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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>FreeType integration: HarfBuzz Manual</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="HarfBuzz Manual"> <link rel="up" href="integration.html" title="Platform Integration Guide"> <link rel="prev" href="integration.html" title="Platform Integration Guide"> <link rel="next" href="integration-uniscribe.html" title="Uniscribe integration"> <meta name="generator" content="GTK-Doc V1.32 (XML mode)"> <link rel="stylesheet" href="style.css" type="text/css"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="5"><tr valign="middle"> <td width="100%" align="left" class="shortcuts"></td> <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td> <td><a accesskey="u" href="integration.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="integration.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="integration-uniscribe.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="integration-freetype"></a>FreeType integration</h2></div></div></div> <p> FreeType is the free-software font-rendering engine included in desktop Linux distributions, Android, ChromeOS, iOS, and multiple Unix operating systems, and used by cross-platform programs like Chrome, Java, and GhostScript. Used together, HarfBuzz can perform shaping on Unicode text segments, outputting the glyph IDs that FreeType should rasterize from the active font as well as the positions at which those glyphs should be drawn. </p> <p> HarfBuzz provides integration points with FreeType at the face-object and font-object level and for the font-functions virtual-method structure of a font object. To use the FreeType-integration API, include the <code class="filename">hb-ft.h</code> header. </p> <p> In a typical client program, you will create your <span class="type">hb_face_t</span> face object and <span class="type">hb_font_t</span> font object from a FreeType <span class="type">FT_Face</span>. HarfBuzz provides a suite of functions for doing this. </p> <p> In the most common case, you will want to use <code class="function">hb_ft_font_create_referenced()</code>, which creates both an <span class="type">hb_face_t</span> face object and <span class="type">hb_font_t</span> font object (linked to that face object), and provides lifecycle management. </p> <p> It is important to note, though, that while HarfBuzz makes a distinction between its face and font objects, FreeType's <span class="type">FT_Face</span> does not. After you create your <span class="type">FT_Face</span>, you must set its size parameter using <code class="function">FT_Set_Char_Size()</code>, because an <span class="type">hb_font_t</span> is defined as an instance of an <span class="type">hb_face_t</span> with size specified. </p> <pre class="programlisting"> #include <hb-ft.h> ... FT_New_Face(ft_library, font_path, index, &face); FT_Set_Char_Size(face, 0, 1000, 0, 0); hb_font_t *font = hb_ft_font_create(face); </pre> <p> <code class="function">hb_ft_font_create_referenced()</code> is the recommended function for creating an <span class="type">hb_face_t</span> face object. This function calls <code class="function">FT_Reference_Face()</code> before using the <span class="type">FT_Face</span> and calls <code class="function">FT_Done_Face()</code> when it is finished using the <span class="type">FT_Face</span>. Consequently, your client program does not need to worry about destroying the <span class="type">FT_Face</span> while HarfBuzz is still using it. </p> <p> Although <code class="function">hb_ft_font_create_referenced()</code> is the recommended function, there is another variant for client code where special circumstances make it necessary. The simpler version of the function is <code class="function">hb_ft_font_create()</code>, which takes an <span class="type">FT_Face</span> and an optional destroy callback as its arguments. Because <code class="function">hb_ft_font_create()</code> does not offer lifecycle management, however, your client code will be responsible for tracking references to the <span class="type">FT_Face</span> objects and destroying them when they are no longer needed. If you do not have a valid reason for doing this, use <code class="function">hb_ft_font_create_referenced()</code>. </p> <p> After you have created your font object from your <span class="type">FT_Face</span>, you can set or retrieve the <em class="structfield"><code>load_flags</code></em> of the <span class="type">FT_Face</span> through the <span class="type">hb_font_t</span> object. HarfBuzz provides <code class="function">hb_ft_font_set_load_flags()</code> and <code class="function">hb_ft_font_get_load_flags()</code> for this purpose. The ability to set the <em class="structfield"><code>load_flags</code></em> through the font object could be useful for enabling or disabling hinting, for example, or to activate vertical layout. </p> <p> HarfBuzz also provides a utility function called <code class="function">hb_ft_font_has_changed()</code> that you should call whenever you have altered the properties of your underlying <span class="type">FT_Face</span>, as well as a <code class="function">hb_ft_get_face()</code> that you can call on an <span class="type">hb_font_t</span> font object to fetch its underlying <span class="type">FT_Face</span>. </p> <p> With an <span class="type">hb_face_t</span> and <span class="type">hb_font_t</span> both linked to your <span class="type">FT_Face</span>, you will typically also want to use FreeType for the <em class="structfield"><code>font_funcs</code></em> vtable of your <span class="type">hb_font_t</span>. As a reminder, this font-functions structure is the set of methods that HarfBuzz will use to fetch important information from the font, such as the advances and extents of individual glyphs. </p> <p> All you need to do is call </p> <pre class="programlisting"> hb_ft_font_set_funcs(font); </pre> <p> and HarfBuzz will use FreeType for the font-functions in <code class="literal">font</code>. </p> <p> As we noted above, an <span class="type">hb_font_t</span> is derived from an <span class="type">hb_face_t</span> with size (and, perhaps, other parameters, such as variation-axis coordinates) specified. Consequently, you can reuse an <span class="type">hb_face_t</span> with several <span class="type">hb_font_t</span> objects, and HarfBuzz provides functions to simplify this. </p> <p> The <code class="function">hb_ft_face_create_referenced()</code> function creates just an <span class="type">hb_face_t</span> from a FreeType <span class="type">FT_Face</span> and, as with <code class="function">hb_ft_font_create_referenced()</code> above, provides lifecycle management for the <span class="type">FT_Face</span>. </p> <p> Similarly, there is an <code class="function">hb_ft_face_create()</code> function variant that does not provide the lifecycle-management feature. As with the font-object case, if you use this version of the function, it will be your client code's respsonsibility to track usage of the <span class="type">FT_Face</span> objects. </p> <p> A third variant of this function is <code class="function">hb_ft_face_create_cached()</code>, which is the same as <code class="function">hb_ft_face_create()</code> except that it also uses the <em class="structfield"><code>generic</code></em> field of the <span class="type">FT_Face</span> structure to save a pointer to the newly created <span class="type">hb_face_t</span>. Subsequently, function calls that pass the same <span class="type">FT_Face</span> will get the same <span class="type">hb_face_t</span> returned — and the <span class="type">hb_face_t</span> will be correctly reference counted. Still, as with <code class="function">hb_ft_face_create()</code>, your client code must track references to the <span class="type">FT_Face</span> itself, and destroy it when it is unneeded. </p> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>