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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>Fonts, faces, and output: 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="pt01.html" title="Part I. User's manual"> <link rel="prev" href="customizing-unicode-functions.html" title="Customizing Unicode functions"> <link rel="next" href="fonts-and-faces-custom-functions.html" title="Customizing font functions"> <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="pt01.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="customizing-unicode-functions.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="fonts-and-faces-custom-functions.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="chapter"> <div class="titlepage"><div><div><h2 class="title"> <a name="fonts-and-faces"></a>Fonts, faces, and output</h2></div></div></div> <div class="toc"><dl class="toc"> <dt><span class="section"><a href="fonts-and-faces.html#fonts-and-faces-objects">Font and face objects</a></span></dt> <dt><span class="section"><a href="fonts-and-faces-custom-functions.html">Customizing font functions</a></span></dt> <dt><span class="section"><a href="fonts-and-faces-native-opentype.html">Font objects and HarfBuzz's native OpenType implementation</a></span></dt> <dt><span class="section"><a href="fonts-and-faces-variable.html">Working with OpenType Variable Fonts</a></span></dt> </dl></div> <p> In the previous chapter, we saw how to set up a buffer and fill it with text as Unicode code points. In order to shape this buffer text with HarfBuzz, you will need also need a font object. </p> <p> HarfBuzz provides abstractions to help you cache and reuse the heavier parts of working with binary fonts, so we will look at how to do that. We will also look at how to work with the FreeType font-rendering library and at how you can customize HarfBuzz to work with other libraries. </p> <p> Finally, we will look at how to work with OpenType variable fonts, the latest update to the OpenType font format, and at some other recent additions to OpenType. </p> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="fonts-and-faces-objects"></a>Font and face objects</h2></div></div></div> <p> The outcome of shaping a run of text depends on the contents of a specific font file (such as the substitutions and positioning moves in the 'GSUB' and 'GPOS' tables), so HarfBuzz makes accessing those internals fast. </p> <p> An <span class="type">hb_face_t</span> represents a <span class="emphasis"><em>face</em></span> in HarfBuzz. This data type is a wrapper around an <span class="type">hb_blob_t</span> blob that holds the contents of a binary font file. Since HarfBuzz supports TrueType Collections and OpenType Collections (each of which can include multiple typefaces), a HarfBuzz face also requires an index number specifying which typeface in the file you want to use. Most of the font files you will encounter in the wild include just a single face, however, so most of the time you would pass in <code class="literal">0</code> as the index when you create a face: </p> <pre class="programlisting"> hb_blob_t* blob = hb_blob_create_from_file(file); ... hb_face_t* face = hb_face_create(blob, 0); </pre> <p> On its own, a face object is not quite ready to use for shaping. The typeface must be set to a specific point size in order for some details (such as hinting) to work. In addition, if the font file in question is an OpenType Variable Font, then you may need to specify one or variation-axis settings (or a named instance) in order to get the output you need. </p> <p> In HarfBuzz, you do this by creating a <span class="emphasis"><em>font</em></span> object from your face. </p> <p> Font objects also have the advantage of being considerably lighter-weight than face objects (remember that a face contains the contents of a binary font file mapped into memory). As a result, you can cache and reuse a font object, but you could also create a new one for each additional size you needed. Creating new fonts incurs some additional overhead, of course, but whether or not it is excessive is your call in the end. In contrast, face objects are substantially larger, and you really should cache them and reuse them whenever possible. </p> <p> You can create a font object from a face object: </p> <pre class="programlisting"> hb_font_t* hb_font = hb_font_create(hb_face); </pre> <p> After creating a font, there are a few properties you should set. Many fonts enable and disable hints based on the size it is used at, so setting this is important for font objects. <code class="function">hb_font_set_ppem(font, x_ppem, y_ppem)</code> sets the pixels-per-EM value of the font. You can also set the point size of the font with <code class="function">hb_font_set_ptem(font, ptem)</code>. HarfBuzz uses the industry standard 72 points per inch. </p> <p> HarfBuzz lets you specify the degree subpixel precision you want through a scaling factor. You can set horizontal and vertical scaling factors on the font by calling <code class="function">hb_font_set_scale(font, x_scale, y_scale)</code>. </p> <p> There may be times when you are handed a font object and need to access the face object that it comes from. For that, you can call </p> <pre class="programlisting"> hb_face = hb_font_get_face(hb_font); </pre> <p> You can also create a font object from an existing font object using the <code class="function">hb_font_create_sub_font()</code> function. This creates a child font object that is initiated with the same attributes as its parent; it can be used to quickly set up a new font for the purpose of overriding a specific font-functions method. </p> <p> All face objects and font objects are lifecycle-managed by HarfBuzz. After creating a face, you increase its reference count with <code class="function">hb_face_reference(face)</code> and decrease it with <code class="function">hb_face_destroy(face)</code>. Likewise, you increase the reference count on a font with <code class="function">hb_font_reference(font)</code> and decrease it with <code class="function">hb_font_destroy(font)</code>. </p> <p> You can also attach user data to face objects and font objects. </p> </div> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>