grob-interface - LilyPond program-reference
Description: LilyPond program-reference

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#### grob-interface

A grob represents a piece of music notation

All grobs have an X and Y-position on the page. These X and Y positions are stored in a relative format, so they can easily be combined by stacking them, hanging one grob to the side of another, and coupling them into a grouping objects.

Each grob has a reference point (a.k.a. parent): the position of a grob is stored relative to that reference point. For example the X-reference point of a staccato dot usually is the note head that it applies to. When the note head is moved, the staccato dot moves along automatically.

A grob is often associated with a symbol, but some grobs do not print any symbols. They take care of grouping objects. For example, there is a separate grob that stacks staves vertically. The NoteCollision is also an abstract grob: it only moves around chords, but doesn't print anything.

Grobs have a properties: Scheme variables, that can be read and set. They have two types. Immutable variables define the default style and behavior. They are shared between many objects. They can be changed using `\override` and `\revert`.

Mutable properties are variables that are specific to one grob. Typically, lists of other objects, or results from computations are stored inmutable properties: every call to set-grob-property (or its C++ equivalent) sets a mutable property.

The properties `after-line-breaking` and `before-line-breaking` are dummies that are not user-serviceable.

##### User settable properties:

`X-extent` (pair of numbers)
  Hard coded extent in X direction.
`X-offset` (number)
  The horizontal amount that this object is moved relative to its X-parent
`Y-extent` (pair of numbers)
  See `X-extent`.
`Y-offset` (number)
  The vertical amount that this object is moved relative to its Y-parent
`after-line-breaking` (boolean)
  Dummy property, used to trigger callback for after-line-breaking
`before-line-breaking` (boolean)
  Dummy property, used to trigger a callback function.
`color` (list)
  The color of this grob.
`extra-X-extent` (pair of numbers)
  A grob is enlarged in X dimension by this much.
`extra-Y-extent` (pair of numbers)
  See `extra-Y-extent`.
`extra-offset` (pair of numbers)
  A pair representing an offset. This offset is added just before outputting the symbol, so the typesetting engine is completely oblivious to it.
`layer` (number)
  The output layer [0..2]: layers define the order of printing objects. Objects in lower layers are overprinted by objects in higher layers.
`minimum-X-extent` (pair of numbers)
  Minimum size of an object in X dimension, measured in staff space.
`minimum-Y-extent` (pair of numbers)
  See `minimum-Y-extent`.
`springs-and-rods` (boolean)
  Dummy variable for triggering spacing routines.
`transparent` (boolean)
  This makes the grob invisible.

##### Internal properties:

`axis-group-parent-X` (layout object)
  Containing X axis group
`axis-group-parent-Y` (layout object)
  Containing Y axis group
`cause` (any type)
  Any kind of causation objects (i.e. music, or perhaps translator) that was the cause for this grob.
`interfaces` (list)
  list of symbols indicating the interfaces supported by this object. Is initialized from the `meta` field.
`meta` (list)
  Contains meta information. It is an alist with the entries `name` and `interfaces`.
`staff-symbol` (layout object)
  the staff symbol grob that we're in.
`stencil` (unknown)
  The symbol to print.

This grob interface is used in the following graphical objects: Accidental, AccidentalPlacement, AccidentalSuggestion, Ambitus, AmbitusAccidental, AmbitusLine, AmbitusNoteHead, Arpeggio, BarLine, BarNumber, BassFigure, BassFigureAlignment, BassFigureBracket, BassFigureContinuation, BassFigureLine, Beam, BreakAlignGroup, BreakAlignment, BreathingSign, ChordName, Clef, ClusterSpanner, ClusterSpannerBeacon, CombineTextScript, Custos, DotColumn, Dots, DoublePercentRepeat, DoublePercentRepeatCounter, DynamicLineSpanner, DynamicText, DynamicTextSpanner, Fingering, Glissando, GridLine, GridPoint, Hairpin, HorizontalBracket, InstrumentName, KeyCancellation, KeySignature, LaissezVibrerTie, LaissezVibrerTieColumn, LedgerLineSpanner, LeftEdge, LigatureBracket, LyricExtender, LyricHyphen, LyricSpace, LyricText, MeasureGrouping, MelodyItem, MensuralLigature, MetronomeMark, MultiMeasureRest, MultiMeasureRestNumber, MultiMeasureRestText, NonMusicalPaperColumn, NoteCollision, NoteColumn, NoteHead, NoteName, NoteSpacing, OctavateEight, OttavaBracket, PaperColumn, ParenthesesItem, PercentRepeat, PercentRepeatCounter, PhrasingSlur, PianoPedalBracket, RehearsalMark, RepeatSlash, RepeatTie, RepeatTieColumn, Rest, RestCollision, Script, ScriptColumn, SeparatingGroupSpanner, SeparationItem, Slur, SostenutoPedal, SostenutoPedalLineSpanner, SpacingSpanner, SpanBar, StaffSpacing, StaffSymbol, StanzaNumber, Stem, StemTremolo, StringNumber, SustainPedal, SustainPedalLineSpanner, System, SystemStartBar, SystemStartBrace, SystemStartBracket, SystemStartSquare, TabNoteHead, TextScript, TextSpanner, Tie, TieColumn, TimeSignature, TrillPitchAccidental, TrillPitchGroup, TrillPitchHead, TrillSpanner, TupletBracket, TupletNumber, UnaCordaPedal, UnaCordaPedalLineSpanner, VaticanaLigature, VerticalAlignment, VerticalAxisGroup, VoiceFollower and VoltaBracket

This page is for LilyPond-2.8.8 (stable-branch).

Other languages: English.
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