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 <div class="section">
 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 <a name="a-clustering-example-for-levels-0-and-1"></a>A clustering example for levels 0 and 1</h2></div></div></div>
 <p>
       The basic shaping operations affect clusters in a predictable
       manner when using level 0 or level 1:
     </p>
 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 <li class="listitem"><p>
 	  When two or more clusters <span class="emphasis"><em>merge</em></span>, the
 	  resulting merged cluster takes as its cluster value the
 	  <span class="emphasis"><em>minimum</em></span> of the incoming cluster values.
 	</p></li>
 <li class="listitem"><p>
 	  When a cluster <span class="emphasis"><em>decomposes</em></span>, all of the
 	  resulting child clusters inherit as their cluster value the
 	  cluster value of the parent cluster.
 	</p></li>
 <li class="listitem"><p>
 	  When a character is <span class="emphasis"><em>reordered</em></span>, the
 	  reordered character and all clusters that the character
 	  moves past as part of the reordering are merged into one cluster.
 	</p></li>
 </ul></div>
 <p>
       The functionality, guarantees, and benefits of level 0 and level
       1 behavior can be seen with some examples. First, let us examine
       what happens with cluster values when shaping involves cluster
       merging with ligatures and decomposition.
     </p>
 <p>
       Let's say we start with the following character sequence (top row) and
       initial cluster values (bottom row):
     </p>
 <pre class="programlisting">
       A,B,C,D,E
       0,1,2,3,4
     </pre>
 <p>
       During shaping, HarfBuzz maps these characters to glyphs from
       the font. For simplicity, let us assume that each character maps
       to the corresponding, identical-looking glyph:
     </p>
 <pre class="programlisting">
       A,B,C,D,E
       0,1,2,3,4
     </pre>
 <p>
       Now if, for example, <code class="literal">B</code> and <code class="literal">C</code>
       form a ligature, then the clusters to which they belong
       "merge". This merged cluster takes for its cluster
       value the minimum of all the cluster values of the clusters that
       went in to the ligature. In this case, we get:
     </p>
 <pre class="programlisting">
       A,BC,D,E
       0,1 ,3,4
     </pre>
 <p>
       because 1 is the minimum of the set {1,2}, which were the
       cluster values of <code class="literal">B</code> and
       <code class="literal">C</code>.
     </p>
 <p>
       Next, let us say that the <code class="literal">BC</code> ligature glyph
       decomposes into three components, and <code class="literal">D</code> also
       decomposes into two components. Whenever a cluster decomposes,
       its components each inherit the cluster value of their parent:
     </p>
 <pre class="programlisting">
       A,BC0,BC1,BC2,D0,D1,E
       0,1  ,1  ,1  ,3 ,3 ,4
     </pre>
 <p>
       Next, if <code class="literal">BC2</code> and <code class="literal">D0</code> form a
       ligature, then their clusters (cluster values 1 and 3) merge into
       <code class="literal">min(1,3) = 1</code>:
     </p>
 <pre class="programlisting">
       A,BC0,BC1,BC2D0,D1,E
       0,1  ,1  ,1    ,1 ,4
     </pre>
 <p>
       Note that the entirety of cluster 3 merges into cluster 1, not
       just the <code class="literal">D0</code> glyph. This reflects the fact
       that the cluster <span class="emphasis"><em>must</em></span> be treated as an
       indivisible unit.
     </p>
 <p>
       At this point, cluster 1 means: the character sequence
       <code class="literal">BCD</code> is represented by glyphs
       <code class="literal">BC0,BC1,BC2D0,D1</code> and cannot be broken down any
       further.
     </p>
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	<div class="section">
	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
	<a name="a-clustering-example-for-levels-0-and-1"></a>A clustering example for levels 0 and 1</h2></div></div></div>
	<p>
	The basic shaping operations affect clusters in a predictable
	manner when using level 0 or level 1:
	</p>
	<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
	<li class="listitem"><p>
	When two or more clusters <span class="emphasis"><em>merge</em></span>, the
	resulting merged cluster takes as its cluster value the
	<span class="emphasis"><em>minimum</em></span> of the incoming cluster values.
	</p></li>
	<li class="listitem"><p>
	When a cluster <span class="emphasis"><em>decomposes</em></span>, all of the
	resulting child clusters inherit as their cluster value the
	cluster value of the parent cluster.
	</p></li>
	<li class="listitem"><p>
	When a character is <span class="emphasis"><em>reordered</em></span>, the
	reordered character and all clusters that the character
	moves past as part of the reordering are merged into one cluster.
	</p></li>
	</ul></div>
	<p>
	The functionality, guarantees, and benefits of level 0 and level
	1 behavior can be seen with some examples. First, let us examine
	what happens with cluster values when shaping involves cluster
	merging with ligatures and decomposition.
	</p>
	<p>
	Let's say we start with the following character sequence (top row) and
	initial cluster values (bottom row):
	</p>
	<pre class="programlisting">
	A,B,C,D,E
	0,1,2,3,4
	</pre>
	<p>
	During shaping, HarfBuzz maps these characters to glyphs from
	the font. For simplicity, let us assume that each character maps
	to the corresponding, identical-looking glyph:
	</p>
	<pre class="programlisting">
	A,B,C,D,E
	0,1,2,3,4
	</pre>
	<p>
	Now if, for example, <code class="literal">B</code> and <code class="literal">C</code>
	form a ligature, then the clusters to which they belong
	"merge". This merged cluster takes for its cluster
	value the minimum of all the cluster values of the clusters that
	went in to the ligature. In this case, we get:
	</p>
	<pre class="programlisting">
	A,BC,D,E
	0,1 ,3,4
	</pre>
	<p>
	because 1 is the minimum of the set {1,2}, which were the
	cluster values of <code class="literal">B</code> and
	<code class="literal">C</code>.
	</p>
	<p>
	Next, let us say that the <code class="literal">BC</code> ligature glyph
	decomposes into three components, and <code class="literal">D</code> also
	decomposes into two components. Whenever a cluster decomposes,
	its components each inherit the cluster value of their parent:
	</p>
	<pre class="programlisting">
	A,BC0,BC1,BC2,D0,D1,E
	0,1 ,1 ,1 ,3 ,3 ,4
	</pre>
	<p>
	Next, if <code class="literal">BC2</code> and <code class="literal">D0</code> form a
	ligature, then their clusters (cluster values 1 and 3) merge into
	<code class="literal">min(1,3) = 1</code>:
	</p>
	<pre class="programlisting">
	A,BC0,BC1,BC2D0,D1,E
	0,1 ,1 ,1 ,1 ,4
	</pre>
	<p>
	Note that the entirety of cluster 3 merges into cluster 1, not
	just the <code class="literal">D0</code> glyph. This reflects the fact
	that the cluster <span class="emphasis"><em>must</em></span> be treated as an
	indivisible unit.
	</p>
	<p>
	At this point, cluster 1 means: the character sequence
	<code class="literal">BCD</code> is represented by glyphs
	<code class="literal">BC0,BC1,BC2D0,D1</code> and cannot be broken down any
	further.
	</p>
	</div>
	<div class="footer">
	<hr>Generated by GTK-Doc V1.25</div>
	</body>
	</html>