@node Tweaking methods
@subsection Tweaking methods
+@strong{\override command}
+
+@cindex override command
+@funindex \override
+
We have already met the commands @code{\set} and @code{\with},
used to change the properties of @strong{contexts} and to remove
and add @strong{engravers}, in
@ref{Modifying context properties} and @ref{Adding
-and removing engravers}. We now must meet one more command.
+and removing engravers}. We now must meet one more important
+command.
The command to change the properties of @strong{layout objects} is
@code{\override}. Because this command has to modify
@noindent
This will set the property with the name @emph{layout_property}
-of the layout object with the name
+of the layout object with the name
@emph{layout_object}, which is a member of the @emph{context}
context, to the value @emph{value}.
@emph{context} is often not needed. It will be omitted
in many of the following examples.
-There is another form of the override command,
+@strong{\overrideProperty command}
+
+@cindex overrideProperty command
+@funindex \overrideProperty
+
+There is another form of the override command,
@code{\overrideProperty}, which is occasionally required.
-We mention it here for completeness, but for details see
+We mention it here for completeness, but for details see
@ruser{Difficult tweaks}.
@c Maybe explain in a later iteration -td
+@strong{\tweak command}
+
+@cindex tweak command
+@funindex \tweak
+
The final tweaking command which is available is @code{\tweak}.
This should be used to change the properties of objects which
occur at the same musical moment, such as the notes within a
chord. Using @code{\override} would affect all the notes
within a chord, whereas @code{\tweak} affects just the following
-item in the input stream. You may find the details in
+item in the input stream.
+
+Here's an example. Suppose we wish to change the size of the
+middle note (the E) in a C major chord. Let's first see what
+@code{\once \override} would do:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=1]
+ <c e g>4
+ \once \override NoteHead #'font-size = #-3
+ <c e g>4
+@end lilypond
+
+We see the override affects @emph{all} the notes in the chord.
+This is because all the notes of a chord occur at the same
+@emph{musical moment}, and the action of @code{\once} is to
+apply the override to all layout objects of the type specified
+which occur at the same musical moment as the @code{\override}
+command itself.
+
+The @code{\tweak} command operates in a different way. It acts
+on the immediately following item in the input stream. However,
+it is effective only on objects which are created directly from
+the input stream, essentially note heads and articulations.
+(Objects such as stems and accidentals are created later and
+cannot be tweaked in this way). Furthermore, when it is applied
+to note heads these must be within a chord, i.e., within single
+angle brackets, so to tweak a single note the @code{\tweak}
+command must be placed inside single angle brackets with the
+note.
+
+So to return to our example, the size of the middle note of
+a chord would be changed in this way:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=1]
+ <c e g>4
+ <c \tweak #'font-size #-3 e g>4
+@end lilypond
+
+Note that the syntax of @code{\tweak} is different from that
+of the @code{\override} command. Neither the context nor the
+layout object should be specified; in fact, it would generate
+an error to do so. These are both implied by the following
+item in the input stream. So the general syntax of the
+@code{\tweak} command is simply:
+
+@example
+\tweak #'@emph{layout_property} = #@emph{value}
+@end example
+
+A @code{\tweak} command can also be used to modify just one in
+a series of articulations, as shown here:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
+a ^Black
+ -\tweak #'color #red ^Red
+ -\tweak #'color #green _Green
+@end lilypond
+
+Note that the @code{\tweak} command must be preceded by an
+articulation mark as if it were an articulation itself.
+
+You can find more details of the @code{\tweak} command in
@ruser{Objects connected to the input}.
+
@node The Internals Reference manual
@section The Internals Reference manual
@cindex Internals Reference
@menu
-* Properties of layout objects::
-* Properties found in interfaces::
-* Types of properties::
+* Properties of layout objects::
+* Properties found in interfaces::
+* Types of properties::
@end menu
@node Properties of layout objects
at first, so we can be sure the command is working. We get:
@example
- \override Slur #'thickness = #5.0
+\override Slur #'thickness = #5.0
@end example
Don't forget the @code{#'} preceding the
in italics should be
@example
- \override LyricText #'font-shape = #'italic
+\override LyricText #'font-shape = #'italic
@end example
@noindent
the interpreter cannot recognise them. So the command should be:
@example
- \override Lyrics . LyricText #'font-shape = #'italic
+\override Lyrics . LyricText #'font-shape = #'italic
@end example
@warning{In lyrics always leave whitespace between the final
@item @code{BarNumber} @tab @code{ 100}
@end multitable
-If the default values of @code{outside-staff-priority} does not
+If the default values of @code{outside-staff-priority} do not
give you the placing you want, the priority of any of the objects
may be overridden. Suppose we would
like the ottava bracket to be placed below the text spanner in the
Let's now see how the properties in the previous section can
help to resolve overlapping notation.
-@subheading @code{padding} property
+@subheading padding property
@cindex padding property
The @code{padding} property can be set to increase
If the @code{padding} property of an object is increased when that
object is in a stack of objects being positioned according to
-their @code{outside-staff-priority}, then that object and all
+their @code{outside-staff-priority}, then that object and all
objects outside it are moved.
-
-@subheading left-padding and right-padding properties
+
+@subheading left-padding and right-padding
@cindex left-padding property
@cindex right-padding property
-TODO Example showing the utility of these properties -td
+The @code{right-padding} property affects the spacing between the
+accidental and the note to which it applies. It is not often
+required, but the following example shows one situation where it
+is needed. Suppose we wish to show a chord containing both
+a B-natural and a B-flat. To avoid ambiguity we would like to
+precede the notes with both a natural and a flat sign. Here
+are a few attempts to do this:
+
+@lilypond[quote,fragment,ragged-right,verbatim,relative=2]
+<b bes>
+<b! bes>
+<b? bes>
+@end lilypond
+
+None work, with the second two showing bad collisions between
+the two signs.
+
+One way of achieving this is to override the accidental stencil
+with a markup containing the natural and flat symbols in the
+order we would like, like this:
+
+@lilypond[quote,ragged-right,verbatim]
+naturalplusflat = \markup { \natural \flat }
+\relative c'' {
+ \once \override Accidental
+ #'stencil = #ly:text-interface::print
+ \once \override Accidental #'text = #naturalplusflat
+ \once \override Score.AccidentalPlacement #'right-padding = #1.5
+ <b bes>
+}
+@end lilypond
+
+@noindent
+This necessarily uses an override for the accidental stencil which
+will not be covered until later. The stencil type must be a
+procedure, here changed to print the contents of the @code{text}
+property of @code{Accidental}, which itself is set to be a natural
+sign followed by a flat sign. These are then moved further away
+from the note head by overriding @code{right-padding}.
+
+@noindent
@subheading staff-padding property
@cindex staff-padding property
@end lilypond
-@subheading force-hshift property
-@cindex force-hshift property
-@c FIXME: formatting stuff (ie not important right now IMO)
-@c @a nchor Chopin finally corrected TODOgp
-
-We can now see how to apply the final corrections to the Chopin
-example introduced at the end of @ref{I'm hearing Voices}, which
-was left looking like this:
-
-@lilypond[quote,verbatim,fragment,ragged-right]
-\new Staff \relative c'' {
- \key aes \major
- <<
- { c2 aes4. bes8 } \\
- { aes2 f4 fes } \\
- { \voiceFour
- <ees c>2
- des2
- }
- >> |
- <c ees aes c>1 |
-}
-@end lilypond
-
-@noindent
-The lower two notes of the first chord (i.e,
-those in the third voice) should not be shifted away from the
-note column of the higher two notes. To correct this we set
-@code{force-hshift}, which is a property of
-@code{NoteColumn}, of these notes to zero.
-The lower note of the second chord is best placed just to the
-right of the higher notes. We achieve this by setting
-@code{force-hshift} of this note to 0.5, ie half a note head's
-width to the right of the note column of the higher notes.
-
-Here's the final result:
-
-@lilypond[quote,verbatim,fragment,ragged-right]
-\new Staff \relative c'' {
- \key aes \major
- <<
- { c2 aes4. bes8 } \\
- { aes2 f4 fes } \\
- { \voiceFour
- \once \override NoteColumn #'force-hshift = #0 <ees c>2
- \once \override NoteColumn #'force-hshift = #0.5 des2
- }
- >> |
- <c ees aes c>1 |
-}
-@end lilypond
-
-
@subheading positions property
@cindex positions property
@end lilypond
@noindent
-This can only be resolved by manually moving both ends of the beam
+This can be resolved by manually moving both ends of the beam
up from their position at 2 staff-spaces above the center line to,
say, 3:
the second block of quavers, but not to any of the beams in the
second voice.
+@subheading force-hshift property
+@cindex force-hshift property
+@c FIXME: formatting stuff (ie not important right now IMO)
+@c @a nchor Chopin finally corrected TODOgp
+
+We can now see how to apply the final corrections to the Chopin
+example introduced at the end of @ref{I'm hearing Voices}, which
+was left looking like this:
+
+@lilypond[quote,verbatim,fragment,ragged-right]
+\new Staff \relative c'' {
+ \key aes \major
+ <<
+ { c2 aes4. bes8 } \\
+ { aes2 f4 fes } \\
+ { \voiceFour
+ <ees c>2
+ des2
+ }
+ >> |
+ <c ees aes c>1 |
+}
+@end lilypond
+
+@noindent
+The lower two notes of the first chord (i.e,
+those in the third voice) should not be shifted away from the
+note column of the higher two notes. To correct this we set
+@code{force-hshift}, which is a property of
+@code{NoteColumn}, of these notes to zero.
+The lower note of the second chord is best placed just to the
+right of the higher notes. We achieve this by setting
+@code{force-hshift} of this note to 0.5, ie half a note head's
+width to the right of the note column of the higher notes.
+
+Here's the final result:
+
+@lilypond[quote,verbatim,fragment,ragged-right]
+\new Staff \relative c'' {
+ \key aes \major
+ <<
+ { c2 aes4. bes8 } \\
+ { aes2 f4 fes } \\
+ { \voiceFour
+ \once \override NoteColumn #'force-hshift = #0 <ees c>2
+ \once \override NoteColumn #'force-hshift = #0.5 des2
+ }
+ >> |
+ <c ees aes c>1 |
+}
+@end lilypond
+
+
@node Real music example
@subsection Real music example
@section Further tweaking
@menu
-* Other uses for tweaks::
-* Using variables for tweaks::
-* Other sources of information::
-* Advanced tweaks with Scheme::
-* Avoiding tweaks with slower processing::
+* Other uses for tweaks::
+* Using variables for tweaks::
+* Other sources of information::
+* Avoiding tweaks with slower processing::
+* Advanced tweaks with Scheme::
@end menu
@node Other uses for tweaks
@itemize
-@cindex transparent property
+@cindex transparent property, use of
@cindex objects, making invisible
@cindex removing objects
@cindex objects, removing
@cindex hiding objects
@cindex invisible objects
+@cindex tying notes across voices
@item
-Setting the @code{transparent} property will cause an object
-to be printed in @q{invisible ink}: the object is not printed,
-but all its other behavior is retained. The object still takes
-up space, it takes part in collisions, and slurs, ties, and beams
-can be attached to it.
+@subheading Tying notes across voices
-The following example demonstrates how to connect different voices
-using ties. Normally, ties only connect two notes in the same
-voice. By introducing a tie in a different voice,
+The following example demonstrates how to connect notes in
+different voices using ties. Normally, only two notes in the
+same voice can be connected with ties. By using two voices,
+with the tied notes in one of them
@lilypond[quote,fragment,relative=2]
-<< {
- b8~ b8\noBeam
-} \\ {
- b[ g8]
-} >>
+<< { b8~ b8\noBeam }
+\\ { b[ g8] }
+>>
@end lilypond
@noindent
-and blanking the first up-stem in that voice, the tie appears to cross
-voices:
+and blanking the first up-stem in that voice, the tie appears to
+cross voices:
@lilypond[quote,fragment,relative=2,verbatim]
-<< {
- \once \override Stem #'transparent = ##t
- b8~ b8\noBeam
-} \\ {
- b[ g8]
-} >>
+<<
+ {
+ \once \override Stem #'transparent = ##t
+ b8~ b8\noBeam
+ }
+\\
+ { b[ g8] }
+>>
@end lilypond
-To make sure that the just-blanked stem doesn't squeeze the tie too much,
-we also lengthen the stem, by setting the @code{length} to
-@code{8},
+To make sure that the just-blanked stem doesn't squeeze the tie
+too much, we can lengthen the stem by setting the
+@code{length} to @code{8},
@lilypond[quote,fragment,relative=2,verbatim]
-<< {
- \once \override Stem #'transparent = ##t
- \once \override Stem #'length = #8
- b8~ b8\noBeam
-} \\ {
- b[ g8]
-} >>
+<<
+ {
+ \once \override Stem #'transparent = ##t
+ \once \override Stem #'length = #8
+ b8~ b8\noBeam
+ }
+\\
+ { b[ g8] }
+>>
@end lilypond
-@cindex stencil property
-
@item
+@subheading Simulating a fermata
+
+@cindex stencil property, use of
+@cindex fermata, implementing in MIDI
+
For outside-staff objects it is usually better to override the
object's @code{stencil} property rather than its @code{transparent}
-property when you wish to remove it from the printed output.
+property when you wish to remove it from the printed output.
Setting the @code{stencil} property of an object to @code{#f} will
remove that object entirely from the printed output. This means it
has no effect on the placement of other objects placed relative to
For example, if we wished to change the metronome setting in order
to simulate a fermata in the MIDI output we would not want the
-metronome marking to appear in the printed output, and we would
+metronome markings to appear in the printed output, and we would
not want it to influence the spacing between the two systems or
-the spacing of the notes on the staff. So setting its
+the spacing of the notes on the staff. So setting its
@code{stencil} property to @code{#f} would be the best way.
We show here the effect of the two methods:
-@lilypond[quote,verbatim]
+@lilypond[quote,verbatim,ragged-right]
\score {
\relative c'' {
% Visible tempo marking
\tempo 4=120
a a a a
}
+ \layout { }
\midi { }
}
@end lilypond
@node Using variables for tweaks
@subsection Using variables for tweaks
-TODO Add section
+Override commands are often long and tedious to type, and they
+have to be absolutely correct. If the same overrides are to be
+used many times it may be worth defining variables to hold them.
+Suppose we wish to emphasize certain words in lyrics by printing
+them in bold italics. The @code{\italic} and @code{\bold}
+commands do not work within lyrics so we must instead use the
+following @code{\override} and @code{\revert} commands:
-@node Other sources of information
-@subsection Other sources of information
+@example
+@code{\override Lyrics . LyricText #'font-shape = #'italic}
+@code{\override Lyrics . LyricText #'font-series = #'bold}
-The Internals Reference documentation contains a lot of information
-about LilyPond, but even more information can be gathered from
-looking at the internal LilyPond files.
+@code{\revert Lyrics . LyricText #'font-shape}
+@code{\revert Lyrics . LyricText #'font-series}
+@end example
-TODO Show example, then explain where to find ly/propert-ly.
+These would be extremely tedious to enter if there were many words
+requiring emphasis. So instead we define these as two variables,
+and use them as follows:
-Some default settings (such as the definitions for
-@code{\header@{@}}s) are stored as @code{.ly} files. Other
-settings (such as the definitions of markup commands) are
-stored as @code{.scm} (Scheme) files. Further explanation is
-outside the scope of this manual; users should be warned that
-a substantial amount of technical knowledge or time is required
-to understand these files.
+@lilypond[quote,verbatim]
+emph = {
+ \override Lyrics . LyricText #'font-shape = #'italic
+ \override Lyrics . LyricText #'font-series = #'bold
+}
+norm = {
+ \revert Lyrics . LyricText #'font-shape
+ \revert Lyrics . LyricText #'font-series
+}
-@itemize
+global = { \time 4/4 \partial 4 \key c \major}
+SopMusic = \relative c' { c4 | e4. e8 g4 g | a a g }
+AltoMusic = \relative c' { c4 | c4. c8 e4 e | f f e }
+TenorMusic = \relative c { e4 | g4. g8 c4. b8 | a8 b c d e4 }
+BassMusic = \relative c { c4 | c4. c8 c4 c | f8 g a b c4 }
+VerseOne = \lyrics { E -- | ter -- nal \emph Fa -- ther, \norm | strong to save, }
+VerseTwo = \lyricmode { O | \emph Christ, \norm whose voice the | wa -- ters heard, }
+VerseThree = \lyricmode { O | \emph Ho -- ly Spi -- rit, \norm | who didst brood }
+VerseFour = \lyricmode { O | \emph Tri -- ni -- ty \norm of | love and pow'r }
-@item Linux: @file{@var{installdir}/lilypond/usr/share/lilypond/current/}
+\score {
+ \new ChoirStaff <<
+ \new Staff <<
+ \clef "treble"
+ \new Voice = "Sop" { \voiceOne \global \SopMusic }
+ \new Voice = "Alto" { \voiceTwo \AltoMusic }
+ \new Lyrics \lyricsto "Sop" { \VerseOne }
+ \new Lyrics \lyricsto "Sop" { \VerseTwo }
+ \new Lyrics \lyricsto "Sop" { \VerseThree }
+ \new Lyrics \lyricsto "Sop" { \VerseFour }
+ >>
+ \new Staff <<
+ \clef "bass"
+ \new Voice = "Tenor" { \voiceOne \TenorMusic }
+ \new Voice = "Bass" { \voiceTwo \BassMusic }
+ >>
+ >>
+}
+@end lilypond
-@item OSX:
-@file{@var{installdir}/LilyPond.app/Contents/Resources/share/lilypond/current/}.
-To access this, either @code{cd} into this directory from the
-Terminal, or control-click on the LilyPond application and select
-@q{Show Package Contents}.
-@item Windows: @file{@var{installdir}/LilyPond/usr/share/lilypond/current/}
-@end itemize
+@node Other sources of information
+@subsection Other sources of information
-The @file{ly/} and @file{scm/} directories will be of
-particular interest. Files such as @file{ly/property-init.ly} and
-@file{ly/declarations-init.ly} define all the common tweaks.
+The Internals Reference documentation contains a lot of information
+about LilyPond, but even more information can be gathered by
+looking at the internal LilyPond files. To explore these, first
+find the directory appropriate to your system, as follows:
+@strong{Linux}
-@node Advanced tweaks with Scheme
-@subsection Advanced tweaks with Scheme
+Navigate to
+@file{@var{installdir}/lilypond/usr/share/lilypond/current/}
-We have seen how LilyPond output can be heavily modified using
-commands like
-@code{\override TextScript #'extra-offset = ( 1 . -1)}. But
-we have even more power if we use Scheme. For a full explantion
-of this, see the @ref{Scheme tutorial}, and
-@ruser{Interfaces for programmers}.
+@strong{OSX}
-We can use Scheme to simply @code{\override} commands,
+Navigate to
+@file{@var{installdir}/LilyPond.app/Contents/Resources/share/lilypond/current/}
+by either @code{cd}-ing into this directory from the
+Terminal, or control-clicking on the LilyPond application and
+selecting @q{Show Package Contents}.
-TODO Check this is a valid example with skylining
+@strong{Windows}
-@lilypond[quote,verbatim,ragged-right]
-padText = #(define-music-function (parser location padding) (number?)
-#{
- \once \override TextScript #'padding = #$padding
-#})
-
-\relative c''' {
- c4^"piu mosso" b a b
- \padText #1.8
- c4^"piu mosso" d e f
- \padText #2.6
- c4^"piu mosso" fis a g
-}
-@end lilypond
+Using Windows Explorer, navigate to
+@file{@var{installdir}/LilyPond/usr/share/lilypond/current/}
-We can use it to create new commands,
+Within this directory the two interesting subdirectories are
-TODO Check this is a valid example with skylining
+@itemize
+@item @file{../ly/ } - contains files in LilyPond format
+@item @file{../scm/} - contains files in Scheme format
+@end itemize
-@lilypond[quote,verbatim,ragged-right]
-tempoMark = #(define-music-function (parser location padding marktext)
- (number? string?)
-#{
- \once \override Score . RehearsalMark #'padding = $padding
- \once \override Score . RehearsalMark #'extra-spacing-width = #'(+inf.0 . -inf.0)
- \mark \markup { \bold $marktext }
-#})
+Let's begin by looking at some files in @file{../ly/}.
+Open @file{../ly/property-init.ly} in a text editor. The one
+you normally use for @code{.ly} files will be fine. This file
+contains the definitions of all the standard LilyPond built-in
+commands, such as @code{\stemUp} and @code{\slurDotted}. You will
+see that these are nothing more than definitions of variables
+containing one or a group of @code{\override} commands. For
+example, @code{/tieDotted} is defined to be:
-\relative c'' {
- c2 e
- \tempoMark #3.0 #"Allegro"
- g c
-}
-@end lilypond
+@example
+tieDotted = @{
+ \override Tie #'dash-period = #0.75
+ \override Tie #'dash-fraction = #0.1
+@}
+@end example
-Even music expressions can be passed in.
+If you do not like the default values these built-in commands can
+be redefined easily, just like any other variable, at the
+head of your input file.
+
+The following are the most useful files to be found in
+@file{../ly/}:
+
+@multitable @columnfractions .4 .6
+@headitem Filename
+ @tab Contents
+@item @file{../ly/engraver-init.ly}
+ @tab Definitions of engraver Contexts
+@item @file{../ly/paper-defaults.ly}
+ @tab Specifications of paper-related defaults
+@item @file{../ly/performer-init.ly}
+ @tab Definitions of performer Contexts
+@item @file{../ly/property-init.ly}
+ @tab Definitions of all common built-in commands
+@end multitable
+
+Other settings (such as the definitions of markup commands) are
+stored as @code{.scm} (Scheme) files. The Scheme programming
+language is used to provide a programmable interface into
+LilyPond internal operation. Further explanation of these files
+is currently outside the scope of this manual, as a knowledge of
+the Scheme language is required. Users should be warned that
+a substantial amount of technical knowledge or time is required
+to understand Scheme and these files (see @ref{Scheme tutorial}).
+
+If you have this knowledge, the Scheme files which may be of
+interest are:
+
+@multitable @columnfractions .4 .6
+@headitem Filename
+ @tab Contents
+@item @file{../scm/auto-beam.scm}
+ @tab Sub-beaming defaults
+@item @file{../scm/define-grobs.scm}
+ @tab Default settings for grob properties
+@item @file{../scm/define-markup-commands.scm}
+ @tab Specify all markup commands
+@item @file{../scm/midi.scm}
+ @tab Default settings for MIDI output
+@item @file{../scm/output-lib.scm}
+ @tab Settings that affect appearance of frets, colors,
+ accidentals, bar lines, etc
+@item @file{../scm/parser-clef.scm}
+ @tab Definitions of supported clefs
+@item @file{../scm/script.scm}
+ @tab Default settings for articulations
+@end multitable
-@lilypond[quote,verbatim,ragged-right]
-pattern = #(define-music-function (parser location x y) (ly:music? ly:music?)
-#{
- $x e8 a b $y b a e
-#})
-
-\relative c''{
- \pattern c8 c8\f
- \pattern {d16 dis} { ais16-> b\p }
-}
-@end lilypond
@node Avoiding tweaks with slower processing
@subsection Avoiding tweaks with slower processing
LilyPond can perform extra checks while it processes files. These
-commands will take extra time, but the result may require fewer
-manual tweaks.
+checks will take extra time to perform, but fewer manual tweaks
+may be required to obtain an acceptable result. If a text script
+or part of the lyrics extends over the margins these checks will
+compress that line of the score just enough to fit within the
+margins.
+
+To be effective under all circumstances these checks must be enabled
+by placing the overrides in a Score @code{\with} block, rather than
+in-line in music, as follows:
@example
-%% makes sure text scripts and lyrics are within the paper margins
-\override Score.PaperColumn #'keep-inside-line = ##t
-\override Score.NonMusicalPaperColumn #'keep-inside-line = ##t
+\new Score \with @{
+ % Makes sure text scripts and lyrics are within the paper margins
+ \override PaperColumn #'keep-inside-line = ##t
+ \override NonMusicalPaperColumn #'keep-inside-line = ##t
+@} @{
+ ..
+@}
@end example
-In some cases (see issue 246), this must be done before
-@code{\override} commands can be processed.
+@node Advanced tweaks with Scheme
+@subsection Advanced tweaks with Scheme
-@verbatim
-\new Score \with {
- \override PaperColumn #'keep-inside-line = ##t
- \override NonMusicalPaperColumn #'keep-inside-line = ##t
- } {
- ..
+Although many things are possible with the @code{\override} and
+@code{\tweak} commands, an even more powerful way of modifying
+the action of LilyPond is available through a programmable
+interface to the LilyPond internal operation. Code written in
+the Scheme programming language can be incorporated directly in
+the internal operation of LilyPond. Of course, at least a basic
+knowledge of programming in Scheme is required to do this, and an
+introduction is provided in the @ref{Scheme tutorial}.
+
+As an illustration of one of the many possibilities, instead of
+setting a property to a constant it can be set to a Scheme
+procedure which is then called whenever that property is accessed
+by LilyPond. The property can then be set dynamically to a value
+determined by the procedure at the time it is called. In this
+example we color the note head in accordance with its position on
+the staff.
+
+@lilypond[quote,verbatim,ragged-right]
+#(define (color-notehead grob)
+ "Color the notehead according to its position on the staff."
+ (let ((mod-position (modulo (ly:grob-property grob 'staff-position) 7)))
+ (case mod-position
+ ;; Return rainbow colors
+ ((1) (x11-color 'red )) ; for C
+ ((2) (x11-color 'orange )) ; for D
+ ((3) (x11-color 'yellow )) ; for E
+ ((4) (x11-color 'green )) ; for F
+ ((5) (x11-color 'blue )) ; for G
+ ((6) (x11-color 'purple )) ; for A
+ ((0) (x11-color 'violet )) ; for B
+ )
+ )
+)
+
+\relative c' {
+ % Arrange to obtain color from color-notehead procedure
+ \override NoteHead #'color = #color-notehead
+ c2 c' |
+ b4 g8 a b4 c |
+ c,2 a' |
+ g1 |
}
-@end verbatim
+\addlyrics {
+ Some -- where o -- ver the Rain -- bow way up high,
+}
+@end lilypond
+
+Further examples showing the use of these programmable interfaces
+can be found in @ref{Tweaking with Scheme}.
projects / lilypond.git / blobdiff