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 <div class="chapter">
 <div class="titlepage"><div><div><h2 class="title">
 <a name="what-is-harfbuzz"></a>What is HarfBuzz?</h2></div></div></div>
 <div class="toc"><dl class="toc">
 <dt><span class="section"><a href="what-is-harfbuzz.html#what-is-text-shaping">What is text shaping?</a></span></dt>
 <dt><span class="section"><a href="why-do-i-need-a-shaping-engine.html">Why do I need a shaping engine?</a></span></dt>
 <dt><span class="section"><a href="ch01s03.html">What does HarfBuzz do?</a></span></dt>
 <dt><span class="section"><a href="what-harfbuzz-doesnt-do.html">What HarfBuzz doesn't do</a></span></dt>
 <dt><span class="section"><a href="why-is-it-called-harfbuzz.html">Why is it called HarfBuzz?</a></span></dt>
 </dl></div>
 <p>
     HarfBuzz is a <span class="emphasis"><em>text-shaping engine</em></span>. If you
     give HarfBuzz a font and a string containing a sequence of Unicode
     codepoints, HarfBuzz selects and positions the corresponding
     glyphs from the font, applying all of the necessary layout rules
     and font features. HarfBuzz then returns the string to you in the
     form that is correctly arranged for the language and writing
     system.
   </p>
 <p>
     HarfBuzz can properly shape all of the world's major writing
     systems. It runs on all major operating systems and software
     platforms and it supports the major font formats in use
     today.
   </p>
 <div class="section">
 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 <a name="what-is-text-shaping"></a>What is text shaping?</h2></div></div></div>
 <p>
       Text shaping is the process of translating a string of character
       codes (such as Unicode codepoints) into a properly arranged
       sequence of glyphs that can be rendered onto a screen or into
       final output form for inclusion in a document.
     </p>
 <p>
       The shaping process is dependent on the input string, the active
       font, the script (or writing system) that the string is in, and
       the language that the string is in.
     </p>
 <p>
       Modern software systems generally only deal with strings in the
       Unicode encoding scheme (although legacy systems and documents may
       involve other encodings).
     </p>
 <p>
       There are several font formats that a program might
       encounter, each of which has a set of standard text-shaping
       rules.
     </p>
 <p>The dominant format is <a class="ulink" href="http://www.microsoft.com/typography/otspec/" target="_top">OpenType</a>. The
     OpenType specification defines a series of <a class="ulink" href="https://github.com/n8willis/opentype-shaping-documents" target="_top">shaping models</a> for
     various scripts from around the world. These shaping models depend on
     the font incorporating certain features as
     <span class="emphasis"><em>lookups</em></span> in its <code class="literal">GSUB</code>
     and <code class="literal">GPOS</code> tables.
     </p>
 <p>
       Alternatively, OpenType fonts can include shaping features for
       the <a class="ulink" href="https://graphite.sil.org/" target="_top">Graphite</a> shaping model.
     </p>
 <p>
       TrueType fonts can also include OpenType shaping
       features. Alternatively, TrueType fonts can also include <a class="ulink" href="https://developer.apple.com/fonts/TrueType-Reference-Manual/RM09/AppendixF.html" target="_top">Apple
       Advanced Typography</a> (AAT) tables to implement shaping
       support. AAT fonts are generally only found on macOS and iOS systems.
     </p>
 <p>
       Text strings will usually be tagged with a script and language
       tag that provide the context needed to perform text shaping
       correctly.  The necessary <a class="ulink" href="https://docs.microsoft.com/en-us/typography/opentype/spec/scripttags" target="_top">script</a>
       and <a class="ulink" href="https://docs.microsoft.com/en-us/typography/opentype/spec/languagetags" target="_top">language</a>
       tags are defined by OpenType.
     </p>
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	<link rel="home" href="index.html" title="HarfBuzz Manual">
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	<link rel="prev" href="pt01.html" title="Part I. User's manual">
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	<div class="chapter">
	<div class="titlepage"><div><div><h2 class="title">
	<a name="what-is-harfbuzz"></a>What is HarfBuzz?</h2></div></div></div>
	<div class="toc"><dl class="toc">
	<dt><span class="section"><a href="what-is-harfbuzz.html#what-is-text-shaping">What is text shaping?</a></span></dt>
	<dt><span class="section"><a href="why-do-i-need-a-shaping-engine.html">Why do I need a shaping engine?</a></span></dt>
	<dt><span class="section"><a href="ch01s03.html">What does HarfBuzz do?</a></span></dt>
	<dt><span class="section"><a href="what-harfbuzz-doesnt-do.html">What HarfBuzz doesn't do</a></span></dt>
	<dt><span class="section"><a href="why-is-it-called-harfbuzz.html">Why is it called HarfBuzz?</a></span></dt>
	</dl></div>
	<p>
	HarfBuzz is a <span class="emphasis"><em>text-shaping engine</em></span>. If you
	give HarfBuzz a font and a string containing a sequence of Unicode
	codepoints, HarfBuzz selects and positions the corresponding
	glyphs from the font, applying all of the necessary layout rules
	and font features. HarfBuzz then returns the string to you in the
	form that is correctly arranged for the language and writing
	system.
	</p>
	<p>
	HarfBuzz can properly shape all of the world's major writing
	systems. It runs on all major operating systems and software
	platforms and it supports the major font formats in use
	today.
	</p>
	<div class="section">
	<div class="titlepage"><div><div><h2 class="title" style="clear: both">
	<a name="what-is-text-shaping"></a>What is text shaping?</h2></div></div></div>
	<p>
	Text shaping is the process of translating a string of character
	codes (such as Unicode codepoints) into a properly arranged
	sequence of glyphs that can be rendered onto a screen or into
	final output form for inclusion in a document.
	</p>
	<p>
	The shaping process is dependent on the input string, the active
	font, the script (or writing system) that the string is in, and
	the language that the string is in.
	</p>
	<p>
	Modern software systems generally only deal with strings in the
	Unicode encoding scheme (although legacy systems and documents may
	involve other encodings).
	</p>
	<p>
	There are several font formats that a program might
	encounter, each of which has a set of standard text-shaping
	rules.
	</p>
	<p>The dominant format is <a class="ulink" href="http://www.microsoft.com/typography/otspec/" target="_top">OpenType</a>. The
	OpenType specification defines a series of <a class="ulink" href="https://github.com/n8willis/opentype-shaping-documents" target="_top">shaping models</a> for
	various scripts from around the world. These shaping models depend on
	the font incorporating certain features as
	<span class="emphasis"><em>lookups</em></span> in its <code class="literal">GSUB</code>
	and <code class="literal">GPOS</code> tables.
	</p>
	<p>
	Alternatively, OpenType fonts can include shaping features for
	the <a class="ulink" href="https://graphite.sil.org/" target="_top">Graphite</a> shaping model.
	</p>
	<p>
	TrueType fonts can also include OpenType shaping
	features. Alternatively, TrueType fonts can also include <a class="ulink" href="https://developer.apple.com/fonts/TrueType-Reference-Manual/RM09/AppendixF.html" target="_top">Apple
	Advanced Typography</a> (AAT) tables to implement shaping
	support. AAT fonts are generally only found on macOS and iOS systems.
	</p>
	<p>
	Text strings will usually be tagged with a script and language
	tag that provide the context needed to perform text shaping
	correctly. The necessary <a class="ulink" href="https://docs.microsoft.com/en-us/typography/opentype/spec/scripttags" target="_top">script</a>
	and <a class="ulink" href="https://docs.microsoft.com/en-us/typography/opentype/spec/languagetags" target="_top">language</a>
	tags are defined by OpenType.
	</p>
	</div>
	</div>
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