing_translator"
451 \remove "Default_bar_line_engraver"
454 \consists "Timing_translator"
455 \consists "Default_bar_line_engraver"
461 \consists "Timing_translator"
462 \consists "Default_bar_line_engraver"
471 @node Layout tunings within contexts
472 @subsection Layout tunings within contexts
474 Each context is responsible for creating certain types of graphical
475 objects. The settings used for printing these objects are also stored by
476 context. By changing these settings, the appearance of objects can be
479 The syntax for this is
482 \override @var{context}.@var{name} #'@var{property} = #@var{value}
485 Here @var{name} is the name of a graphical object, like @code{Stem} or
486 @code{NoteHead}, and @var{property} is an internal variable of the
487 formatting system (`grob property' or `layout property'). The latter is a
488 symbol, so it must be quoted. The subsection @ref{Constructing a
489 tweak} explains what to fill in for @var{name}, @var{property}, and
490 @var{value}. Here we only discuss the functionality of this command.
495 \override Staff.Stem #'thickness = #4.0
499 makes stems thicker (the default is 1.3, with staff line thickness as a
500 unit). Since the command specifies @context{Staff} as context, it only
501 applies to the current staff. Other staves will keep their normal
502 appearance. Here we see the command in action:
504 @lilypond[quote,verbatim,relative=2,fragment]
506 \override Staff.Stem #'thickness = #4.0
512 The @code{\override} command changes the definition of the @code{Stem}
513 within the current @context{Staff}. After the command is interpreted
514 all stems are thickened.
516 Analogous to @code{\set}, the @var{context} argument may be left out,
517 causing it to default to @context{Voice}, and adding @code{\once} applies
518 the change during one timestep only
520 @lilypond[quote,fragment,verbatim,relative=2]
522 \once \override Stem #'thickness = #4.0
527 The @code{\override} must be done before the object is
528 started. Therefore, when altering @emph{Spanner} objects, like slurs or
529 beams, the @code{\override} command must be executed at the moment when
530 the object is created. In this example,
533 @lilypond[quote,fragment,verbatim,relative=2]
534 \override Slur #'thickness = #3.0
536 \override Beam #'thickness = #0.6
541 the slur is fatter but the beam is not. This is because the command for
542 @code{Beam} comes after the Beam is started. Therefore it has no effect.
544 Analogous to @code{\unset}, the @code{\revert} command for a context
545 undoes an @code{\override} command; like with @code{\unset}, it only
546 affects settings that were made in the same context. In other words, the
547 @code{\revert} in the next example does not do anything.
550 \override Voice.Stem #'thickness = #4.0
551 \revert Staff.Stem #'thickness
559 Internals: @internalsref{OverrideProperty}, @internalsref{RevertProperty},
560 @internalsref{PropertySet}, @internalsref{Backend}, and
561 @internalsref{All layout objects}.
566 The back-end is not very strict in type-checking object properties.
567 Cyclic references in Scheme values for properties can cause hangs
571 @node Changing context default settings
572 @subsection Changing context default settings
574 The adjustments of the previous subsections (@ref{Changing context
575 properties on the fly}, @ref{Modifying context plug-ins}, and
576 @ref{Layout tunings within contexts}) can also be entered separately
577 from the music, in the @code{\layout} block,
586 \override Stem #'thickness = #4.0
587 \remove "Time_signature_engraver"
598 takes the existing definition for context @context{Staff} from the
599 identifier @code{\Staff}.
604 \override Stem #'thickness = #4.0
605 \remove "Time_signature_engraver"
609 affect all staves in the score.
611 Other contexts can be modified analogously.
613 The @code{\set} keyword is optional within the @code{\layout} block, so
629 It is not possible to collect context changes in a variable, and apply
630 them to one @code{\context} definition by referring to that variable.
632 The @code{\RemoveEmptyStaffContext} will override your current
633 @code{\Staff} variable. If you wish to change the defaults for a
634 staff that uses @code{\RemoveEmptyStaffContext}, you must do so
635 after calling @code{\RemoveemptyStaffContext}, ie
640 \RemoveEmptyStaffContext
642 \override Stem #'thickness = #4.0
648 @node Defining new contexts
649 @subsection Defining new contexts
651 Specific contexts, like @context{Staff} and @code{Voice}, are made of
652 simple building blocks, and it is possible to compose engraver
653 plug-ins in different combinations, thereby creating new types of
656 The next example shows how to build a different type of
657 @context{Voice} context from scratch. It will be similar to
658 @code{Voice}, but prints centered slash noteheads only. It can be used
659 to indicate improvisation in Jazz pieces,
661 @lilypond[quote,raggedright]
664 \type "Engraver_group"
665 \consists "Note_heads_engraver"
666 \consists "Text_engraver"
667 \consists Pitch_squash_engraver
668 squashedPosition = #0
669 \override NoteHead #'style = #'slash
670 \override Stem #'transparent = ##t
674 \accepts "ImproVoice"
678 a4 d8 bes8 \new ImproVoice { c4^"ad lib" c
679 c4 c^"undress" c_"while playing :)" c }
685 These settings are again done within a @code{\context} block inside a
686 @code{\layout} block,
696 In the following discussion, the example input shown should go on the
697 @dots{} in the previous fragment.
699 First, the context gets a name. Instead of @context{Voice} it
700 will be called @context{ImproVoice},
706 Since it is similar to the @context{Voice}, we want commands that work
707 on (existing) @context{Voice}s to remain working. This is achieved by
708 giving the new context an alias @context{Voice},
714 The context will print notes, and instructive texts
717 \consists Note_heads_engraver
718 \consists Text_engraver
721 but only on the center line,
724 \consists Pitch_squash_engraver
725 squashedPosition = #0
728 The @internalsref{Pitch_squash_engraver} modifies note heads (created
729 by @internalsref{Note_heads_engraver}) and sets their vertical
730 position to the value of @code{squashedPosition}, in this case@tie{}@code{0},
733 The notes look like a slash, without a stem,
736 \override NoteHead #'style = #'slash
737 \override Stem #'transparent = ##t
741 All these plug-ins have to cooperate, and this is achieved with a
742 special plug-in, which must be marked with the keyword @code{\type}.
743 This should always be @internalsref{Engraver_group},
746 \type "Engraver_group"
754 \type "Engraver_group"
755 \consists "Note_heads_engraver"
756 \consists "Text_engraver"
757 \consists Pitch_squash_engraver
758 squashedPosition = #0
759 \override NoteHead #'style = #'slash
760 \override Stem #'transparent = ##t
765 Contexts form hierarchies. We want to hang the @context{ImproVoice}
766 under @context{Staff}, just like normal @code{Voice}s. Therefore, we
767 modify the @code{Staff} definition with the @code{\accepts}
768 command,@footnote{The opposite of @code{\accepts} is @code{\denies},
769 which is sometimes needed when reusing existing context definitions.}
780 Putting both into a @code{\layout} block, like
790 \accepts "ImproVoice"
795 Then the output at the start of this subsection can be entered as
803 c c_"while playing :)"
812 @node The \override command
813 @section The \override command
815 In the previous section, we have already touched on a command that
816 changes layout details: the @code{\override} command. In this section,
817 we will look in more detail at how to use the command in practice.
818 First, we will give a few versatile commands that are sufficient
819 for many situations. The next section will discuss the general use of
825 * Constructing a tweak::
826 * Navigating the program reference::
827 * Layout interfaces::
828 * Determining the grob property::
835 @subsection Common tweaks
837 @c Should we point at ly/property-init.ly ? -gp
838 Some overrides are so common that predefined commands are provided as
839 short-cuts, for example, @code{\slurUp} and @code{\stemDown}. These
840 commands are described in
844 @c @ref{Notation manual},
847 under the sections for slurs and stems
850 The exact tuning possibilities for each type of layout object are
851 documented in the program reference of the respective
852 object. However, many layout objects share properties, which can be
853 used to apply generic tweaks. We mention a few of these:
856 @item The @code{extra-offset} property, which
857 @cindex @code{extra-offset}
858 has a pair of numbers as value, moves objects around in the printout.
859 The first number controls left-right movement; a positive number will
860 move the object to the right. The second number controls up-down
861 movement; a positive number will move it higher. The units of these
862 offsets are staff-spaces. The @code{extra-offset} property is a
863 low-level feature: the formatting engine is completely oblivious to
866 In the following example, the second fingering is moved a little to
867 the left, and 1.8 staff space downwards:
869 @cindex setting object properties
871 @lilypond[quote,fragment,relative=1,verbatim]
874 \once \override Fingering
875 #'extra-offset = #'(-0.3 . -1.8)
880 Setting the @code{transparent} property will cause an object to be printed
881 in `invisible ink': the object is not printed, but all its other
882 behavior is retained. The object still takes up space, it takes part in
883 collisions, and slurs, ties, and beams can be attached to it.
885 @cindex transparent objects
886 @cindex removing objects
887 @cindex hiding objects
888 @cindex invisible objects
889 The following example demonstrates how to connect different voices
890 using ties. Normally, ties only connect two notes in the same
891 voice. By introducing a tie in a different voice,
893 @lilypond[quote,fragment,relative=2]
902 and blanking the first up-stem in that voice, the tie appears to cross
905 @lilypond[quote,fragment,relative=2,verbatim]
907 \once \override Stem #'transparent = ##t
915 The @code{padding} property for objects with
916 @cindex @code{padding}
917 @code{side-position-interface} can be set to increase the distance between
918 symbols that are printed above or below notes. We provide two
919 examples; a more elaborate explanation is in @ref{Constructing a
922 @lilypond[quote,fragment,relative=1,verbatim]
924 \override Script #'padding = #3
928 @lilypond[quote,fragment,relative=1,verbatim]
929 % This will not work, see below:
930 \override MetronomeMark #'padding = #3
934 \override Score.MetronomeMark #'padding = #3
939 Note in the second example how important it is to figure out what
940 context handles a certain object. Since the @code{MetronomeMark} object
941 is handled in the Score context, property changes in the @code{Voice}
942 context will not be noticed.
946 More specific overrides are also possible. The next section
947 discusses in depth how to figure out these statements for yourself.
950 @node Constructing a tweak
951 @subsection Constructing a tweak
953 The general procedure of changing output, that is, entering
957 \override Voice.Stem #'thickness = #3.0
961 means that we have to determine these bits of information:
964 @item the context: here @context{Voice}.
965 @item the layout object: here @code{Stem}.
966 @item the layout property: here @code{thickness}
967 @item a sensible value: here @code{3.0}
971 @cindex internal documentation
972 @cindex finding graphical objects
973 @cindex graphical object descriptions
975 @cindex @code{\override}
976 @cindex internal documentation
978 We demonstrate how to glean this information from the notation manual
979 and the program reference.
981 @node Navigating the program reference
982 @subsection Navigating the program reference
984 Suppose we want to move the fingering indication in the fragment
987 @lilypond[quote,fragment,relative=2,verbatim]
993 If you visit the documentation on fingering instructions (in
994 @ref{Fingering instructions}), you will notice that there is written:
999 Program reference: @internalsref{FingerEvent} and @internalsref{Fingering}.
1005 This fragment points to two parts of the program reference: a page
1006 on @code{FingerEvent} and one on @code{Fingering}.
1008 The page on @code{FingerEvent} describes the properties of the music
1009 expression for the input @code{-2}. The page contains many links
1010 forward. For example, it says
1013 Accepted by: @internalsref{Fingering_engraver},
1017 That link brings us to the documentation for the Engraver, the
1021 This engraver creates the following layout objects: @internalsref{Fingering}.
1024 In other words, once the @code{FingerEvent}s are interpreted, the
1025 @code{Fingering_engraver} plug-in will process them.
1026 The @code{Fingering_engraver} is also listed to create
1027 @internalsref{Fingering} objects,
1030 Lo and behold, that is also the
1031 second bit of information listed under @b{See also} in the Notation
1032 manual. By clicking around in the program reference, we can follow the
1033 flow of information within the program, either forward (like we did
1034 here), or backwards, following links like this:
1038 @item @internalsref{Fingering}:
1039 @internalsref{Fingering} objects are created by:
1040 @b{@internalsref{Fingering_engraver}}
1042 @item @internalsref{Fingering_engraver}:
1043 Music types accepted: @b{@internalsref{fingering-event}}
1045 @item @internalsref{fingering-event}:
1046 Music event type @code{fingering-event} is in Music expressions named
1047 @b{@internalsref{FingerEvent}}
1050 This path goes against the flow of information in the program: it
1051 starts from the output, and ends at the input event.
1053 The program reference can also be browsed like a normal document. It
1054 contains a chapter on
1056 @internalsref{Music definitions},
1059 @code{Music definitions}
1061 on @internalsref{Translation}, and the @internalsref{Backend}. Every
1062 chapter lists all the definitions used, and all properties that may be
1066 @node Layout interfaces
1067 @subsection Layout interfaces
1069 @cindex interface, layout
1070 @cindex layout interface
1073 The HTML page that we found in the previous section, describes the
1074 layout object called @internalsref{Fingering}. Such an object is a
1075 symbol within the score. It has properties that store numbers (like
1076 thicknesses and directions), but also pointers to related objects. A
1077 layout object is also called a @emph{Grob}, which is short for Graphical
1078 Object. For more details about Grobs, see @internalsref{grob-interface}.
1080 The page for @code{Fingering} lists the definitions for the
1081 @code{Fingering} object. For example, the page says
1084 @code{padding} (dimension, in staff space):
1090 which means that the number will be kept at a distance of at least 0.6
1094 Each layout object may have several functions as a notational or
1095 typographical element. For example, the Fingering object
1096 has the following aspects
1100 Its size is independent of the horizontal spacing, unlike slurs or beams.
1103 It is a piece of text. Granted, it is usually a very short text.
1106 That piece of text is typeset with a font, unlike slurs or beams.
1109 Horizontally, the center of the symbol should be aligned to the
1110 center of the notehead.
1113 Vertically, the symbol is placed next to the note and the staff.
1116 The vertical position is also coordinated with other super- and subscript
1120 Each of these aspects is captured in so-called @emph{interface}s,
1121 which are listed on the @internalsref{Fingering} page at the bottom
1124 This object supports the following interfaces:
1125 @internalsref{item-interface},
1126 @internalsref{self-alignment-interface},
1127 @internalsref{side-position-interface}, @internalsref{text-interface},
1128 @internalsref{text-script-interface}, @internalsref{font-interface},
1129 @internalsref{finger-interface}, and @internalsref{grob-interface}.
1132 Clicking any of the links will take you to the page of the respective
1133 object interface. Each interface has a number of properties. Some of
1134 them are not user-serviceable (``Internal properties''), but others
1137 We have been talking of @emph{the} @code{Fingering} object, but actually it
1138 does not amount to much. The initialization file
1139 @file{scm/@/define@/-grobs@/.scm} shows the soul of the `object',
1144 (avoid-slur . around)
1145 (slur-padding . 0.2)
1146 (staff-padding . 0.5)
1147 (self-alignment-X . 0)
1148 (self-alignment-Y . 0)
1149 (script-priority . 100)
1150 (callbacks . ((stencil . ,Text_interface::print)
1151 (direction . ,Script_interface::calc_direction)))
1152 (font-encoding . fetaNumber)
1153 (font-size . -5) ; don't overlap when next to heads.
1154 (meta . ((class . Item)
1155 (interfaces . (finger-interface
1157 text-script-interface
1159 side-position-interface
1160 self-alignment-interface
1161 item-interface))))))
1165 As you can see, the @code{Fingering} object is nothing more than a
1166 bunch of variable settings, and the webpage in the Program Reference
1167 is directly generated from this definition.
1169 @node Determining the grob property
1170 @subsection Determining the grob property
1173 Recall that we wanted to change the position of the @b{2} in
1175 @lilypond[quote,fragment,relative=2,verbatim]
1181 Since the @b{2} is vertically positioned next to its note, we have to
1182 meddle with the interface associated with this positioning. This is
1183 done using @code{side-position-interface}. The page for this interface
1187 @code{side-position-interface}
1189 Position a victim object (this one) next to other objects (the
1190 support). The property @code{direction} signifies where to put the
1191 victim object relative to the support (left or right, up or down?)
1196 below this description, the variable @code{padding} is described as
1201 (dimension, in staff space)
1203 Add this much extra space between objects that are next to each other.
1207 By increasing the value of @code{padding}, we can move away the
1208 fingering. The following command inserts 3 staff spaces of white
1209 between the note and the fingering:
1211 \once \override Voice.Fingering #'padding = #3
1214 Inserting this command before the Fingering object is created,
1215 i.e., before @code{c2}, yields the following result:
1217 @lilypond[quote,relative=2,fragment,verbatim]
1218 \once \override Voice.Fingering #'padding = #3
1225 In this case, the context for this tweak is @context{Voice}. This
1226 fact can also be deduced from the program reference, for the page for
1227 the @internalsref{Fingering_engraver} plug-in says
1230 Fingering_engraver is part of contexts: @dots{} @b{@internalsref{Voice}}
1233 @node Difficult tweaks
1234 @subsection Difficult tweaks
1236 There are a few classes of difficult adjustments.
1239 First, when there are
1240 several of the same objects at one point, and you want to adjust only
1243 For example, if you want to change only one note head in a chord.
1245 In this case, the @code{\applyOutput} function must be used. The
1246 next example defines a Scheme function @code{set-position-font-size}
1247 that sets the @code{font-size} property, but only
1248 on objects that have @internalsref{note-head-interface} and are at the
1251 @lilypond[quote,verbatim]
1252 #(define ((set-position-font-size pos size) grob origin current)
1254 ((meta (ly:grob-property grob 'meta))
1255 (interfaces (cdr (assoc 'interfaces meta)))
1256 (position (ly:grob-property grob 'staff-position)))
1258 ; is this a note head?
1259 (memq 'note-head-interface interfaces)
1261 ; is the Y coordinate right?
1265 (set! (ly:grob-property grob 'font-size) size))))
1269 \applyOutput #(set-position-font-size -2 4)
1275 A similar technique can be used for accidentals. In that case, the
1276 function should check for @code{accidental-interface}.
1279 Another difficult adjustment is the appearance of spanner objects,
1280 such as slur and tie. Initially, only one of these objects is created,
1281 and they can be adjusted with the normal mechanism. However, in some
1282 cases the spanners cross line breaks. If this happens, these objects
1283 are cloned. A separate object is created for every system that it is
1284 in. These are clones of the original object and inherit all
1285 properties, including @code{\override}s.
1288 In other words, an @code{\override} always affects all pieces of a
1289 broken spanner. To change only one part of a spanner at a line break,
1290 it is necessary to hook into the formatting process. The
1291 @code{after-line-breaking} callback contains the Scheme procedure that
1292 is called after the line breaks have been determined, and layout
1293 objects have been split over different systems.
1295 In the following example, we define a procedure
1296 @code{my-callback}. This procedure
1300 determines if we have been split across line breaks
1302 if yes, retrieves all the split objects
1304 checks if we are the last of the split objects
1306 if yes, it sets @code{extra-offset}.
1309 This procedure is installed into @internalsref{Tie}, so the last part
1310 of the broken tie is translated up.
1312 @lilypond[quote,verbatim,raggedright]
1313 #(define (my-callback grob)
1315 ; have we been split?
1316 (orig (ly:grob-original grob))
1318 ; if yes, get the split pieces (our siblings)
1319 (siblings (if (ly:grob? orig)
1320 (ly:spanner-broken-into orig) '() )))
1322 (if (and (>= (length siblings) 2)
1323 (eq? (car (last-pair siblings)) grob))
1324 (ly:grob-set-property! grob 'extra-offset '(-2 . 5)))))
1327 \override Tie #'after-line-breaking =
1334 When applying this trick, the new @code{after-line-breaking} callback
1335 should also call the old one @code{after-line-breaking}, if there is
1336 one. For example, if using this with @code{Hairpin},
1337 @code{Hairpin::after_line_breaking} should also be called.
1340 @item Some objects cannot be changed with @code{\override} for
1341 technical reasons. Examples of those are @code{NonMusicalPaperColumn}
1342 and @code{PaperColumn}. They can be changed with the
1343 @code{\outputProperty} function, which works similar to @code{\once
1344 \override}, but uses a different syntax,
1348 #"Score.NonMusicalPaperColumn" % Grob name
1349 #'line-break-system-details % Property name
1350 #'((next-padding . 20)) % Value