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<title>Core Text integration: HarfBuzz Manual</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="integration-coretext"></a>Core Text integration</h2></div></div></div>
<p>
If your client program is running on macOS or iOS, HarfBuzz offers
an additional API that can help integrate with Apple's
Core Text engine and the underlying Core Graphics
framework. HarfBuzz does not attempt to offer the same
drop-in-replacement functionality for Core Text that it strives
for with Uniscribe on Windows, but you can still use HarfBuzz
to perform text shaping in native macOS and iOS applications.
</p>
<p>
Note, though, that if your interest is just in using fonts that
contain Apple Advanced Typography (AAT) features, then you do
not need to add Core Text integration. HarfBuzz natively
supports AAT features and will shape AAT fonts (on any platform)
automatically, without requiring additional work on your
part. This includes support for AAT-specific TrueType tables
such as <code class="literal">mort</code>, <code class="literal">morx</code>, and
<code class="literal">kerx</code>, which AAT fonts use instead of
<code class="literal">GSUB</code> and <code class="literal">GPOS</code>.
</p>
<p>
On a macOS or iOS system, the primary integration points offered
by HarfBuzz are for face objects and font objects.
</p>
<p>
The Apple APIs offer a pair of data structures that map well to
HarfBuzz's face and font objects. The Core Graphics API, which
is slightly lower-level than Core Text, provides
<a class="ulink" href="https://developer.apple.com/documentation/coregraphics/cgfontref" target="_top"><span class="type">CGFontRef</span></a>, which enables access to typeface
properties, but does not include size information. Core Text's
<a class="ulink" href="https://developer.apple.com/documentation/coretext/ctfont-q6r" target="_top"><span class="type">CTFontRef</span></a> is analagous to a HarfBuzz font object,
with all of the properties required to render text at a specific
size and configuration.
Consequently, a HarfBuzz <span class="type">hb_font_t</span> font object can
be hooked up to a Core Text <span class="type">CTFontRef</span>, and a HarfBuzz
<span class="type">hb_face_t</span> face object can be hooked up to a
<span class="type">CGFontRef</span>.
</p>
<p>
You can create a <span class="type">hb_face_t</span> from a
<span class="type">CGFontRef</span> by using the
<code class="function">hb_coretext_face_create()</code>. Subsequently,
you can retrieve the <span class="type">CGFontRef</span> from a
<span class="type">hb_face_t</span> with <code class="function">hb_coretext_face_get_cg_font()</code>.
</p>
<p>
Likewise, you create a <span class="type">hb_font_t</span> from a
<span class="type">CTFontRef</span> by calling
<code class="function">hb_coretext_font_create()</code>, and you can
fetch the associated <span class="type">CTFontRef</span> from a
<span class="type">hb_font_t</span> font object with
<code class="function">hb_coretext_face_get_ct_font()</code>.
</p>
<p>
HarfBuzz also offers a <code class="function">hb_font_set_ptem()</code>
that you an use to set the nominal point size on any
<span class="type">hb_font_t</span> font object. Core Text uses this value to
implement optical scaling.
</p>
<p>
When integrating your client code with Core Text, it is
important to recognize that Core Text <code class="literal">points</code>
are not typographic points (standardized at 72 per inch) as the
term is used elsewhere in OpenType. Instead, Core Text points
are CSS points, which are standardized at 96 per inch.
</p>
<p>
HarfBuzz's font functions take this distinction into account,
but it can be an easy detail to miss in cross-platform
code.
</p>
<p>
As a final note, you may notice a reference to an optional
<code class="literal">coretext</code> shaper back-end in the <a class="xref" href="building.html#configuration" title="Configuration options">the section called “Configuration options”</a> section of the HarfBuzz manual. This
option is not a Core Text-integration facility.
</p>
<p>
Instead, it is a internal code path used in the
<span class="command"><strong>hb-shape</strong></span> command-line utility, which hands
shaping functionality over to Core Text entirely, when run on a
macOS system. That allows testing HarfBuzz's native output
against the Core Text engine, for tracking compatibility and debugging.
</p>
<p>
Because this back-end is only used when testing HarfBuzz
functionality, it is disabled by default when building the
HarfBuzz binaries.
</p>
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