cairo-scaled-font.xml

按照官方的说法：Cairo is a vector graphics library with cross-device output support. 翻译过来

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<refentry id="cairo-Scaled-Fonts">
<refmeta>
<refentrytitle id="top_of_page">Scaled Fonts</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>CAIRO Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>Scaled Fonts</refname>
<refpurpose>Caching metrics for a particular font size</refpurpose>
<!--[<xref linkend="desc" endterm="desc.title"/>]-->
</refnamediv>

<refsynopsisdiv id="synopsis">
<title id="synopsis.title">Synopsis</title>

<synopsis>



typedef     <link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link>;
<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link>* <link linkend="cairo-scaled-font-create">cairo_scaled_font_create</link>
                                            (<link linkend="cairo-font-face-t">cairo_font_face_t</link> *font_face,
                                             const <link linkend="cairo-matrix-t">cairo_matrix_t</link> *font_matrix,
                                             const <link linkend="cairo-matrix-t">cairo_matrix_t</link> *ctm,
                                             const <link linkend="cairo-font-options-t">cairo_font_options_t</link> *options);
<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link>* <link linkend="cairo-scaled-font-reference">cairo_scaled_font_reference</link>
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-destroy">cairo_scaled_font_destroy</link>       (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);
<link linkend="cairo-status-t">cairo_status_t</link> <link linkend="cairo-scaled-font-status">cairo_scaled_font_status</link>     (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);
            <link linkend="cairo-font-extents-t">cairo_font_extents_t</link>;
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-extents">cairo_scaled_font_extents</link>       (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             <link linkend="cairo-font-extents-t">cairo_font_extents_t</link> *extents);
            <link linkend="cairo-text-extents-t">cairo_text_extents_t</link>;
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-text-extents">cairo_scaled_font_text_extents</link>  (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             const <link linkend="char">char</link> *utf8,
                                             <link linkend="cairo-text-extents-t">cairo_text_extents_t</link> *extents);
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-glyph-extents">cairo_scaled_font_glyph_extents</link> (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             <link linkend="cairo-glyph-t">cairo_glyph_t</link> *glyphs,
                                             <link linkend="int">int</link> num_glyphs,
                                             <link linkend="cairo-text-extents-t">cairo_text_extents_t</link> *extents);
<link linkend="cairo-font-face-t">cairo_font_face_t</link>* <link linkend="cairo-scaled-font-get-font-face">cairo_scaled_font_get_font_face</link>
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-get-font-options">cairo_scaled_font_get_font_options</link>
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             <link linkend="cairo-font-options-t">cairo_font_options_t</link> *options);
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-get-font-matrix">cairo_scaled_font_get_font_matrix</link>
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             <link linkend="cairo-matrix-t">cairo_matrix_t</link> *font_matrix);
<link linkend="void">void</link>        <link linkend="cairo-scaled-font-get-ctm">cairo_scaled_font_get_ctm</link>       (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font,
                                             <link linkend="cairo-matrix-t">cairo_matrix_t</link> *ctm);
<link linkend="cairo-font-type-t">cairo_font_type_t</link> <link linkend="cairo-scaled-font-get-type">cairo_scaled_font_get_type</link>
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);
</synopsis>
</refsynopsisdiv>









<refsect1 id="desc">
<title id="desc.title">Description</title>
<para>

</para>
</refsect1>

<refsect1 id="details">
<title id="details.title">Details</title>
<refsect2>
<title><anchor id="cairo-scaled-font-t" role="typedef"/>cairo_scaled_font_t</title>
<indexterm><primary>cairo_scaled_font_t</primary></indexterm><programlisting>typedef struct _cairo_scaled_font cairo_scaled_font_t;
</programlisting>
<para>
A <link linkend="cairo-scaled-font-t"><type>cairo_scaled_font_t</type></link> is a font scaled to a particular size and device
resolution. A cairo_scaled_font_t is most useful for low-level font
usage where a library or application wants to cache a reference
to a scaled font to speed up the computation of metrics.</para>
<para>

</para></refsect2>
<refsect2>
<title><anchor id="cairo-scaled-font-create" role="function"/>cairo_scaled_font_create ()</title>
<indexterm><primary>cairo_scaled_font_create</primary></indexterm><programlisting><link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link>* cairo_scaled_font_create
                                            (<link linkend="cairo-font-face-t">cairo_font_face_t</link> *font_face,
                                             const <link linkend="cairo-matrix-t">cairo_matrix_t</link> *font_matrix,
                                             const <link linkend="cairo-matrix-t">cairo_matrix_t</link> *ctm,
                                             const <link linkend="cairo-font-options-t">cairo_font_options_t</link> *options);</programlisting>
</refsect2>
<refsect2>
<title><anchor id="cairo-scaled-font-reference" role="function"/>cairo_scaled_font_reference ()</title>
<indexterm><primary>cairo_scaled_font_reference</primary></indexterm><programlisting><link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link>* cairo_scaled_font_reference
                                            (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);</programlisting>
</refsect2>
<refsect2>
<title><anchor id="cairo-scaled-font-destroy" role="function"/>cairo_scaled_font_destroy ()</title>
<indexterm><primary>cairo_scaled_font_destroy</primary></indexterm><programlisting><link linkend="void">void</link>        cairo_scaled_font_destroy       (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);</programlisting>
</refsect2>
<refsect2>
<title><anchor id="cairo-scaled-font-status" role="function"/>cairo_scaled_font_status ()</title>
<indexterm><primary>cairo_scaled_font_status</primary></indexterm><programlisting><link linkend="cairo-status-t">cairo_status_t</link> cairo_scaled_font_status     (<link linkend="cairo-scaled-font-t">cairo_scaled_font_t</link> *scaled_font);</programlisting>
</refsect2>
<refsect2>
<title><anchor id="cairo-font-extents-t" role="struct"/>cairo_font_extents_t</title>
<indexterm><primary>cairo_font_extents_t</primary></indexterm><programlisting>typedef struct {
    double ascent;
    double descent;
    double height;
    double max_x_advance;
    double max_y_advance;
} cairo_font_extents_t;
</programlisting>
<para>
The <link linkend="cairo-text-extents-t"><type>cairo_text_extents_t</type></link> structure stores metric information for
a font. Values are given in the current user-space coordinate
system.
</para>
<para>
Because font metrics are in user-space coordinates, they are
mostly, but not entirely, independent of the current transformation
matrix. If you call <literal>cairo_scale(cr, 2.0, 2.0)</literal>,
text will be drawn twice as big, but the reported text extents will
not be doubled. They will change slightly due to hinting (so you
can't assume that metrics are independent of the transformation
matrix), but otherwise will remain unchanged.</para>
<para>

</para><variablelist role="struct">
<varlistentry>
<term><link linkend="double">double</link>&nbsp;<structfield>ascent</structfield>;</term>
<listitem><simpara> the distance that the font extends above the baseline.
         Note that this is not always exactly equal to the maximum
         of the extents of all the glyphs in the font, but rather
         is picked to express the font designer's intent as to
         how the font should align with elements above it.
</simpara></listitem>
</varlistentry>
<varlistentry>
<term><link linkend="double">double</link>&nbsp;<structfield>descent</structfield>;</term>
<listitem><simpara> the distance that the font extends below the baseline.
          This value is positive for typical fonts that include
          portions below the baseline. Note that this is not always
          exactly equal to the maximum of the extents of all the
          glyphs in the font, but rather is picked to express the