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<a name="What-symbols-to-engrave%3f"></a>
<a name="What-symbols-to-engrave_003f"></a>
Next: <a rel="next" accesskey="n" href="Music-representation.html#Music-representation">Music representation</a>,
Previous: <a rel="previous" accesskey="p" href="Automated-engraving.html#Automated-engraving">Automated engraving</a>,
Up: <a rel="up" accesskey="u" href="Background.html#Background">Background</a>
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<h4 class="unnumberedsubsec">What symbols to engrave?</h4>
<p><a name="index-engraving-11"></a><a name="index-typography-12"></a>
The formatting process decides where to place symbols. However,
this can only be done once it is decided <em>what</em> symbols
should be printed, in other words what notation to use.
<p>Common music notation is a system of recording music that has
evolved over the past 1000 years. The form that is now in common
use dates from the early renaissance. Although the basic form
(i.e., note heads on a 5-line staff) has not changed, the details
still evolve to express the innovations of contemporary notation.
Hence, it encompasses some 500 years of music. Its applications
range from monophonic melodies to monstrous counterpoints for
large orchestras.
<p>How can we get a grip on such a many-headed beast, and force it
into the confines of a computer program? Our solution is to break
up the problem of notation (as opposed to engraving, i.e.,
typography) into digestible and programmable chunks: every type of
symbol is handled by a separate module, a so-called plug-in. Each
plug-in is completely modular and independent, so each can be
developed and improved separately. Such plug-ins are called
<code>engraver</code>s, by analogy with craftsmen who translate musical
ideas to graphic symbols.
<p>In the following example, we see how we start out with a plug-in
for note heads, the <code>Note_heads_engraver</code>.
<blockquote>
<p>
<a href="../ab/lily-b4a43b4c.ly">
<img align="middle"
border="0" src="../ab/lily-b4a43b4c.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">Then a <code>Staff_symbol_engraver</code> adds the staff
<blockquote>
<p>
<a href="../4f/lily-d3521339.ly">
<img align="middle"
border="0" src="../4f/lily-d3521339.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">the <code>Clef_engraver</code> defines a reference point for the staff
<blockquote>
<p>
<a href="../aa/lily-09f3f79c.ly">
<img align="middle"
border="0" src="../aa/lily-09f3f79c.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">and the <code>Stem_engraver</code> adds stems.
<blockquote>
<p>
<a href="../b6/lily-678a89f6.ly">
<img align="middle"
border="0" src="../b6/lily-678a89f6.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p class="noindent">The <code>Stem_engraver</code> is notified of any note head coming
along. Every time one (or more, for a chord) note head is seen, a
stem object is created and connected to the note head. By adding
engravers for beams, slurs, accents, accidentals, bar lines, time
signature, and key signature, we get a complete piece of notation.
<blockquote>
<p>
<a href="../21/lily-46f41737.ly">
<img align="middle"
border="0" src="../21/lily-46f41737.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>This system works well for monophonic music, but what about
polyphony? In polyphonic notation, many voices can share a staff.
<blockquote>
<p>
<a href="../f3/lily-dec1d271.ly">
<img align="middle"
border="0" src="../f3/lily-dec1d271.png" alt="[image of music]">
</a>
</p>
</blockquote>
<p>In this situation, the accidentals and staff are shared, but the
stems, slurs, beams, etc., are private to each voice. Hence,
engravers should be grouped. The engravers for note heads, stems,
slurs, etc., go into a group called ‘Voice context,’ while the
engravers for key, accidental, bar, etc., go into a group called
‘Staff context.’ In the case of polyphony, a single Staff
context contains more than one Voice context. Similarly, multiple
Staff contexts can be put into a single Score context. The Score
context is the top level notation context.
<p class="noindent">
<h5 class="subsubheading">See also</h5>
<p class="indent">
<p>Internals Reference: <a name="index-Contexts-13"></a><a href="../lilypond-internals/Contexts.html#Contexts">Contexts</a>.
<blockquote>
<p>
<a href="../8e/lily-558a01df.ly">
<img align="middle"
border="0" src="../8e/lily-558a01df.png" alt="[image of music]">
</a>
</p>
</blockquote>
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Previous: <a rel="previous" accesskey="p" href="Automated-engraving.html#Automated-engraving">Automated engraving</a>,
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