@node Modifying context plug-ins
@subsection Modifying context plug-ins
-Notation contexts (like Score and Staff) not only store properties,
-they also contain plug-ins, called ``engravers'' that create notation
-elements. For example, the Voice context contains a
-@code{Note_head_engraver} and the Staff context contains a
+Notation contexts (like @code{Score} and @code{Staff}) not only
+store properties,
+they also contain plug-ins called ``engravers'' that create notation
+elements. For example, the @code{Voice} context contains a
+@code{Note_head_engraver} and the @code{Staff} context contains a
@code{Key_signature_engraver}.
For a full a description of each plug-in, see
It can be useful to shuffle around these plug-ins. This is done by
-starting a new context, with @code{\new} or @code{\context}, and
-modifying it like this,
+starting a new context with @code{\new} or @code{\context}, and
+modifying it,
@cindex @code{\with}
\remove @dots{}
@emph{etc.}
@}
-@emph{..music..}
+@{
+ @emph{..music..}
+@}
@end example
@noindent
@end lilypond
The @code{\override} must be done before the object is
-started. Therefore, when altering @emph{Spanner} objects, like slurs or
-beams, the @code{\override} command must be executed at the moment when
-the object is created. In this example,
-
+started. Therefore, when altering @emph{Spanner} objects such as slurs
+or beams, the @code{\override} command must be executed at the moment
+when the object is created. In this example,
@lilypond[quote,fragment,verbatim,relative=2]
\override Slur #'thickness = #3.0
@noindent
the slur is fatter but the beam is not. This is because the command for
-@code{Beam} comes after the Beam is started. Therefore it has no effect.
+@code{Beam} comes after the Beam is started, so it has no effect.
Analogous to @code{\unset}, the @code{\revert} command for a context
undoes an @code{\override} command; like with @code{\unset}, it only
@end example
Some tweakable options are called ``subproperties'' and reside inside
-properties. To tweak those, use
+properties. To tweak those, use commands of the form
+@c leave this as a long long
@example
-\override Stem #'details #'beamed-lengths = #'(4 4 3)
+\override @var{context}.@var{name} #'@var{property} #'@var{subproperty} = #@var{value}
+@end example
+
+@noindent
+such as
+
+@example
+\override Stem #'details #'beamed-lengths = #'(4 4 3)
@end example
The adjustments of the previous subsections (@ref{Changing context
properties on the fly}, @ref{Modifying context plug-ins}, and
@ref{Layout tunings within contexts}) can also be entered separately
-from the music, in the @code{\layout} block,
+from the music in the @code{\layout} block,
@example
\layout @{
@}
@end example
-Here
-@example
-\Staff
-@end example
-
-@noindent
-takes the existing definition for context @context{Staff} from the
+Here @code{\Staff} takes the existing definition for context @context{Staff} from the
identifier @code{\Staff}.
The statements
@end example
@noindent
-affect all staves in the score.
-
-Other contexts can be modified analogously.
+affect all staves in the score. Other contexts can be modified
+analogously.
The @code{\set} keyword is optional within the @code{\layout} block, so
@refbugs
-It is not possible to collect context changes in a variable, and apply
-them to one @code{\context} definition by referring to that variable.
+It is not possible to collect context changes in a variable and apply
+them to a @code{\context} definition by referring to that variable.
-The @code{\RemoveEmptyStaffContext} will override your current
-@code{\Staff} variable. If you wish to change the defaults for a
-staff that uses @code{\RemoveEmptyStaffContext}, you must do so
+The @code{\RemoveEmptyStaffContext} will overwrite your current
+@code{\Staff} settings. If you wish to change the defaults for a
+staff which uses @code{\RemoveEmptyStaffContext}, you must do so
after calling @code{\RemoveemptyStaffContext}, ie
@example
@subsection Defining new contexts
Specific contexts, like @context{Staff} and @code{Voice}, are made of
-simple building blocks, and it is possible to compose engraver
-plug-ins in different combinations, thereby creating new types of
-contexts.
+simple building blocks. It is possible to create new types of
+contexts with different combinations of engraver plug-ins.
The next example shows how to build a different type of
@context{Voice} context from scratch. It will be similar to
-@code{Voice}, but prints centered slash noteheads only. It can be used
-to indicate improvisation in Jazz pieces,
+@code{Voice}, but only prints centered slash noteheads. It can be used
+to indicate improvisation in jazz pieces,
@lilypond[quote,ragged-right]
\layout { \context {
@end lilypond
-These settings are again done within a @code{\context} block inside a
+These settings are defined within a @code{\context} block inside a
@code{\layout} block,
@example
In the following discussion, the example input shown should go on the
@dots{} in the previous fragment.
-First, the context gets a name. Instead of @context{Voice} it
+First the context's name is defined. Instead of @context{Voice} it
will be called @context{ImproVoice},
@example
position to the value of @code{squashedPosition}, in this case@tie{}@code{0},
the center line.
-The notes look like a slash, without a stem,
+The notes look like a slash, and have no stem,
@example
\override NoteHead #'style = #'slash
\override Stem #'transparent = ##t
@end example
-
All these plug-ins have to cooperate, and this is achieved with a
special plug-in, which must be marked with the keyword @code{\type}.
This should always be @internalsref{Engraver_group},
@}
@end example
+@cindex @code{\accepts}
Contexts form hierarchies. We want to hang the @context{ImproVoice}
under @context{Staff}, just like normal @code{Voice}s. Therefore, we
modify the @code{Staff} definition with the @code{\accepts}
-command,@footnote{The opposite of @code{\accepts} is @code{\denies},
-which is sometimes needed when reusing existing context definitions.}
-
-
+command,
@example
\context @{
@}
@end example
+@cindex @code{\denies}
+The opposite of @code{\accepts} is @code{\denies},
+which is sometimes needed when reusing existing context definitions.
+
Putting both into a @code{\layout} block, like
@example
In the previous section, we have already touched on a command that
changes layout details: the @code{\override} command. In this section,
we will look in more detail at how to use the command in practice.
-First, we will give a few versatile commands that are sufficient
-for many situations. The next section will discuss the general use of
-@code{\override}.
@menu
@node Constructing a tweak
@subsection Constructing a tweak
-The general procedure of changing output, that is, entering
-a command like
+Commands which change output generally look like
@example
\override Voice.Stem #'thickness = #3.0
@end example
@noindent
-means that we have to determine these bits of information:
+This means that we must determine these bits of information:
@itemize
@item the context: here @context{Voice}.
@item the layout object: here @code{Stem}.
-@item the layout property: here @code{thickness}
-@item a sensible value: here @code{3.0}
+@item the layout property: here @code{thickness}.
+@item a sensible value: here @code{3.0}.
@end itemize
Some tweakable options are called ``subproperties'' and reside inside
-properties. To tweak those, use
+properties. To tweak those, use commands in the form
@example
\override Stem #'details #'beamed-lengths = #'(4 4 3)
We demonstrate how to glean this information from the notation manual
and the program reference.
+
@node Navigating the program reference
@subsection Navigating the program reference
@end lilypond
If you visit the documentation on fingering instructions (in
-@ref{Fingering instructions}), you will notice that there is written:
+@ref{Fingering instructions}), you will notice:
@quotation
@seealso
-Program reference: @internalsref{FingerEvent} and @internalsref{Fingering}.
+Program reference: @internalsref{Fingering}.
@end quotation
-
+@c outdated info; probably will delete.
+@ignore
This fragment points to two parts of the program reference: a page
on @code{FingerEvent} and one on @code{Fingering}.
In other words, once the @code{FingerEvent}s are interpreted, the
@code{Fingering_engraver} plug-in will process them.
+@end ignore
@ignore
@c I can't figure out what this is supposed to mean. -gp
manual.
@end ignore
+Follow the link to @internalsref{Fingering}. At the top of the
+page, you will see
+
+@quotation
+Fingering objects are created by: @internalsref{Fingering_engraver} and
+@internalsref{New_fingering_engraver}.
+@end quotation
+
By clicking around in the program reference, we can follow the
-flow of information within the program, either forward (like we did
-here), or backwards, following links like this:
+flow of information within the program, following links like this:
@itemize @bullet
@end itemize
This path goes against the flow of information in the program: it
-starts from the output, and ends at the input event.
+starts from the output, and ends at the input event. You could
+also start at an input event, and read with the flow of
+information, eventually ending up at the output object(s).
The program reference can also be browsed like a normal document. It
-contains a chapter on
+contains chapters on
@ifhtml
@internalsref{Music definitions},
@end ifhtml
@code{Music definitions}
@end ifnothtml
on @internalsref{Translation}, and the @internalsref{Backend}. Every
-chapter lists all the definitions used, and all properties that may be
+chapter lists all the definitions used and all properties that may be
tuned.
@cindex layout interface
@cindex grob
-The HTML page that we found in the previous section, describes the
+The HTML page that we found in the previous section describes the
layout object called @internalsref{Fingering}. Such an object is a
symbol within the score. It has properties that store numbers (like
thicknesses and directions), but also pointers to related objects. A
@quotation
@code{padding} (dimension, in staff space):
-@code{0.6}
+@code{0.5}
@end quotation
@noindent
Vertically, the symbol is placed next to the note and the staff.
@item
-The vertical position is also coordinated with other super- and subscript
-symbols.
+The vertical position is also coordinated with other superscript
+and subscript symbols.
@end itemize
Each of these aspects is captured in so-called @emph{interface}s,
Clicking any of the links will take you to the page of the respective
object interface. Each interface has a number of properties. Some of
them are not user-serviceable (``Internal properties''), but others
-are.
+can be modified.
We have been talking of @emph{the} @code{Fingering} object, but actually it
-does not amount to much. The initialization file
+does not amount to much. The initialization file (see
+@ref{Default files})
@file{scm/@/define@/-grobs@/.scm} shows the soul of the `object',
@example
bunch of variable settings, and the webpage in the Program Reference
is directly generated from this definition.
+
@node Determining the grob property
@subsection Determining the grob property
-
Recall that we wanted to change the position of the @b{2} in
@lilypond[quote,fragment,relative=2,verbatim]
@cindex padding
@noindent
-below this description, the variable @code{padding} is described as
+Below this description, the variable @code{padding} is described as
@quotation
@table @code
@end table
@end quotation
-By increasing the value of @code{padding}, we can move away the
-fingering. The following command inserts 3 staff spaces of white
+By increasing the value of @code{padding}, we can move the
+fingering away from the notehead. The following command inserts
+3 staff spaces of white
between the note and the fingering:
@example
\once \override Voice.Fingering #'padding = #3
Fingering_engraver is part of contexts: @dots{} @b{@internalsref{Voice}}
@end quotation
+
@node Objects connected to the input
@subsection Objects connected to the input
an @internalsref{event} from the input, for example
@itemize @bullet
-@item note heads, caused by chord-pitch.
-@item articulation signs, caused by articulation instructions
+@item note heads, caused by chord-pitch (i.e., notes inside a chord).
+@item articulation signs, caused by articulation instructions.
@end itemize
It notably does not work for stems and accidentals (these are caused
by note heads, not by music events) or clefs (these are not caused by
music inputs, but rather by the change of a property value).
-
+
+There are very few objects which are @emph{directly} connected to
+output. A normal note (like @code{c4}) is not directly connected
+to output, so
+
+@example
+\tweak #'color #red c4
+@end example
+
+@noindent
+will not change color. See @ref{Displaying music expressions} for
+details.
+
@node Difficult tweaks
@subsection Difficult tweaks
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