item-interface

Grobs can be distinguished in their role in the horizontal spacing. Many grobs define constraints on the spacing by their sizes. For example, note heads, clefs, stems, and all other symbols with a fixed shape. These grobs form a subtype called Item.

Some items need special treatment for line breaking. For example, a clef is normally only printed at the start of a line (i.e. after a line break). To model this, `breakable' items (clef, key signature, bar lines, etc.) are copied twice. Then we have three versions of each breakable item: one version if there is no line break, one version that is printed before the line break (at the end of a system), one version that is printed after the line break.

Whether these versions are visible and take up space, is determined by the outcome of the break-visibility. This grob property is a function taking a direction (-1, 0 or 1) as argument. It returns a cons of booleans, signifying whether this grob should be transparent and have no extent.

The following variables for break-visibility are predefined:

                grob will show:   before  no     after
                                  break   break  break
       all-invisible              no      no     no
       begin-of-line-visible      no      no     yes
       end-of-line-visible        yes     no     no
       all-visible                yes     yes    yes
       begin-of-line-invisible    yes     yes    no
       end-of-line-invisible      no      yes    yes
       center-invisible           yes      no    yes

User settable properties:

break-visibility (vector)

A vector of 3 booleans, #(end-of-line unbroken begin-of-line). #t means visible, #f means killed.

no-spacing-rods (boolean)

Items with this property do not cause spacing constraints.

non-musical (boolean)

True if the grob belongs in a NonMusicalPaperColumn.

This grob interface is used in the following graphical objects: Accidental, AccidentalPlacement, AccidentalSuggestion, Ambitus, AmbitusAccidental, AmbitusLine, AmbitusNoteHead, Arpeggio, BalloonTextItem, BarLine, BarNumber, BassFigure, BassFigureBracket, BreakAlignGroup, BreakAlignment, BreathingSign, ChordName, Clef, ClusterSpannerBeacon, CombineTextScript, Custos, DotColumn, Dots, DoublePercentRepeat, DoublePercentRepeatCounter, DynamicText, Fingering, FretBoard, GridLine, GridPoint, InstrumentSwitch, KeyCancellation, KeySignature, LaissezVibrerTie, LaissezVibrerTieColumn, LeftEdge, LyricText, MelodyItem, MetronomeMark, NonMusicalPaperColumn, NoteCollision, NoteColumn, NoteHead, NoteName, NoteSpacing, OctavateEight, PaperColumn, ParenthesesItem, RehearsalMark, RepeatSlash, RepeatTie, RepeatTieColumn, Rest, RestCollision, Script, ScriptColumn, ScriptRow, SeparationItem, SostenutoPedal, SpanBar, StaffSpacing, StanzaNumber, Stem, StemTremolo, StringNumber, StrokeFinger, SustainPedal, TabNoteHead, TextScript, TimeSignature, TrillPitchAccidental, TrillPitchGroup, TrillPitchHead and UnaCordaPedal