1 @c -*- coding: utf-8; mode: texinfo; -*-
2 @c This file is part of lilypond.tely
4 Translation of GIT committish: FILL-IN-HEAD-COMMITTISH
6 When revising a translation, copy the HEAD committish of the
7 version that you are working on. See TRANSLATION for details.
10 @node Changing defaults
11 @chapter Changing defaults
14 The purpose of LilyPond's design is to provide the finest output
15 quality as a default. Nevertheless, it may happen that you need to
16 change this default layout. The layout is controlled through a large
17 number of proverbial @q{knobs and switches.} This chapter does not
18 list each and every knob. Rather, it outlines what groups of controls
19 are available and explains how to lookup which knob to use for a
23 @cindex Program reference
25 The controls available for tuning are described in a separate
28 Program reference manual.
31 @ref{Top,Program reference,,lilypond-internals}.
34 lists all different variables, functions and options available in
35 LilyPond. It is written as a HTML document, which is available
36 @c leave the @uref as one long line.
37 @uref{http://@/lilypond@/.org/@/doc/@/stable/@/Documentation/@/user/@/lilypond@/-internals/,on@/-line},
38 but is also included with the LilyPond documentation package.
40 There are four areas where the default settings may be changed:
44 Automatic notation: changing the automatic creation of notation
45 elements. For example, changing the beaming rules.
48 Output: changing the appearance of individual
49 objects. For example, changing stem directions or the location of
53 Context: changing aspects of the translation from music events to
54 notation. For example, giving each staff a separate time signature.
57 Page layout: changing the appearance of the spacing, line
58 breaks, and page dimensions. These modifications are discussed
59 in @ref{Non-musical notation}, and @ref{Spacing issues}.
62 Internally, LilyPond uses Scheme (a LISP dialect) to provide
63 infrastructure. Overriding layout decisions in effect accesses the
64 program internals, which requires Scheme input. Scheme elements are
65 introduced in a @code{.ly} file with the hash mark
66 @code{#}.@footnote{@ref{Scheme tutorial}, contains a short tutorial
67 on entering numbers, lists, strings, and symbols in Scheme.}
71 * Automatic notation::
72 * Interpretation contexts::
73 * The \override command::
77 @node Automatic notation
78 @section Automatic notation
80 This section describes how to change the way that accidentals and
81 beams are automatically displayed.
84 * Automatic accidentals::
85 * Setting automatic beam behavior::
88 @node Automatic accidentals
89 @subsection Automatic accidentals
90 @cindex Automatic accidentals
92 Common rules for typesetting accidentals have been placed in a
93 function. This function is called as follows
95 @funindex set-accidental-style
97 #(set-accidental-style 'STYLE)
100 @c TODO: check the context stuff below
101 @c -does it *really* work?
102 @c -the default contexts as specified in
103 @c scm/music-function.scm seem to be different -vv
105 Optionally, the function can take two arguments: the name of the
106 accidental style, and an optional argument that denotes the context that
110 #(set-accidental-style 'STYLE #('CONTEXT#))
113 If no context name is supplied, @code{Staff} is the default,
114 but you may wish to apply the accidental style to a single @code{Voice}
117 The following accidental styles are supported:
121 This is the default typesetting behavior. It corresponds
122 to 18th century common practice: Accidentals are
123 remembered to the end of the measure in which they occur and
124 only on their own octave.
126 @lilypond[quote,ragged-right]
127 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
128 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
130 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
131 \change Staff = up cis' \change Staff = down <fis, a>
132 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
137 << \context Staff = "up" {
138 %#(set-accidental-style 'default)
140 \context Staff = "down"{
141 %#(set-accidental-style 'default)
143 \header { piece = \markup {\fill-line { \fontsize #3 "'default" }}}
148 The normal behavior is to remember the accidentals on
149 Staff-level. This variable, however, typesets accidentals
150 individually for each voice. Apart from that, the rule is similar to
155 #(set-accidental-style 'voice)
160 As a result, accidentals from one voice do not get canceled in other
161 voices, which is often an unwanted result: in the following example, it
162 is hard to determine whether the second @samp{a} should be played
165 @lilypond[quote,ragged-right]
166 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
167 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
169 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
170 \change Staff = up cis' \change Staff = down <fis, a>
171 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
176 << \context Staff = "up" {
177 #(set-accidental-style 'voice)
179 \context Staff = "down"{
180 #(set-accidental-style 'voice)
182 \header { piece = \markup {\fill-line { \fontsize #3 "'voice" }}}
186 The @code{voice} option should be used if the voices
187 are to be read solely by individual musicians. If the staff is to be
188 used by one musician (e.g., a conductor) then
189 @code{modern} or @code{modern-cautionary}
190 should be used instead.
193 @funindex modern style accidentals
194 This rule corresponds to the common practice in the 20th century. This rule
195 prints the same accidentals as @code{default}, but temporary
196 accidentals also are canceled in other octaves. Furthermore,
197 in the same octave, they also get canceled in the following
198 measure: in the following example, notice the two natural signs which appear
199 in the second bar of the upper staff.
201 @lilypond[quote,ragged-right]
202 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
203 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
205 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
206 \change Staff = up cis' \change Staff = down <fis, a>
207 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
212 << \context Staff = "up" {
213 #(set-accidental-style 'modern)
215 \context Staff = "down"{
216 #(set-accidental-style 'modern)
218 \header { piece = \markup {\fill-line { \fontsize #3 "'modern" }}}
222 @item @code{modern-cautionary}
223 @funindex modern-cautionary
224 This rule is similar to @code{modern}, but the @q{extra} accidentals
225 (the ones not typeset by @code{default}) are typeset as cautionary
226 accidentals. They are printed in reduced size or (by default)
227 with parentheses -- this can be set by definig the @code{cautionary-style}
228 property of the @internalsref{AccidentalSuggestion} object.
230 @lilypond[quote,ragged-right]
231 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
232 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
234 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
235 \change Staff = up cis' \change Staff = down <fis, a>
236 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
241 << \context Staff = "up" {
242 #(set-accidental-style 'modern-cautionary)
244 \context Staff = "down"{
245 #(set-accidental-style 'modern-cautionary)
247 \header { piece = \markup {\fill-line { \fontsize #3 "'modern-cautionary" }}}
251 @funindex modern-voice
253 This rule is used for multivoice accidentals to be read both by musicians
254 playing one voice and musicians playing all voices. Accidentals are
255 typeset for each voice, but they @emph{are} canceled across voices in
256 the same @internalsref{Staff}.
258 @lilypond[quote,ragged-right]
259 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
260 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
262 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
263 \change Staff = up cis' \change Staff = down <fis, a>
264 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
269 << \context Staff = "up" {
270 #(set-accidental-style 'modern-voice)
272 \context Staff = "down"{
273 #(set-accidental-style 'modern-voice)
275 \header { piece = \markup {\fill-line { \fontsize #3 "'modern-voice" }}}
279 @funindex modern-voice-cautionary
280 @item modern-voice-cautionary
281 This rule is the same as @code{modern-voice}, but with the extra
282 accidentals (the ones not typeset by @code{voice}) typeset
283 as cautionaries. Even though all accidentals typeset by
284 @code{default} @emph{are} typeset by this variable,
285 some of them are typeset as cautionaries.
287 @lilypond[quote,ragged-right]
288 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
289 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
291 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
292 \change Staff = up cis' \change Staff = down <fis, a>
293 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
298 << \context Staff = "up" {
299 #(set-accidental-style 'modern-voice-cautionary)
301 \context Staff = "down"{
302 #(set-accidental-style 'modern-voice-cautionary)
304 \header { piece = \markup {\fill-line { \fontsize #3 "'modern-voice-cautionary" }}}
309 @funindex piano accidentals
310 This accidental style takes place in a GrandStaff context. However, you have to
311 explicitly set it for @emph{each} individual Staff of the GrandStaff:
314 \new GrandStaff @{ <<
315 \new Staff = "up" @{ <<
316 #(set-accidental-style 'piano)
319 \new Staff = "down"@{ <<
320 #(set-accidental-style 'piano)
326 This rule reflects 20th century practice for piano notation. Its behavior is very
327 similar to @code{modern} style, but here accidentals also get canceled
328 across the staves in the same @internalsref{GrandStaff} or
329 @internalsref{PianoStaff}.
331 @lilypond[quote,ragged-right]
332 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
333 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
335 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
336 \change Staff = up cis' \change Staff = down <fis, a>
337 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
342 << \context Staff = "up" {
343 #(set-accidental-style 'piano)
345 \context Staff = "down"{
346 #(set-accidental-style 'piano)
348 \header { piece = \markup {\fill-line { \fontsize #3 "'piano" }}}
352 @item piano-cautionary
353 @funindex #(set-accidental-style 'piano-cautionary)
354 Same as @code{#(set-accidental-style 'piano)} but with the extra
355 accidentals typeset as cautionaries.
357 @lilypond[quote,ragged-right]
358 musicA = { << \relative { cis'8 fis, d'4 <a cis>8 f bis4 | cis2. <c, g'>4 | } \\
359 \relative { ais'2 cis, | fis8 b a4 cis2 | } >> }
361 musicB = { \clef bass \new Voice { \voiceTwo \relative { < fis, a cis>4
362 \change Staff = up cis' \change Staff = down <fis, a>
363 \change Staff = up dis' | \change Staff = down <fis, a cis>4 gis
368 << \context Staff = "up" {
369 #(set-accidental-style 'piano-cautionary)
371 \context Staff = "down"{
372 #(set-accidental-style 'piano-cautionary)
374 \header { piece = \markup {\fill-line { \fontsize #3 "'piano-cautionary" }}}
379 @funindex no-reset accidental style
380 This is the same as @code{default} but with accidentals lasting
381 @q{forever} and not only until the next measure
382 @lilypond[quote,ragged-right,verbatim,relative=1]
383 #(set-accidental-style 'no-reset)
388 This is sort of the opposite of @code{no-reset}: Accidentals
389 are not remembered at all -- and hence all accidentals are
390 typeset relative to the key signature, regardless of what was
393 @lilypond[quote,ragged-right,verbatim,relative=1]
394 #(set-accidental-style 'forget)
395 \key d\major c4 c cis cis d d dis dis
402 Program reference: @internalsref{Accidental_engraver},
403 @internalsref{Accidental}, @internalsref{AccidentalSuggestion} and @internalsref{AccidentalPlacement}.
408 Simultaneous notes are considered to be entered in sequential
409 mode. This means that in a chord the accidentals are typeset as if the
410 notes in the chord happen one at a time, in the order in which
411 they appear in the input file. This is a problem when accidentals
412 in a chord depend on each other,
413 which does not happen for the default accidental style. The problem
414 can be solved by manually inserting @code{!} and @code{?} for the
418 @node Setting automatic beam behavior
419 @subsection Setting automatic beam behavior
421 @funindex autoBeamSettings
422 @funindex (end * * * *)
423 @funindex (begin * * * *)
424 @cindex automatic beams, tuning
425 @cindex tuning automatic beaming
427 @c [TODO: use \applyContext]
429 In normal time signatures, automatic beams can start on any note but can
430 only end in a few positions within the measure: beams can end on a beat,
431 or at durations specified by the properties in
432 @code{autoBeamSettings}. The properties in @code{autoBeamSettings}
433 consist of a list of rules for where beams can begin and end. The
434 default @code{autoBeamSettings} rules are defined in
435 @file{scm/@/auto@/-beam@/.scm}.
437 In order to add a rule to the list, use
439 #(override-auto-beam-setting '(be p q n m) a b [context])
444 @item @code{be} is either "begin" or "end".
446 @item @code{p/q} is the duration of the note for which you want
447 to add a rule. A beam is considered to have the duration of its
448 shortest note. Set @code{p} and @code{q} to @code{'*'} to
449 have this apply to any beam.
451 @item @code{n/m} is the time signature to which
452 this rule should apply. Set @code{n} and @code{m} to @code{'*'}
453 to have this apply in any time signature.
455 @item @code{a/b} is the position in the bar at which the beam should
458 @item @code{context} is optional, and it specifies the context at which
459 the change should be made. The default is @code{'Voice}.
460 @code{#(score-override-auto-beam-setting '(A B C D) E F)} is equivalent to
461 @code{#(override-auto-beam-setting '(A B C D) E F 'Score)}.
465 For example, if automatic beams should always end on the first quarter
469 #(override-auto-beam-setting '(end * * * *) 1 4)
472 You can force the beam settings to only take effect on beams whose shortest
473 note is a certain duration
475 @lilypond[quote,fragment,ragged-right,verbatim,relative=2]
477 #(override-auto-beam-setting '(end 1 16 * *) 1 16)
479 a32 a a a a16 a a a a a |
480 #(override-auto-beam-setting '(end 1 32 * *) 1 16)
481 a32 a a a a16 a a a a a |
484 You can force the beam settings to only take effect in certain time
487 @lilypond[quote,fragment,ragged-right,verbatim,relative=2]
489 #(override-auto-beam-setting '(end * * 5 8) 2 8)
497 You can also remove a previously set beam-ending rule by using
500 #(revert-auto-beam-setting '(be p q n m) a b [context])
504 be, p, q, n, m, a, b and context are the same as above. Note that the
505 default rules are specified in @file{scm/@/auto@/-beam@/.scm},
506 so you can revert rules that you did not explicitly create.
508 @lilypond[quote,fragment,ragged-right,verbatim,relative=2]
510 a16 a a a a a a a a a a a a a a a
511 #(revert-auto-beam-setting '(end 1 16 4 4) 1 4)
512 a16 a a a a a a a a a a a a a a a
515 The rule in a revert-auto-beam-setting statement must exactly match the
516 original rule. That is, no wildcard expansion is taken into account.
518 @lilypond[quote,fragment,ragged-right,verbatim,relative=2]
520 #(override-auto-beam-setting '(end 1 16 1 4) 1 8)
522 #(revert-auto-beam-setting '(end 1 16 * *) 1 8) % this won't revert it!
524 #(revert-auto-beam-setting '(end 1 16 1 4) 1 8) % this will
530 @c TODO: old material -- not covered by above stuff, I think.
531 If automatic beams should end on every quarter in 5/4 time, specify
534 #(override-auto-beam-setting '(end * * * *) 1 4 'Staff)
535 #(override-auto-beam-setting '(end * * * *) 1 2 'Staff)
536 #(override-auto-beam-setting '(end * * * *) 3 4 'Staff)
537 #(override-auto-beam-setting '(end * * * *) 5 4 'Staff)
541 The same syntax can be used to specify beam starting points. In this
542 example, automatic beams can only end on a dotted quarter note
544 #(override-auto-beam-setting '(end * * * *) 3 8)
545 #(override-auto-beam-setting '(end * * * *) 1 2)
546 #(override-auto-beam-setting '(end * * * *) 7 8)
548 In 4/4 time signature, this means that automatic beams could end only on
549 3/8 and on the fourth beat of the measure (after 3/4, that is 2 times
550 3/8, has passed within the measure).
552 If any unexpected beam behaviour occurs, check the default automatic beam
553 settings in @file{scm/@/auto@/-beam@/.scm}
554 for possible interference, because the beam
555 endings defined there will still apply on top of your own overrides. Any
556 unwanted endings in the default vales must be reverted for your time
559 For example, to typeset @code{(3 4 3 2)}-beam endings in 12/8, begin
563 %%% revert default values in scm/auto-beam.scm regarding 12/8 time
564 #(revert-auto-beam-setting '(end * * 12 8) 3 8)
565 #(revert-auto-beam-setting '(end * * 12 8) 3 4)
566 #(revert-auto-beam-setting '(end * * 12 8) 9 8)
569 #(override-auto-beam-setting '(end 1 8 12 8) 3 8)
570 #(override-auto-beam-setting '(end 1 8 12 8) 7 8)
571 #(override-auto-beam-setting '(end 1 8 12 8) 10 8)
574 @cindex automatic beam generation
576 @funindex autoBeaming
579 If beams are used to indicate melismata in songs, then automatic
580 beaming should be switched off with @code{\autoBeamOff}.
585 @funindex \autoBeamOff
587 @funindex \autoBeamOn
592 Beaming patterns may be altered with the @code{beatGrouping} property,
594 @lilypond[quote,verbatim,relative=2,fragment,ragged-right]
596 \set beatGrouping = #'(2 3)
598 \set beatGrouping = #'(3 2)
605 If a score ends while an automatic beam has not been ended and is
606 still accepting notes, this last beam will not be typeset at all. The
607 same holds polyphonic voices, entered with @code{<< @dots{} \\ @dots{}
608 >>}. If a polyphonic voice ends while an automatic beam is still
609 accepting notes, it is not typeset.
612 @node Interpretation contexts
613 @section Interpretation contexts
615 This section describes what contexts are, and how to modify them.
618 * Contexts explained::
619 * Creating contexts::
620 * Changing context properties on the fly::
621 * Modifying context plug-ins::
622 * Layout tunings within contexts::
623 * Changing context default settings::
624 * Defining new contexts::
625 * Aligning contexts::
626 * Vertical grouping of grobs::
630 @node Contexts explained
631 @subsection Contexts explained
633 When music is printed, a lot of notational elements must be added to the
634 output. For example, compare the input and output of the following example:
636 @lilypond[quote,verbatim,relative=2,fragment]
640 The input is rather sparse, but in the output, bar lines, accidentals,
641 clef, and time signature are added. LilyPond @emph{interprets} the
642 input. During this step, the musical information is inspected in time
643 order, similar to reading a score from left to right. While reading
644 the input, the program remembers where measure boundaries are, and which
645 pitches require explicit accidentals. This information can be presented on
646 several levels. For example, the effect of an accidental is limited
647 to a single staff, while a bar line must be synchronized across the
650 Within LilyPond, these rules and bits of information are grouped in
651 @emph{Contexts}. Some examples of contexts are @context{Voice},
652 @context{Staff}, and @context{Score}. They are hierarchical, for
653 example: a @context{Staff} can contain many @context{Voice}s, and a
654 @context{Score} can contain many @context{Staff} contexts.
657 @image{context-example,5cm,,}
660 Each context has the responsibility for enforcing some notation rules,
661 creating some notation objects and maintaining the associated
662 properties. For example, the @context{Voice} context may introduce an
663 accidental and then the @context{Staff} context maintains the rule to
664 show or suppress the accidental for the remainder of the measure. The
665 synchronization of bar lines is handled at @context{Score} context.
667 However, in some music we may not want the bar lines to be
668 synchronized -- consider a polymetric score in 4/4 and 3/4 time. In
669 such cases, we must modify the default settings of the @context{Score}
670 and @context{Staff} contexts.
672 For very simple scores, contexts are created implicitly, and you need
673 not be aware of them. For larger pieces, such as anything with more
674 than one staff, they must be
675 created explicitly to make sure that you get as many staves as you
676 need, and that they are in the correct order. For typesetting pieces
677 with specialized notation, it can be useful to modify existing or
678 to define new contexts.
681 A complete description of all available contexts is in the program
684 @internalsref{Contexts}.
687 Translation @arrow{} Context.
690 @c [TODO: describe propagation]
693 @node Creating contexts
694 @subsection Creating contexts
696 For scores with only one voice and one staff, contexts are
697 created automatically. For more complex scores, it is necessary to
698 create them by hand. There are three commands that do this.
703 The easiest command is @code{\new}, and it also the quickest to type.
704 It is prepended to a music expression, for example
708 @cindex Context, creating
711 \new @var{type} @var{music expression}
715 where @var{type} is a context name (like @code{Staff} or
716 @code{Voice}). This command creates a new context, and starts
717 interpreting the @var{music expression} with that.
719 A practical application of @code{\new} is a score with many
720 staves. Each part that should be on its own staff, is preceded with
723 @lilypond[quote,verbatim,relative=2,ragged-right,fragment]
730 The @code{\new} command may also give a name to the context,
733 \new @var{type} = @var{id} @var{music}
735 However, this user specified name is only used if there is no other
736 context already earlier with the same name.
742 Like @code{\new}, the @code{\context} command also directs a music
743 expression to a context object, but gives the context an explicit name. The
747 \context @var{type} = @var{id} @var{music}
750 This form will search for an existing context of type @var{type}
751 called @var{id}. If that context does not exist yet, a new
752 context with the specified name is created. This is useful if
753 the context is referred to later on. For example, when
754 setting lyrics the melody is in a named context
757 \context Voice = "@b{tenor}" @var{music}
761 so the texts can be properly aligned to its notes,
764 \new Lyrics \lyricsto "@b{tenor}" @var{lyrics}
769 Another possible use of named contexts is funneling two different
770 music expressions into one context. In the following example,
771 articulations and notes are entered separately,
775 arts = @{ s4-. s4-> @}
778 They are combined by sending both to the same @context{Voice} context,
782 \new Staff \context Voice = "A" \music
783 \context Voice = "A" \arts
786 @lilypond[quote,ragged-right]
790 \new Staff \context Voice = "A" \music
791 \context Voice = "A" \arts
795 With this mechanism, it is possible to define an Urtext (original
796 edition), with the option to put several distinct articulations on the
799 @cindex creating contexts
802 The third command for creating contexts is
804 \context @var{type} @var{music}
809 This is similar to @code{\context} with @code{= @var{id}}, but matches
810 any context of type @var{type}, regardless of its given name.
812 This variant is used with music expressions that can be interpreted at
813 several levels. For example, the @code{\applyOutput} command (see
814 @ref{Running a function on all layout objects}). Without an explicit
815 @code{\context}, it is usually applied to @context{Voice}
818 \applyOutput #'@var{context} #@var{function} % apply to Voice
821 To have it interpreted at the @context{Score} or @context{Staff} level use
825 \applyOutput #'Score #@var{function}
826 \applyOutput #'Staff #@var{function}
832 @node Changing context properties on the fly
833 @subsection Changing context properties on the fly
837 @cindex changing properties
839 Each context can have different @emph{properties}, variables contained
840 in that context. They can be changed during the interpretation step.
841 This is achieved by inserting the @code{\set} command in the music,
844 \set @var{context}.@var{prop} = #@var{value}
848 @lilypond[quote,verbatim,relative=2,fragment]
850 \set Score.skipBars = ##t
854 This command skips measures that have no notes. The result is that
855 multi-rests are condensed. The value assigned is a Scheme object. In
856 this case, it is @code{#t}, the boolean True value.
858 If the @var{context} argument is left out, then the current bottom-most
859 context (typically @context{ChordNames}, @context{Voice}, or
860 @context{Lyrics}) is used. In this example,
862 @lilypond[quote,verbatim,relative=2,fragment]
864 \set autoBeaming = ##f
869 the @var{context} argument to @code{\set} is left out, so automatic
870 beaming is switched off in the current @internalsref{Voice}. Note that
871 the bottom-most context does not always contain the property that you
872 wish to change -- for example, attempting to set the @code{skipBars}
873 property (of the bottom-most context, in this case @code{Voice}) will
876 @lilypond[quote,verbatim,relative=2,fragment]
882 Contexts are hierarchical, so if a bigger context was specified, for
883 example @context{Staff}, then the change would also apply to all
884 @context{Voice}s in the current stave. The change is applied
885 @q{on-the-fly}, during the music, so that the setting only affects the
886 second group of eighth notes.
890 There is also an @code{\unset} command,
892 \unset @var{context}.@var{prop}
896 which removes the definition of @var{prop}. This command removes
897 the definition only if it is set in @var{context}, so
900 \set Staff.autoBeaming = ##f
904 introduces a property setting at @code{Staff} level. The setting also
905 applies to the current @code{Voice}. However,
908 \unset Voice.autoBeaming
912 does not have any effect. To cancel this setting, the @code{\unset}
913 must be specified on the same level as the original @code{\set}. In
914 other words, undoing the effect of @code{Staff.autoBeaming = ##f}
917 \unset Staff.autoBeaming
920 Like @code{\set}, the @var{context} argument does not have to be
921 specified for a bottom context, so the two statements
924 \set Voice.autoBeaming = ##t
925 \set autoBeaming = ##t
933 Settings that should only apply to a single time-step can be entered
934 with @code{\once}, for example in
936 @lilypond[quote,verbatim,relative=2,fragment]
938 \once \set fontSize = #4.7
943 the property @code{fontSize} is unset automatically after the second
946 A full description of all available context properties is in the
947 program reference, see
949 @internalsref{Tunable context properties}.
952 Translation @arrow{} Tunable context properties.
956 @node Modifying context plug-ins
957 @subsection Modifying context plug-ins
959 Notation contexts (like @code{Score} and @code{Staff}) not only
961 they also contain plug-ins called @q{engravers} that create notation
962 elements. For example, the @code{Voice} context contains a
963 @code{Note_head_engraver} and the @code{Staff} context contains a
964 @code{Key_signature_engraver}.
966 For a full a description of each plug-in, see
968 @internalsref{Engravers}.
971 Program reference @arrow Translation @arrow{} Engravers.
973 Every context described in
975 @internalsref{Contexts}
978 Program reference @arrow Translation @arrow{} Context.
980 lists the engravers used for that context.
983 It can be useful to shuffle around these plug-ins. This is done by
984 starting a new context with @code{\new} or @code{\context}, and
990 \new @var{context} \with @{
1003 where the @dots{} should be the name of an engraver. Here is a simple
1004 example which removes @code{Time_signature_engraver} and
1005 @code{Clef_engraver} from a @code{Staff} context,
1007 @lilypond[quote,relative=1,verbatim,fragment]
1013 \remove "Time_signature_engraver"
1014 \remove "Clef_engraver"
1021 In the second staff there are no time signature or clef symbols. This
1022 is a rather crude method of making objects disappear since it will affect
1023 the entire staff. This method also influences the spacing, which may or
1024 may not be desirable. A more
1025 sophisticated method of blanking objects is shown in @ref{Common tweaks}.
1027 The next example shows a practical application. Bar lines and time
1028 signatures are normally synchronized across the score. This is done
1029 by the @code{Timing_translator} and @code{Default_bar_line_engraver}.
1030 This plug-in keeps an administration of time signature, location
1031 within the measure, etc. By moving thes engraver from @code{Score} to
1032 @code{Staff} context, we can have a score where each staff has its own
1035 @cindex polymetric scores
1036 @cindex Time signatures, multiple
1038 @lilypond[quote,relative=1,ragged-right,verbatim,fragment]
1040 \remove "Timing_translator"
1041 \remove "Default_bar_line_engraver"
1044 \consists "Timing_translator"
1045 \consists "Default_bar_line_engraver"
1051 \consists "Timing_translator"
1052 \consists "Default_bar_line_engraver"
1061 @node Layout tunings within contexts
1062 @subsection Layout tunings within contexts
1064 Each context is responsible for creating certain types of graphical
1065 objects. The settings used for printing these objects are also stored by
1066 context. By changing these settings, the appearance of objects can be
1069 The syntax for this is
1072 \override @var{context}.@var{name} #'@var{property} = #@var{value}
1075 Here @var{name} is the name of a graphical object, like @code{Stem} or
1076 @code{NoteHead}, and @var{property} is an internal variable of the
1077 formatting system (@q{grob property} or @q{layout property}). The latter is a
1078 symbol, so it must be quoted. The subsection @ref{Constructing a
1079 tweak}, explains what to fill in for @var{name}, @var{property}, and
1080 @var{value}. Here we only discuss the functionality of this command.
1085 \override Staff.Stem #'thickness = #4.0
1089 makes stems thicker (the default is 1.3, with staff line thickness as a
1090 unit). Since the command specifies @context{Staff} as context, it only
1091 applies to the current staff. Other staves will keep their normal
1092 appearance. Here we see the command in action:
1094 @lilypond[quote,verbatim,relative=2,fragment]
1096 \override Staff.Stem #'thickness = #4.0
1102 The @code{\override} command changes the definition of the @code{Stem}
1103 within the current @context{Staff}. After the command is interpreted
1104 all stems are thickened.
1106 Analogous to @code{\set}, the @var{context} argument may be left out,
1107 causing the default context @context{Voice} to be used. Adding
1108 @code{\once} applies the change during one timestep only.
1110 @lilypond[quote,fragment,verbatim,relative=2]
1112 \once \override Stem #'thickness = #4.0
1117 The @code{\override} must be done before the object is
1118 started. Therefore, when altering @emph{Spanner} objects such as slurs
1119 or beams, the @code{\override} command must be executed at the moment
1120 when the object is created. In this example,
1122 @lilypond[quote,fragment,verbatim,relative=2]
1123 \override Slur #'thickness = #3.0
1125 \override Beam #'thickness = #0.6
1130 the slur is fatter but the beam is not. This is because the command for
1131 @code{Beam} comes after the Beam is started, so it has no effect.
1133 Analogous to @code{\unset}, the @code{\revert} command for a context
1134 undoes an @code{\override} command; like with @code{\unset}, it only
1135 affects settings that were made in the same context. In other words, the
1136 @code{\revert} in the next example does not do anything.
1139 \override Voice.Stem #'thickness = #4.0
1140 \revert Staff.Stem #'thickness
1143 Some tweakable options are called @q{subproperties} and reside inside
1144 properties. To tweak those, use commands of the form
1146 @c leave this as a long long
1148 \override @var{context}.@var{name} #'@var{property} #'@var{subproperty} = #@var{value}
1155 \override Stem #'details #'beamed-lengths = #'(4 4 3)
1161 Internals: @internalsref{OverrideProperty}, @internalsref{RevertProperty},
1162 @internalsref{PropertySet}, @internalsref{Backend}, and
1163 @internalsref{All layout objects}.
1168 The back-end is not very strict in type-checking object properties.
1169 Cyclic references in Scheme values for properties can cause hangs
1170 or crashes, or both.
1173 @node Changing context default settings
1174 @subsection Changing context default settings
1176 The adjustments of the previous subsections (@ref{Changing context
1177 properties on the fly}, @ref{Modifying context plug-ins}, and
1178 @ref{Layout tunings within contexts}) can also be entered separately
1179 from the music in the @code{\layout} block,
1188 \override Stem #'thickness = #4.0
1189 \remove "Time_signature_engraver"
1194 The @code{\Staff} command brings in the existing definition of the
1195 staff context so that it can be modified.
1200 \override Stem #'thickness = #4.0
1201 \remove "Time_signature_engraver"
1205 affect all staves in the score. Other contexts can be modified
1208 The @code{\set} keyword is optional within the @code{\layout} block, so
1224 It is not possible to collect context changes in a variable and apply
1225 them to a @code{\context} definition by referring to that variable.
1227 The @code{\RemoveEmptyStaffContext} will overwrite your current
1228 @code{\Staff} settings. If you wish to change the defaults for a
1229 staff which uses @code{\RemoveEmptyStaffContext}, you must do so
1230 after calling @code{\RemoveemptyStaffContext}, ie
1235 \RemoveEmptyStaffContext
1237 \override Stem #'thickness = #4.0
1243 @node Defining new contexts
1244 @subsection Defining new contexts
1246 Specific contexts, like @context{Staff} and @code{Voice}, are made of
1247 simple building blocks. It is possible to create new types of
1248 contexts with different combinations of engraver plug-ins.
1250 The next example shows how to build a different type of
1251 @context{Voice} context from scratch. It will be similar to
1252 @code{Voice}, but only prints centered slash noteheads. It can be used
1253 to indicate improvisation in jazz pieces,
1255 @lilypond[quote,ragged-right]
1256 \layout { \context {
1258 \type "Engraver_group"
1259 \consists "Note_heads_engraver"
1260 \consists "Text_engraver"
1261 \consists Pitch_squash_engraver
1262 squashedPosition = #0
1263 \override NoteHead #'style = #'slash
1264 \override Stem #'transparent = ##t
1268 \accepts "ImproVoice"
1272 a4 d8 bes8 \new ImproVoice { c4^"ad lib" c
1273 c4 c^"undress" c_"while playing :)" c }
1279 These settings are defined within a @code{\context} block inside a
1280 @code{\layout} block,
1290 In the following discussion, the example input shown should go in place
1291 of the @dots{} in the previous fragment.
1293 First it is necessary to define a name for the new context:
1299 Since it is similar to the @context{Voice}, we want commands that work
1300 on (existing) @context{Voice}s to remain working. This is achieved by
1301 giving the new context an alias @context{Voice},
1307 The context will print notes and instructive texts, so we need to add
1308 the engravers which provide this functionality,
1311 \consists Note_heads_engraver
1312 \consists Text_engraver
1315 but we only need this on the center line,
1318 \consists Pitch_squash_engraver
1319 squashedPosition = #0
1322 The @internalsref{Pitch_squash_engraver} modifies note heads (created
1323 by @internalsref{Note_heads_engraver}) and sets their vertical
1324 position to the value of @code{squashedPosition}, in this case@tie{}@code{0},
1327 The notes look like a slash, and have no stem,
1330 \override NoteHead #'style = #'slash
1331 \override Stem #'transparent = ##t
1334 All these plug-ins have to cooperate, and this is achieved with a
1335 special plug-in, which must be marked with the keyword @code{\type}.
1336 This should always be @internalsref{Engraver_group},
1339 \type "Engraver_group"
1342 Put together, we get
1347 \type "Engraver_group"
1348 \consists "Note_heads_engraver"
1349 \consists "Text_engraver"
1350 \consists Pitch_squash_engraver
1351 squashedPosition = #0
1352 \override NoteHead #'style = #'slash
1353 \override Stem #'transparent = ##t
1359 Contexts form hierarchies. We want to hang the @context{ImproVoice}
1360 under @context{Staff}, just like normal @code{Voice}s. Therefore, we
1361 modify the @code{Staff} definition with the @code{\accepts}
1372 The opposite of @code{\accepts} is @code{\denies},
1373 which is sometimes needed when reusing existing context definitions.
1375 Putting both into a @code{\layout} block, like
1385 \accepts "ImproVoice"
1390 Then the output at the start of this subsection can be entered as
1398 c c_"while playing :)"
1405 @node Aligning contexts
1406 @subsection Aligning contexts
1408 New contexts may be aligned above or below exisiting contexts. This
1409 could be useful in setting up a vocal staff (@ref{Vocal ensembles}) and
1413 @findex alignAboveContext
1414 @findex alignBelowContext
1416 @lilypond[quote,ragged-right]
1417 ossia = { f4 f f f }
1419 \relative c' \new Staff = "main" {
1422 \new Staff \with {alignAboveContext=main} \ossia
1423 { d8 f d f d f d f }
1430 @node Vertical grouping of grobs
1431 @subsection Vertical grouping of grobs
1433 The VerticalAlignment and VerticalAxisGroup grobs work together.
1434 VerticalAxisGroup groups together different grobs like Staff, Lyrics,
1435 etc. VerticalAlignment then vertically aligns the different grobs
1436 grouped together by VerticalAxisGroup. There is usually only one
1437 VerticalAlignment per score but every Staff, Lyrics, etc. has its own
1441 @node The \override command
1442 @section The @code{\override} command
1444 In the previous section, we have already touched on a command that
1445 changes layout details: the @code{\override} command. In this section,
1446 we will look in more detail at how to use the command in practice. The
1447 general syntax of this command is:
1450 \override @var{context}.@var{layout_object} #'@var{layout_property} = #@var{value}
1453 This will set the @var{layout_property} of the specified @var{layout_object},
1454 which is a member of the @var{context}, to the @var{value}.
1457 * Constructing a tweak::
1458 * Navigating the program reference::
1459 * Layout interfaces::
1460 * Determining the grob property::
1461 * Objects connected to the input::
1462 * Using Scheme code instead of \tweak::
1463 * \set versus \override::
1464 * Difficult tweaks::
1469 @node Constructing a tweak
1470 @subsection Constructing a tweak
1472 Commands which change output generally look like
1475 \override Voice.Stem #'thickness = #3.0
1479 To construct this tweak we must determine these bits of information:
1482 @item the context: here @context{Voice}.
1483 @item the layout object: here @code{Stem}.
1484 @item the layout property: here @code{thickness}.
1485 @item a sensible value: here @code{3.0}.
1488 Some tweakable options are called @q{subproperties} and reside inside
1489 properties. To tweak those, use commands in the form
1492 \override Stem #'details #'beamed-lengths = #'(4 4 3)
1495 @cindex internal documentation
1496 @cindex finding graphical objects
1497 @cindex graphical object descriptions
1500 @cindex internal documentation
1502 For many properties, regardless of the data type of the property, setting the
1503 property to false ( @code{##f} ) will result in turning it off, causing
1504 Lilypond to ignore that property entirely. This is particularly useful for
1505 turning off grob properties which may otherwise be causing problems.
1507 We demonstrate how to glean this information from the notation manual
1508 and the program reference.
1513 @node Navigating the program reference
1514 @subsection Navigating the program reference
1516 Suppose we want to move the fingering indication in the fragment
1519 @lilypond[quote,fragment,relative=2,verbatim]
1525 If you visit the documentation on fingering instructions (in
1526 @ref{Fingering instructions}), you will notice:
1531 Program reference: @internalsref{Fingering}.
1536 @c outdated info; probably will delete.
1538 This fragment points to two parts of the program reference: a page
1539 on @code{FingerEvent} and one on @code{Fingering}.
1541 The page on @code{FingerEvent} describes the properties of the music
1542 expression for the input @code{-2}. The page contains many links
1543 forward. For example, it says
1546 Accepted by: @internalsref{Fingering_engraver},
1550 That link brings us to the documentation for the Engraver, the
1554 This engraver creates the following layout objects: @internalsref{Fingering}.
1557 In other words, once the @code{FingerEvent}s are interpreted, the
1558 @code{Fingering_engraver} plug-in will process them.
1562 @c I can't figure out what this is supposed to mean. -gp
1564 The @code{Fingering_engraver} is also listed to create
1565 @internalsref{Fingering} objects,
1567 @c old info? it doesn't make any sense to me with our current docs.
1569 second bit of information listed under @b{See also} in the Notation
1574 The programmer's reference is available as an HTML document. It is
1575 highly recommended that you read it in HTML form, either online or
1576 by downloading the HTML documentation. This section will be much more
1577 difficult to understand if you are using the
1581 Follow the link to @internalsref{Fingering}. At the top of the
1585 Fingering objects are created by: @internalsref{Fingering_engraver} and
1586 @internalsref{New_fingering_engraver}.
1589 By following related links inside the program reference, we can follow the
1590 flow of information within the program:
1594 @item @internalsref{Fingering}:
1595 @internalsref{Fingering} objects are created by:
1596 @internalsref{Fingering_engraver}
1598 @item @internalsref{Fingering_engraver}:
1599 Music types accepted: @internalsref{fingering-event}
1601 @item @internalsref{fingering-event}:
1602 Music event type @code{fingering-event} is in Music expressions named
1603 @internalsref{FingerEvent}
1606 This path goes against the flow of information in the program: it
1607 starts from the output, and ends at the input event. You could
1608 also start at an input event, and read with the flow of
1609 information, eventually ending up at the output object(s).
1611 The program reference can also be browsed like a normal document. It
1612 contains chapters on
1614 @internalsref{Music definitions},
1617 @code{Music definitions}
1619 on @internalsref{Translation}, and the @internalsref{Backend}. Every
1620 chapter lists all the definitions used and all properties that may be
1624 @node Layout interfaces
1625 @subsection Layout interfaces
1627 @cindex interface, layout
1628 @cindex layout interface
1631 The HTML page that we found in the previous section describes the
1632 layout object called @internalsref{Fingering}. Such an object is a
1633 symbol within the score. It has properties that store numbers (like
1634 thicknesses and directions), but also pointers to related objects. A
1635 layout object is also called a @emph{Grob}, which is short for Graphical
1636 Object. For more details about Grobs, see @internalsref{grob-interface}.
1638 The page for @code{Fingering} lists the definitions for the
1639 @code{Fingering} object. For example, the page says
1642 @code{padding} (dimension, in staff space):
1648 which means that the number will be kept at a distance of at least 0.5
1652 Each layout object may have several functions as a notational or
1653 typographical element. For example, the Fingering object
1654 has the following aspects
1658 Its size is independent of the horizontal spacing, unlike slurs or beams.
1661 It is a piece of text. Granted, it is usually a very short text.
1664 That piece of text is typeset with a font, unlike slurs or beams.
1667 Horizontally, the center of the symbol should be aligned to the
1668 center of the notehead.
1671 Vertically, the symbol is placed next to the note and the staff.
1674 The vertical position is also coordinated with other superscript
1675 and subscript symbols.
1678 Each of these aspects is captured in so-called @emph{interface}s,
1679 which are listed on the @internalsref{Fingering} page at the bottom
1682 This object supports the following interfaces:
1683 @internalsref{item-interface},
1684 @internalsref{self-alignment-interface},
1685 @internalsref{side-position-interface}, @internalsref{text-interface},
1686 @internalsref{text-script-interface}, @internalsref{font-interface},
1687 @internalsref{finger-interface}, and @internalsref{grob-interface}.
1690 Clicking any of the links will take you to the page of the respective
1691 object interface. Each interface has a number of properties. Some of
1692 them are not user-serviceable (@q{Internal properties}), but others
1695 We have been talking of @emph{the} @code{Fingering} object, but actually it
1696 does not amount to much. The initialization file (see
1697 @ref{Default files})
1698 @file{scm/@/define@/-grobs@/.scm} shows the soul of the @q{object},
1703 (avoid-slur . around)
1704 (slur-padding . 0.2)
1705 (staff-padding . 0.5)
1706 (self-alignment-X . 0)
1707 (self-alignment-Y . 0)
1708 (script-priority . 100)
1709 (stencil . ,ly:text-interface::print)
1710 (direction . ,ly:script-interface::calc-direction)
1711 (font-encoding . fetaNumber)
1712 (font-size . -5) ; don't overlap when next to heads.
1713 (meta . ((class . Item)
1714 (interfaces . (finger-interface
1716 text-script-interface
1718 side-position-interface
1719 self-alignment-interface
1720 item-interface))))))
1724 As you can see, the @code{Fingering} object is nothing more than a
1725 bunch of variable settings, and the webpage in the Program Reference
1726 is directly generated from this definition.
1729 @node Determining the grob property
1730 @subsection Determining the grob property
1732 Recall that we wanted to change the position of the @b{2} in
1734 @lilypond[quote,fragment,relative=2,verbatim]
1740 Since the @b{2} is vertically positioned next to its note, we have to
1741 meddle with the interface associated with this positioning. This is
1742 done using @code{side-position-interface}. The page for this interface
1746 @code{side-position-interface}
1748 Position a victim object (this one) next to other objects (the
1749 support). The property @code{direction} signifies where to put the
1750 victim object relative to the support (left or right, up or down?)
1755 Below this description, the variable @code{padding} is described as
1760 (dimension, in staff space)
1762 Add this much extra space between objects that are next to each other.
1766 By increasing the value of @code{padding}, we can move the
1767 fingering away from the notehead. The following command inserts
1768 3 staff spaces of white
1769 between the note and the fingering:
1771 \once \override Voice.Fingering #'padding = #3
1774 Inserting this command before the Fingering object is created,
1775 i.e., before @code{c2}, yields the following result:
1777 @lilypond[quote,relative=2,fragment,verbatim]
1778 \once \override Voice.Fingering #'padding = #3
1785 In this case, the context for this tweak is @context{Voice}. This
1786 fact can also be deduced from the program reference, for the page for
1787 the @internalsref{Fingering_engraver} plug-in says
1790 Fingering_engraver is part of contexts: @dots{} @internalsref{Voice}
1794 @node Objects connected to the input
1795 @subsection Objects connected to the input
1799 In some cases, it is possible to take a short-cut for tuning graphical
1800 objects. For objects that result directly from a piece of the input,
1801 you can use the @code{\tweak} function, for example
1803 @lilypond[relative=2,fragment,verbatim,ragged-right]
1806 \tweak #'color #red d
1808 \tweak #'duration-log #1 a
1809 >4-\tweak #'padding #10 -.
1812 As you can see, properties are set in the objects directly,
1813 without mentioning the grob name or context where this should be
1816 This technique only works for objects that are directly connected to
1817 an @internalsref{event} from the input, for example
1820 @item note heads, caused by chord-pitch (i.e., notes inside a chord)
1821 @item articulation signs, caused by articulation instructions
1824 It notably does not work for stems and accidentals (these are caused
1825 by note heads, not by music events) or clefs (these are not caused by
1826 music inputs, but rather by the change of a property value).
1828 There are very few objects which are @emph{directly} connected to
1829 output. A normal note (like @code{c4}) is not directly connected
1833 \tweak #'color #red c4
1837 does not change color. See @ref{Displaying music expressions}, for
1841 @node Using Scheme code instead of \tweak
1842 @subsection Using Scheme code instead of @code{\tweak}
1844 The main disadvantage of @code{\tweak} is its syntactical
1845 inflexibility. For example, the following produces a syntax error.
1848 F = \tweak #'font-size #-3 -\flageolet
1856 With other words, @code{\tweak} doesn't behave like an articulation
1857 regarding the syntax; in particular, it can't be attached with
1858 @samp{^} and @samp{_}.
1860 Using Scheme, this problem can be circumvented. The route to the
1861 result is given in @ref{Adding articulation to notes (example)},
1862 especially how to use @code{\displayMusic} as a helping guide.
1865 F = #(let ((m (make-music 'ArticulationEvent
1866 'articulation-type "flageolet")))
1867 (set! (ly:music-property m 'tweaks)
1868 (acons 'font-size -3
1869 (ly:music-property m 'tweaks)))
1878 Here, the @code{tweaks} properties of the flageolet object
1879 @samp{m} (created with @code{make-music}) are extracted with
1880 @code{ly:music-property}, a new key-value pair to change the
1881 font size is prepended to the property list with the
1882 @code{acons} Scheme function, and the result is finally
1883 written back with @code{set!}. The last element of the
1884 @code{let} block is the return value, @samp{m} itself.
1887 @node \set versus \override
1888 @subsection @code{\set} vs. @code{\override}
1890 We have seen two methods of changing properties: @code{\set} and
1891 @code{\override}. There are actually two different kinds of
1894 Contexts can have properties, which are usually named in
1895 @code{studlyCaps}. They mostly control the translation from
1896 music to notatino, eg. @code{localKeySignature} (for determining
1897 whether to print accidentals), @code{measurePosition} (for
1898 determining when to print a barline). Context properties can
1899 change value over time while interpreting a piece of music;
1900 @code{measurePosition} is an obvious example of
1901 this. Context properties are modified with @code{\set}.
1903 There is a special type of context property: the element
1904 description. These properties are named in @code{StudlyCaps}
1905 (starting with capital letters). They contain the
1906 @q{default settings} for said graphical object as an
1907 association list. See @file{scm/@/define@/-grobs@/.scm}
1908 to see what kind of settings there are. Element descriptions
1909 may be modified with @code{\override}.
1911 @code{\override} is actually a shorthand;
1914 \override @var{context}.@var{name} #'@var{property} = #@var{value}
1918 is more or less equivalent to
1920 @c leave this long line -gp
1922 \set @var{context}.@var{name} #'@var{property} = #(cons (cons '@var{property} @var{value}) <previous value of @var{context})
1925 The value of @code{context} (the alist) is used to initalize
1926 the properties of individual grobs. Grobs also have
1927 properties, named in Scheme style, with
1928 @code{dashed-words}. The values of grob properties change
1929 during the formatting process: formatting basically amounts
1930 to computing properties using callback functions.
1932 @code{fontSize} is a special property: it is equivalent to
1933 entering @code{\override ... #'font-size} for all pertinent
1934 objects. Since this is a common change, the special
1935 property (modified with @code{\set}) was created.
1938 @node Difficult tweaks
1939 @subsection Difficult tweaks
1941 There are a few classes of difficult adjustments.
1947 One type of difficult adjustment is the appearance of spanner objects,
1948 such as slur and tie. Initially, only one of these objects is created,
1949 and they can be adjusted with the normal mechanism. However, in some
1950 cases the spanners cross line breaks. If this happens, these objects
1951 are cloned. A separate object is created for every system that it is
1952 in. These are clones of the original object and inherit all
1953 properties, including @code{\override}s.
1956 In other words, an @code{\override} always affects all pieces of a
1957 broken spanner. To change only one part of a spanner at a line break,
1958 it is necessary to hook into the formatting process. The
1959 @code{after-line-breaking} callback contains the Scheme procedure that
1960 is called after the line breaks have been determined, and layout
1961 objects have been split over different systems.
1963 In the following example, we define a procedure
1964 @code{my-callback}. This procedure
1968 determines if we have been split across line breaks
1970 if yes, retrieves all the split objects
1972 checks if we are the last of the split objects
1974 if yes, it sets @code{extra-offset}.
1977 This procedure is installed into @internalsref{Tie}, so the last part
1978 of the broken tie is translated up.
1980 @lilypond[quote,verbatim,ragged-right]
1981 #(define (my-callback grob)
1983 ; have we been split?
1984 (orig (ly:grob-original grob))
1986 ; if yes, get the split pieces (our siblings)
1987 (siblings (if (ly:grob? orig)
1988 (ly:spanner-broken-into orig) '() )))
1990 (if (and (>= (length siblings) 2)
1991 (eq? (car (last-pair siblings)) grob))
1992 (ly:grob-set-property! grob 'extra-offset '(-2 . 5)))))
1995 \override Tie #'after-line-breaking =
2002 When applying this trick, the new @code{after-line-breaking} callback
2003 should also call the old one @code{after-line-breaking}, if there is
2004 one. For example, if using this with @code{Hairpin},
2005 @code{ly:hairpin::after-line-breaking} should also be called.
2008 @item Some objects cannot be changed with @code{\override} for
2009 technical reasons. Examples of those are @code{NonMusicalPaperColumn}
2010 and @code{PaperColumn}. They can be changed with the
2011 @code{\overrideProperty} function, which works similar to @code{\once
2012 \override}, but uses a different syntax.
2016 #"Score.NonMusicalPaperColumn" % Grob name
2017 #'line-break-system-details % Property name
2018 #'((next-padding . 20)) % Value
2021 Note, however, that @code{\override}, applied to
2022 @code{NoteMusicalPaperColumn} and @code{PaperColumn}, still works as
2023 expected within @code{\context} blocks.