Modifying broken spanners

When a spanner crosses a line break or breaks, each piece inherits the attributes of the original spanner. Thus, ordinary tweaking of a broken spanner applies the same modifications to each of its segments. In the example below, overriding thickness affects the slur on either side of the line break.

\relative c'' {
  r2
  \once\override Slur.thickness = 10
  c8( d e f
  \break
  g8 f e d) r2
}

Independently modifying the appearance of individual pieces of a broken spanner is possible with the \alterBroken command. This command can produce either an \override or a \tweak of a spanner property.

The syntax for \alterBroken is

[-]\alterBroken property values target

The argument values is a list of values, one for each broken piece. If target is a grob name like Slur or Staff.PianoPedalBracket, the result is an \override of the specified grob type. If target is a music expression such as ‘(’ or ‘[’ the result is the same music expression with an appropriate tweak applied.

The leading hyphen must be used with the \tweak form. Do not add it when \alterBroken is used as an \override.

In its \override usage, \alterBroken may be prefaced by \once or \temporary and reverted by using \revert with property (see Intermediate substitution functions).

The following code applies an independent \override to each of the slur segments in the previous example:

\relative c'' {
  r2
  \alterBroken thickness #'(10 1) Slur
  c8( d e f
  \break
  g8 f e d) r2
}

The \alterBroken command may be used with any spanner object, including Tie, PhrasingSlur, Beam and TextSpanner. For example, an editor preparing a scholarly edition may wish to indicate the absence of part of a phrasing slur in a source by dashing only the segment which has been added. The following example illustrates how this can be done, in this case using the \tweak form of the command:

% The empty list is conveniently used below, because it is the
% default setting of dash-definition, resulting in a solid curve.
\relative {
  c''2-\alterBroken dash-definition #'(() ((0 1.0 0.4 0.75))) \(e
  \break
  g2 e\)
}

It is important to understand that \alterBroken sets each piece of a broken spanner to the corresponding value in values. When there are fewer values than pieces, any additional piece will be assigned the empty list. This may lead to undesired results if the layout property is not set to the empty list by default. In such cases, each segment should be assigned an appropriate value.

Known issues and warnings

Line breaks may occur in different places following changes in layout. Settings chosen for \alterBroken may be unsuitable for a spanner that is no longer broken or is split into more segments than before. Explicit use of \break can guard against this situation.

The \alterBroken command is ineffective for spanner properties accessed before line breaking such as direction.

See also

Extending LilyPond: Difficult tweaks.