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[manual] Fix font functions section 

Fixes https://github.com/harfbuzz/harfbuzz/issues/2731
This commit is contained in:
Khaled Hosny 2021-01-01 01:31:19 +02:00
parent 3583fce86d
commit 319e5b3200
1 changed files with 20 additions and 7 deletions
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27
docs/usermanual-fonts-and-faces.xml
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@ -260,18 +260,18 @@
</listitem> </listitem>
</itemizedlist> </itemizedlist>
<para> <para>
You can fetch the font-functions configuration for a font object You can create new font-functions by calling
by calling <function>hb_font_get_font_funcs()</function>: <function>hb_font_funcs_create()</function>:
</para> </para>
<programlisting language="C"> <programlisting language="C">
hb_font_funcs_t *ffunctions; hb_font_funcs_t *ffunctions = hb_font_funcs_create ();
ffunctions = hb_font_get_font_funcs (font); hb_font_set_funcs (font, ffunctions, font_data, destroy);
</programlisting> </programlisting>
<para> <para>
The individual methods can each be replaced with their own setter The individual methods can each be set with their own setter
function, such as function, such as
<function>hb_font_funcs_set_nominal_glyph_func(*ffunctions, <function>hb_font_funcs_set_nominal_glyph_func(ffunctions,
func, *user_data, destroy)</function>. func, user_data, destroy)</function>.
</para> </para>
<para> <para>
Font-functions structures can be reused for multiple font Font-functions structures can be reused for multiple font
@ -291,6 +291,19 @@
programs from changing the configuration and introducing programs from changing the configuration and introducing
inconsistencies and errors downstream. inconsistencies and errors downstream.
</para> </para>
<para>
To override only some functions while using the default implementation
for the others, you will need to create a sub-font. By default, the
sub-font uses the font functions of its parent except for the functions
that were explicitly set. The following code will override only the
<function>hb_font_get_nominal_glyph_func_t</function> for the sub-font:
</para>
<programlisting language="C">
hb_font_t *subfont = hb_font_create_sub_font (font)
hb_font_funcs_t *ffunctions = hb_font_funcs_create ();
hb_font_funcs_set_nominal_glyph_func(ffunctions, func, user_data, destroy);
hb_font_set_funcs (subfont, ffunctions, font_data, destroy);
</programlisting>
</section> </section>
<section id="fonts-and-faces-native-opentype"> <section id="fonts-and-faces-native-opentype">