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24 <a name="integration-coretext"></a>Core Text integration</h2></div></div></div>
26 If your client program is running on macOS or iOS, HarfBuzz offers
27 an additional API that can help integrate with Apple's
28 Core Text engine and the underlying Core Graphics
29 framework. HarfBuzz does not attempt to offer the same
30 drop-in-replacement functionality for Core Text that it strives
31 for with Uniscribe on Windows, but you can still use HarfBuzz
32 to perform text shaping in native macOS and iOS applications.
35 Note, though, that if your interest is just in using fonts that
36 contain Apple Advanced Typography (AAT) features, then you do
37 not need to add Core Text integration. HarfBuzz natively
38 supports AAT features and will shape AAT fonts (on any platform)
39 automatically, without requiring additional work on your
40 part. This includes support for AAT-specific TrueType tables
41 such as <code class="literal">mort</code>, <code class="literal">morx</code>, and
42 <code class="literal">kerx</code>, which AAT fonts use instead of
43 <code class="literal">GSUB</code> and <code class="literal">GPOS</code>.
46 On a macOS or iOS system, the primary integration points offered
47 by HarfBuzz are for face objects and font objects.
50 The Apple APIs offer a pair of data structures that map well to
51 HarfBuzz's face and font objects. The Core Graphics API, which
52 is slightly lower-level than Core Text, provides
53 <a class="ulink" href="https://developer.apple.com/documentation/coregraphics/cgfontref" target="_top"><span class="type">CGFontRef</span></a>, which enables access to typeface
54 properties, but does not include size information. Core Text's
55 <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,
56 with all of the properties required to render text at a specific
57 size and configuration.
58 Consequently, a HarfBuzz <span class="type">hb_font_t</span> font object can
59 be hooked up to a Core Text <span class="type">CTFontRef</span>, and a HarfBuzz
60 <span class="type">hb_face_t</span> face object can be hooked up to a
61 <span class="type">CGFontRef</span>.
64 You can create a <span class="type">hb_face_t</span> from a
65 <span class="type">CGFontRef</span> by using the
66 <code class="function">hb_coretext_face_create()</code>. Subsequently,
67 you can retrieve the <span class="type">CGFontRef</span> from a
68 <span class="type">hb_face_t</span> with <code class="function">hb_coretext_face_get_cg_font()</code>.
71 Likewise, you create a <span class="type">hb_font_t</span> from a
72 <span class="type">CTFontRef</span> by calling
73 <code class="function">hb_coretext_font_create()</code>, and you can
74 fetch the associated <span class="type">CTFontRef</span> from a
75 <span class="type">hb_font_t</span> font object with
76 <code class="function">hb_coretext_face_get_ct_font()</code>.
79 HarfBuzz also offers a <code class="function">hb_font_set_ptem()</code>
80 that you an use to set the nominal point size on any
81 <span class="type">hb_font_t</span> font object. Core Text uses this value to
82 implement optical scaling.
85 When integrating your client code with Core Text, it is
86 important to recognize that Core Text <code class="literal">points</code>
87 are not typographic points (standardized at 72 per inch) as the
88 term is used elsewhere in OpenType. Instead, Core Text points
89 are CSS points, which are standardized at 96 per inch.
92 HarfBuzz's font functions take this distinction into account,
93 but it can be an easy detail to miss in cross-platform
97 As a final note, you may notice a reference to an optional
98 <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
99 option is not a Core Text-integration facility.
102 Instead, it is a internal code path used in the
103 <span class="command"><strong>hb-shape</strong></span> command-line utility, which hands
104 shaping functionality over to Core Text entirely, when run on a
105 macOS system. That allows testing HarfBuzz's native output
106 against the Core Text engine, for tracking compatibility and debugging.
109 Because this back-end is only used when testing HarfBuzz
110 functionality, it is disabled by default when building the
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