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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="object-model-object-types"></a>Objects in HarfBuzz</h2></div></div></div>
<p>
<span class="emphasis"><em>Object types:</em></span> Opaque struct types are used
for what HarfBuzz loosely calls "objects." This doesn’t have
much to do with the terminology from object-oriented programming
(OOP), although some of the concepts are similar.
</p>
<p>
In HarfBuzz, all object types provide certain
lifecycle-management APIs. Objects are reference-counted, and
constructed with various <code class="function">create()</code> methods, referenced via
<code class="function">reference()</code> and dereferenced using
<code class="function">destroy()</code>.
</p>
<p>
For example,
the <code class="literal">hb_buffer_t</code> object has
<code class="function">hb_buffer_create()</code> as its constructor,
<code class="function">hb_buffer_reference()</code> to reference, and
<code class="function">hb_buffer_destroy()</code> to dereference.
</p>
<p>
After construction, each object's properties are accessible only
through the setter and getter functions described in the API
Reference manual.
</p>
<p>
Note that many object types can be marked as read-only or immutable,
facilitating their use in multi-threaded environments.
</p>
<p>
Key object types provided by HarfBuzz include:
</p>
<div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: disc; ">
<li class="listitem"><p>
<span class="emphasis"><em>blobs</em></span>, which act as low-level wrappers around binary
data. Blobs are typically used to hold the contents of a
binary font file.
</p></li>
<li class="listitem"><p>
<span class="emphasis"><em>faces</em></span>, which represent typefaces from a
font file, but without specific parameters (such as size) set.
</p></li>
<li class="listitem"><p>
<span class="emphasis"><em>fonts</em></span>, which represent instances of a
face with all of their parameters specified.
</p></li>
<li class="listitem"><p>
<span class="emphasis"><em>buffers</em></span>, which hold Unicode code points
for characters (before shaping) and the shaped glyph output
(after shaping).
</p></li>
<li class="listitem"><p>
<span class="emphasis"><em>shape plans</em></span>, which store the settings
that HarfBuzz will use when shaping a particular text
segment. Shape plans are not generally used by client
programs directly, but as we will see in a later chapter,
they are still valuable to understand.
</p></li>
</ul></div>
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