The \override command (LilyPond 学习手册)

#### The `\override` command

We have already met the commands `\set` and `\with`, used to change the properties of contexts and to remove and add engravers, in Modifying context properties, and Adding and removing engravers. We must now introduce some more important commands.

The command to change the properties of layout objects is `\override`. Because this command has to modify internal properties deep within LilyPond its syntax is not as simple as the commands you have used so far. It needs to know precisely which property of which object in which context has to be modified, and what its new value is to be. Let’s see how this is done.

The general syntax of this command is:

    \override Context.LayoutObject.layout-property = value

This sets the property with the name layout-property of the layout object with the name LayoutObject, which is a member of the Context context, to the value value.

The Context may be omitted (and usually is) when the required context is unambiguously implied and is one of lowest level contexts, i.e., `Voice`, `ChordNames` or `Lyrics`, and we shall omit it in many of the following examples. We shall see later when it must be specified.

Later sections deal comprehensively with properties and their values, see Types of properties. But in this section we shall use just a few simple properties and values which are easily understood in order to illustrate the format and use of these commands.

LilyPond’s primary expressions are musical items like notes and durations, as well as strings and markups. More specific expressions like symbols and lists are processed in ‘Scheme mode’, which is invoked by prefixing the value with ‘`#`’. A special case are numbers, which must be prefixed with ‘`#`’ only if used as arguments to a markup function (i.e., within `\markup`).2

For more information about Scheme mode, see LilyPond Scheme syntax.

`\override` is the most common command used in tweaking, and most of the rest of this chapter will be directed to presenting examples of how it is used. Here is a simple example to change the color of the note head:

>     \relative {
>       c'4 d
>       \override NoteHead.color = "red"
>       e4 f |
>       \override NoteHead.color = "green"
>       g4 a b c |
>     }

#### Footnotes

##### (2)

Note, however, that for LilyPond a number must start with a digit or a minus sign followed by a digit if not in Scheme mode. In other words, ‘`0.2`’ or ‘`-0.2`’ are valid numbers, while ‘`.2`’ or ‘`-.2`’ are not. If really necessary you can write ‘`#.2`’ or ‘`#-.2`’ instead – Scheme supports a much broader range of number representations.

#### LilyPond 学习手册 v2.26.0 (stable-branch).

- 1 Installing
  - 1.1 Graphical setup
  - 1.2 Command line setup
- 2 教程
  - 2.1 编译文件
  - 2.2 如何写输入文件
    - 2.2.1 简单记谱法
      - 音高
      - 时值 (节奏)
      - 休止符
      - 拍子记号
      - 速度记号
      - 谱号（音部记号）
      - 所有的都放在一起
    - 2.2.2 处理输入文件
  - 2.3 处理报错
    - 2.3.1 一般解决问题的方法
    - 2.3.2 常见的错误
  - 2.4 如何阅读教程
    - 2.4.1 忽略掉的内容
    - 2.4.2 可以点开的例子
    - 2.4.3 手册概览
- 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