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24 <a name="fonts-and-faces-native-opentype"></a>Font objects and HarfBuzz's native OpenType implementation</h2></div></div></div>
26 By default, whenever HarfBuzz creates a font object, it will
27 configure the font to use a built-in set of font functions that
28 supports contemporary OpenType font internals. If you want to
29 work with OpenType or TrueType fonts, you should be able to use
30 these functions without difficulty.
33 Many of the methods in the font-functions structure deal with
34 the fundamental properties of glyphs that are required for
35 shaping text: extents (the maximums and minimums on each axis),
36 origins (the <code class="literal">(0,0)</code> coordinate point which
37 glyphs are drawn in reference to), and advances (the amount that
38 the cursor needs to be moved after drawing each glyph, including
39 any empty space for the glyph's side bearings).
42 As you can see in the list of functions, there are separate "horizontal"
43 and "vertical" variants depending on whether the text is set in
44 the horizontal or vertical direction. For some scripts, fonts
45 that are designed to support text set horizontally or vertically (for
46 example, in Japanese) may include metrics for both text
47 directions. When fonts don't include this information, HarfBuzz
48 does its best to transform what the font provides.
51 In addition to the direction-specific functions, HarfBuzz
52 provides some higher-level functions for fetching information
53 like extents and advances for a glyph. If you call
55 <pre class="programlisting">
56 hb_font_get_glyph_advance_for_direction(font, direction, extents);
59 then you can provide any <span class="type">hb_direction_t</span> as the
60 <em class="parameter"><code>direction</code></em> parameter, and HarfBuzz will
61 use the correct function variant for the text direction. There
62 are similar higher-level versions of the functions for fetching
63 extents, origin coordinates, and contour-point
64 coordinates. There are also addition and subtraction functions
65 for moving points with respect to the origin.
68 There are also methods for fetching the glyph ID that
69 corresponds to a Unicode code point (possibly when followed by a
70 variation-selector code point), fetching the glyph name from the
71 font, and fetching the glyph ID that corresponds to a glyph name
75 HarfBuzz also provides functions for converting between glyph
77 variables. <code class="function">hb_font_glyph_to_string(font, glyph, s,
78 size)</code> retrieves the name for the glyph ID
79 <em class="parameter"><code>glyph</code></em> from the font object. It generates a
80 generic name of the form <code class="literal">gidDDD</code> (where DDD is
81 the glyph index) if there is no name for the glyph in the
82 font. The <code class="function">hb_font_glyph_from_string(font, s, len,
83 glyph)</code> takes an input string <em class="parameter"><code>s</code></em>
84 and looks for a glyph with that name in the font, returning its
85 glyph ID in the <em class="parameter"><code>glyph</code></em>
86 output parameter. It automatically parses
87 <code class="literal">gidDDD</code> and <code class="literal">uniUUUU</code> strings.
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