1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
4 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
5 <title>Setting buffer properties: HarfBuzz Manual</title>
6 <meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
7 <link rel="home" href="index.html" title="HarfBuzz Manual">
8 <link rel="up" href="buffers-language-script-and-direction.html" title="Buffers, language, script and direction">
9 <link rel="prev" href="adding-text-to-the-buffer.html" title="Adding text to the buffer">
10 <link rel="next" href="customizing-unicode-functions.html" title="Customizing Unicode functions">
11 <meta name="generator" content="GTK-Doc V1.32.1 (XML mode)">
12 <link rel="stylesheet" href="style.css" type="text/css">
14 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
15 <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="5"><tr valign="middle">
16 <td width="100%" align="left" class="shortcuts"></td>
17 <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td>
18 <td><a accesskey="u" href="buffers-language-script-and-direction.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td>
19 <td><a accesskey="p" href="adding-text-to-the-buffer.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td>
20 <td><a accesskey="n" href="customizing-unicode-functions.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td>
23 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
24 <a name="setting-buffer-properties"></a>Setting buffer properties</h2></div></div></div>
26 Buffers containing input characters still need several
27 properties set before HarfBuzz can shape their text correctly.
30 Initially, all buffers are set to the
31 <code class="literal">HB_BUFFER_CONTENT_TYPE_INVALID</code> content
32 type. After adding text, the buffer should be set to
33 <code class="literal">HB_BUFFER_CONTENT_TYPE_UNICODE</code> instead, which
34 indicates that it contains un-shaped input
35 characters. After shaping, the buffer will have the
36 <code class="literal">HB_BUFFER_CONTENT_TYPE_GLYPHS</code> content type.
39 <code class="function">hb_buffer_add_utf8()</code> and the
40 other UTF functions set the content type of their buffer
41 automatically. But if you are reusing a buffer you may want to
43 <code class="function">hb_buffer_get_content_type(buffer)</code>. If
44 necessary you can set the content type with
46 <pre class="programlisting">
47 hb_buffer_set_content_type(buf, HB_BUFFER_CONTENT_TYPE_UNICODE);
50 to prepare for shaping.
53 Buffers also need to carry information about the script,
54 language, and text direction of their contents. You can set
55 these properties individually:
57 <pre class="programlisting">
58 hb_buffer_set_direction(buf, HB_DIRECTION_LTR);
59 hb_buffer_set_script(buf, HB_SCRIPT_LATIN);
60 hb_buffer_set_language(buf, hb_language_from_string("en", -1));
63 However, since these properties are often repeated for
64 multiple text runs, you can also save them in a
65 <code class="literal">hb_segment_properties_t</code> for reuse:
67 <pre class="programlisting">
68 hb_segment_properties_t *savedprops;
69 hb_buffer_get_segment_properties (buf, savedprops);
71 hb_buffer_set_segment_properties (buf2, savedprops);
74 HarfBuzz also provides getter functions to retrieve a buffer's
75 direction, script, and language properties individually.
78 HarfBuzz recognizes four text directions in
79 <span class="type">hb_direction_t</span>: left-to-right
80 (<code class="literal">HB_DIRECTION_LTR</code>), right-to-left (<code class="literal">HB_DIRECTION_RTL</code>),
81 top-to-bottom (<code class="literal">HB_DIRECTION_TTB</code>), and
82 bottom-to-top (<code class="literal">HB_DIRECTION_BTT</code>). For the
83 script property, HarfBuzz uses identifiers based on the
84 <a class="ulink" href="https://unicode.org/iso15924/" target="_top">ISO 15924
85 standard</a>. For languages, HarfBuzz uses tags based on the
86 <a class="ulink" href="https://tools.ietf.org/html/bcp47" target="_top">IETF BCP 47</a> standard.
89 Helper functions are provided to convert character strings into
90 the necessary script and language tag types.
93 Two additional buffer properties to be aware of are the
94 "invisible glyph" and the replacement code point. The
95 replacement code point is inserted into buffer output in place of
96 any invalid code points encountered in the input. By default, it
97 is the Unicode <code class="literal">REPLACEMENT CHARACTER</code> code
98 point, <code class="literal">U+FFFD</code> "�". You can change this with
100 <pre class="programlisting">
101 hb_buffer_set_replacement_codepoint(buf, replacement);
104 passing in the replacement Unicode code point as the
105 <em class="parameter"><code>replacement</code></em> parameter.
108 The invisible glyph is used to replace all output glyphs that
109 are invisible. By default, the standard space character
110 <code class="literal">U+0020</code> is used; you can replace this (for
111 example, when using a font that provides script-specific
114 <pre class="programlisting">
115 hb_buffer_set_invisible_glyph(buf, replacement_glyph);
118 Do note that in the <em class="parameter"><code>replacement_glyph</code></em>
119 parameter, you must provide the glyph ID of the replacement you
120 wish to use, not the Unicode code point.
123 HarfBuzz supports a few additional flags you might want to set
124 on your buffer under certain circumstances. The
125 <code class="literal">HB_BUFFER_FLAG_BOT</code> and
126 <code class="literal">HB_BUFFER_FLAG_EOT</code> flags tell HarfBuzz
127 that the buffer represents the beginning or end (respectively)
128 of a text element (such as a paragraph or other block). Knowing
129 this allows HarfBuzz to apply certain contextual font features
130 when shaping, such as initial or final variants in connected
134 <code class="literal">HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES</code>
135 tells HarfBuzz not to hide glyphs with the
136 <code class="literal">Default_Ignorable</code> property in Unicode. This
137 property designates control characters and other non-printing
138 code points, such as joiners and variation selectors. Normally
139 HarfBuzz replaces them in the output buffer with zero-width
140 space glyphs (using the "invisible glyph" property discussed
141 above); setting this flag causes them to be printed, which can
142 be helpful for troubleshooting.
145 Conversely, setting the
146 <code class="literal">HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES</code> flag
147 tells HarfBuzz to remove <code class="literal">Default_Ignorable</code>
148 glyphs from the output buffer entirely. Finally, setting the
149 <code class="literal">HB_BUFFER_FLAG_DO_NOT_INSERT_DOTTED_CIRCLE</code>
150 flag tells HarfBuzz not to insert the dotted-circle glyph
151 (<code class="literal">U+25CC</code>, "◌"), which is normally
152 inserted into buffer output when broken character sequences are
153 encountered (such as combining marks that are not attached to a
158 <hr>Generated by GTK-Doc V1.32.1</div>