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<a name="Difficult-tweaks"></a>
Previous: <a rel="previous" accesskey="p" href="Using-Scheme-code-instead-of-_005ctweak.es.html#Using-Scheme-code-instead-of-_005ctweak">Using Scheme code instead of \tweak</a>,
Up: <a rel="up" accesskey="u" href="TODO-moved-into-scheme.es.html#TODO-moved-into-scheme">TODO moved into scheme</a>
<hr>
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<h4 class="subsection">6.7.2 Difficult tweaks</h4>
<p>There are a few classes of difficult adjustments.
<ul>
<li>One type of difficult adjustment is the appearance of spanner objects,
such as slur and tie. Initially, only one of these objects is created,
and they can be adjusted with the normal mechanism. However, in some
cases the spanners cross line breaks. If this happens, these objects
are cloned. A separate object is created for every system that it is
in. These are clones of the original object and inherit all
properties, including <code>\override</code>s.
<p>In other words, an <code>\override</code> always affects all pieces of a
broken spanner. To change only one part of a spanner at a line break,
it is necessary to hook into the formatting process. The
<code>after-line-breaking</code> callback contains the Scheme procedure that
is called after the line breaks have been determined, and layout
objects have been split over different systems.
<p>In the following example, we define a procedure
<code>my-callback</code>. This procedure
<ul>
<li>determines if we have been split across line breaks
<li>if yes, retrieves all the split objects
<li>checks if we are the last of the split objects
<li>if yes, it sets <code>extra-offset</code>.
</ul>
<p>This procedure is installed into <a name="index-Tie-2835"></a><a href="../lilypond-internals/Tie.es.html#Tie">Tie</a>, so the last part
of the broken tie is translated up.
<blockquote>
<pre class="verbatim">
#(define (my-callback grob)
(let* (
; have we been split?
(orig (ly:grob-original grob))
; if yes, get the split pieces (our siblings)
(siblings (if (ly:grob? orig)
(ly:spanner-broken-into orig) '() )))
(if (and (>= (length siblings) 2)
(eq? (car (last-pair siblings)) grob))
(ly:grob-set-property! grob 'extra-offset '(-2 . 5)))))
\relative c'' {
\override Tie #'after-line-breaking =
#my-callback
c1 ~ \break c2 ~ c
}
</pre>
<p>
<a href="../c3/lily-92ba8123.ly">
<img align="middle"
border="0" src="../c3/lily-92ba8123.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">When applying this trick, the new <code>after-line-breaking</code> callback
should also call the old one <code>after-line-breaking</code>, if there is
one. For example, if using this with <code>Hairpin</code>,
<code>ly:hairpin::after-line-breaking</code> should also be called.
<li>Some objects cannot be changed with <code>\override</code> for
technical reasons. Examples of those are <code>NonMusicalPaperColumn</code>
and <code>PaperColumn</code>. They can be changed with the
<code>\overrideProperty</code> function, which works similar to <code>\once
\override</code>, but uses a different syntax.
<pre class="example"> \overrideProperty
#"Score.NonMusicalPaperColumn" % Grob name
#'line-break-system-details % Property name
#'((next-padding . 20)) % Value
</pre>
<p>Note, however, that <code>\override</code>, applied to
<code>NoteMusicalPaperColumn</code> and <code>PaperColumn</code>, still works as
expected within <code>\context</code> blocks.
</ul>
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<p>
Previous: <a rel="previous" accesskey="p" href="Using-Scheme-code-instead-of-_005ctweak.es.html#Using-Scheme-code-instead-of-_005ctweak">Using Scheme code instead of weak</a>,
Up: <a rel="up" accesskey="u" href="TODO-moved-into-scheme.es.html#TODO-moved-into-scheme">TODO moved into scheme</a>
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<P>
Otros idiomas: <a href="Difficult-tweaks.fr.html">français</a>.
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