5.1.1 Objects and interfaces (LilyPond Learning Manual)

#### 5.1.1 Objects and interfaces

Tweaking involves modifying the internal operation and structures of the LilyPond program, so we must first introduce some terms which are used to describe those internal operations and structures.

The term Object is a generic term used to refer to the multitude of internal structures built by LilyPond during the processing of an input file. So when a command like `\new Staff` is encountered a new object of type `Staff` is constructed. That `Staff` object then holds all the properties associated with that particular staff, for example, its name and its key signature, together with details of the engravers which have been assigned to operate within that staff’s context. Similarly, there are objects to hold the properties of all other contexts, such as `Voice` objects, `Score` objects, `Lyrics` objects, as well as objects to represent all notational elements such as bar lines, note heads, ties, dynamics, etc. Every object has its own set of property values.

Some types of object are given special names. Objects that represent items of notation on the printed output such as note heads, stems, slurs, ties, fingering, clefs, etc are called ‘Layout objects’, often known as ‘Graphical Objects’, or grobs for short. These are still objects in the generic sense above, and so they too all have properties associated with them, such as their position, size, color, etc.

Some layout objects are still more specialized. Phrasing slurs, crescendo hairpins, ottava marks, and many other grobs are not localized in a single place – they have a starting point, an ending point, and maybe other properties concerned with their shape. Objects with an extended shape like these are called spanners.

Spanners cannot be tweaked after their creation. This includes both `StaffSymbol` and `LedgerLineSpanner`, which continue throughout the score, except if they are terminated by the `\stopStaff` command and then recreated using `\startStaff` command.

What is more, there are ‘abstract’ grobs which do not print anything of their own, but rather collect, position and manage other grobs. Common examples for this are `DynamicLineSpanner`, `BreakAlignment`, `NoteColumn`, `VerticalAxisGroup`, or `NonMusicalPaperColumn`. We will see how some of these are used later.

It remains to explain what interfaces are. Many objects, even though they are quite different, share common features which need to be processed in the same way. For example, all grobs have a color, a size, a position, etc, and all these properties are processed in the same way during LilyPond’s interpretation of the input file. To simplify these internal operations these common actions and properties are grouped together in an object called a `grob-interface`. There are many other groupings of common properties like this, each one given a name ending in `interface`. In total there are over 100 such interfaces. We shall see later why this is of interest and use to the user.

These, then, are the main terms relating to objects which we shall use in this chapter.

#### LilyPond Learning Manual v2.26.0 (stable-branch).

- 1 Installing
  - 1.1 Graphical setup
  - 1.2 Command line setup
- 2 Tutorial
  - 2.1 Compiling a file
  - 2.2 How to write input files
    - 2.2.1 Input characters
    - 2.2.2 Simple notation
      - Pitches
      - Durations (rhythms)
      - Rests
      - Time signature
      - Tempo marks
      - Clef
      - All together
    - 2.2.3 Working on input files
  - 2.3 Dealing with errors
  - 2.4 How to read the manuals
    - 2.4.1 Omitted material
    - 2.4.2 Clickable examples
    - 2.4.3 Overview of manuals
- 3 Common notation
  - 3.1 Single-staff notation
    - 3.1.1 Bar lines and bar checks
      - Bar lines
      - Bar checks
    - 3.1.2 Pitches and key signatures
      - Pitch alterations
      - Key signatures
      - Warning: key signatures and pitches
    - 3.1.3 Ties and slurs
      - Ties
      - Slurs
      - Phrasing slurs
      - Warnings: slurs vs. ties
    - 3.1.4 Articulations and dynamics
      - Articulations
      - Fingerings
      - Dynamics
    - 3.1.5 Adding text
    - 3.1.6 Automatic and manual beams
    - 3.1.7 Advanced rhythmic commands
      - Partial measure
      - Tuplets
      - Grace notes
  - 3.2 Multiple notes at once
    - 3.2.1 Music expressions explained
      - Analogy: mathematical expressions
      - Simultaneous music expressions: multiple staves
      - Simultaneous music expressions: single-staff
    - 3.2.2 Multiple staves
    - 3.2.3 Staff groups
    - 3.2.4 Combining notes into chords
    - 3.2.5 Single-staff polyphony
  - 3.3 Songs
    - 3.3.1 Setting simple songs
    - 3.3.2 Aligning lyrics to a melody
    - 3.3.3 Lyrics to multiple staves
  - 3.4 Final touches
    - 3.4.1 Organizing pieces with variables
    - 3.4.2 Adding titles
    - 3.4.3 Absolute note names
    - 3.4.4 After the tutorial
- 4 Fundamental concepts
  - 4.1 How LilyPond input files work
    - 4.1.1 Introduction to the LilyPond file structure
    - 4.1.2 A score is a (single) compound musical expression
    - 4.1.3 Nesting music expressions
    - 4.1.4 Structure of a note entry
    - 4.1.5 On the un-nestedness of brackets and ties
  - 4.2 Voices contain music
    - 4.2.1 I’m hearing voices
    - 4.2.2 Explicitly instantiating voices
    - 4.2.3 Voices and vocals
  - 4.3 Contexts and engravers
    - 4.3.1 Contexts explained
    - 4.3.2 Creating contexts
    - 4.3.3 Engravers explained
    - 4.3.4 Modifying context properties
    - 4.3.5 Adding and removing engravers
  - 4.4 Extending the templates
    - 4.4.1 Soprano and cello
    - 4.4.2 Four-part SATB vocal score
    - 4.4.3 Building a score from scratch
    - 4.4.4 Saving typing with variables and functions
    - 4.4.5 Scores and parts
- 5 Tweaking output
  - 5.1 Tweaking basics
    - 5.1.1 Objects and interfaces
    - 5.1.2 Naming conventions of objects and properties
    - 5.1.3 Tweaking methods
      - The `\override` command
      - The `\revert` command
      - The `\once` prefix
      - The `\tweak` and `\offset` commands
      - The `\single` prefix
  - 5.2 The Internals Reference manual
    - 5.2.1 Properties of layout objects
    - 5.2.2 Properties found in interfaces
    - 5.2.3 Types of properties
  - 5.3 Appearance of objects
    - 5.3.1 Visibility and color of objects
      - The `stencil` property
      - The `break-visibility` property
      - The `transparent` property
      - The `color` property
    - 5.3.2 Size of objects
    - 5.3.3 Length and thickness of objects
  - 5.4 Offsets and alignments
  - 5.5 Placement of objects
    - 5.5.1 Automatic behavior
    - 5.5.2 Within-staff objects
      - The `direction` property
      - Fingering
    - 5.5.3 Outside-staff objects
      - The `outside-staff-priority` property
      - The `\textLengthOn` command
      - Dynamics placement
      - Grob sizing
  - 5.6 Vertical spacing
  - 5.7 Collisions of objects
    - 5.7.1 Moving objects
    - 5.7.2 Fixing overlapping notation
      - The `padding` property
      - The `right-padding` property
      - The `staff-padding` property
      - The `self-alignment-X` property
      - The `staff-position` property
      - The `extra-offset` property
      - The `positions` property
      - The `force-hshift` property
    - 5.7.3 Real music example
  - 5.8 Further tweaking
    - 5.8.1 Other uses for tweaks
      - Tying notes across voices
      - Simulating a fermata in MIDI
    - 5.8.2 Using variables for layout adjustments
    - 5.8.3 Style sheets
    - 5.8.4 Other sources of information
    - 5.8.5 Advanced tweaks with Scheme
- Appendix A Templates
  - A.1 Built-in templates
    - A.1.1 SATB template
    - A.1.2 SSAATTBB template
  - A.2 Single staff templates
    - A.2.1 Notes only
    - A.2.2 Notes and lyrics
    - A.2.3 Notes and chords
    - A.2.4 Notes, lyrics, and chords
  - A.3 Piano templates
    - A.3.1 Solo piano
    - A.3.2 Piano and melody with lyrics
    - A.3.3 Piano-centered lyrics
  - A.4 String quartet templates
    - A.4.1 String quartet
    - A.4.2 String quartet parts
  - A.5 Vocal ensembles templates
    - A.5.1 SATB vocal score
    - A.5.2 SATB vocal score and automatic piano reduction
    - A.5.3 SATB with aligned contexts
    - A.5.4 SATB on four staves
    - A.5.5 Solo verse and two-part refrain
    - A.5.6 Hymn tunes
    - A.5.7 Psalms
  - A.6 Orchestral templates
    - A.6.1 Orchestra, choir and piano
  - A.7 Ancient notation templates
    - A.7.1 Transcription of mensural music
    - A.7.2 Gregorian transcription template
  - A.8 Other templates
    - A.8.1 Jazz combo
- Appendix B GNU Free Documentation License
- Appendix C Index