cairo-paths.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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                "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<refentry id="cairo-Paths">
<refmeta>
<refentrytitle id="top_of_page">Paths</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>CAIRO Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>Paths</refname>
<refpurpose>Creating paths and manipulating path data</refpurpose>
<!--[<xref linkend="desc" endterm="desc.title"/>]-->
</refnamediv>

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

<synopsis>



            <link linkend="cairo-path-t">cairo_path_t</link>;
union       <link linkend="cairo-path-data-t">cairo_path_data_t</link>;
enum        <link linkend="cairo-path-data-type-t">cairo_path_data_type_t</link>;
<link linkend="cairo-path-t">cairo_path_t</link>* <link linkend="cairo-copy-path">cairo_copy_path</link>               (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="cairo-path-t">cairo_path_t</link>* <link linkend="cairo-copy-path-flat">cairo_copy_path_flat</link>          (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="void">void</link>        <link linkend="cairo-path-destroy">cairo_path_destroy</link>              (<link linkend="cairo-path-t">cairo_path_t</link> *path);
<link linkend="void">void</link>        <link linkend="cairo-append-path">cairo_append_path</link>               (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="cairo-path-t">cairo_path_t</link> *path);
<link linkend="void">void</link>        <link linkend="cairo-get-current-point">cairo_get_current_point</link>         (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> *x,
                                             <link linkend="double">double</link> *y);
<link linkend="void">void</link>        <link linkend="cairo-new-path">cairo_new_path</link>                  (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="void">void</link>        <link linkend="cairo-new-sub-path">cairo_new_sub_path</link>              (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="void">void</link>        <link linkend="cairo-close-path">cairo_close_path</link>                (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="void">void</link>        <link linkend="cairo-arc">cairo_arc</link>                       (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> xc,
                                             <link linkend="double">double</link> yc,
                                             <link linkend="double">double</link> radius,
                                             <link linkend="double">double</link> angle1,
                                             <link linkend="double">double</link> angle2);
<link linkend="void">void</link>        <link linkend="cairo-arc-negative">cairo_arc_negative</link>              (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> xc,
                                             <link linkend="double">double</link> yc,
                                             <link linkend="double">double</link> radius,
                                             <link linkend="double">double</link> angle1,
                                             <link linkend="double">double</link> angle2);
<link linkend="void">void</link>        <link linkend="cairo-curve-to">cairo_curve_to</link>                  (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> x1,
                                             <link linkend="double">double</link> y1,
                                             <link linkend="double">double</link> x2,
                                             <link linkend="double">double</link> y2,
                                             <link linkend="double">double</link> x3,
                                             <link linkend="double">double</link> y3);
<link linkend="void">void</link>        <link linkend="cairo-line-to">cairo_line_to</link>                   (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> x,
                                             <link linkend="double">double</link> y);
<link linkend="void">void</link>        <link linkend="cairo-move-to">cairo_move_to</link>                   (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> x,
                                             <link linkend="double">double</link> y);
<link linkend="void">void</link>        <link linkend="cairo-rectangle">cairo_rectangle</link>                 (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> x,
                                             <link linkend="double">double</link> y,
                                             <link linkend="double">double</link> width,
                                             <link linkend="double">double</link> height);
<link linkend="void">void</link>        <link linkend="cairo-glyph-path">cairo_glyph_path</link>                (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="cairo-glyph-t">cairo_glyph_t</link> *glyphs,
                                             <link linkend="int">int</link> num_glyphs);
<link linkend="void">void</link>        <link linkend="cairo-text-path">cairo_text_path</link>                 (<link linkend="cairo-t">cairo_t</link> *cr,
                                             const <link linkend="char">char</link> *utf8);
<link linkend="void">void</link>        <link linkend="cairo-rel-curve-to">cairo_rel_curve_to</link>              (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> dx1,
                                             <link linkend="double">double</link> dy1,
                                             <link linkend="double">double</link> dx2,
                                             <link linkend="double">double</link> dy2,
                                             <link linkend="double">double</link> dx3,
                                             <link linkend="double">double</link> dy3);
<link linkend="void">void</link>        <link linkend="cairo-rel-line-to">cairo_rel_line_to</link>               (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> dx,
                                             <link linkend="double">double</link> dy);
<link linkend="void">void</link>        <link linkend="cairo-rel-move-to">cairo_rel_move_to</link>               (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="double">double</link> dx,
                                             <link linkend="double">double</link> dy);
</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-path-t" role="struct"/>cairo_path_t</title>
<indexterm><primary>cairo_path_t</primary></indexterm><programlisting>typedef struct {
    cairo_status_t status;
    cairo_path_data_t *data;
    int num_data;
} cairo_path_t;
</programlisting>
<para>
A data structure for holding a path. This data structure serves as
the return value for <link linkend="cairo-copy-path-data"><function>cairo_copy_path_data()</function></link> and
<link linkend="cairo-copy-path-data-flat"><function>cairo_copy_path_data_flat()</function></link> as well the input value for
<link linkend="cairo-append-path"><function>cairo_append_path()</function></link>.
</para>
<para>
See <link linkend="cairo-path-data-t"><type>cairo_path_data_t</type></link> for hints on how to iterate over the
actual data within the path.
</para>
<para>
The num_data member gives the number of elements in the data
array. This number is larger than the number of independent path
portions (defined in <link linkend="cairo-path-data-type-t"><type>cairo_path_data_type_t</type></link>), since the data
includes both headers and coordinates for each portion.</para>
<para>

</para><variablelist role="struct">
<varlistentry>
<term><link linkend="cairo-status-t">cairo_status_t</link>&nbsp;<structfield>status</structfield>;</term>
<listitem><simpara> the current error status
</simpara></listitem>
</varlistentry>
<varlistentry>
<term><link linkend="cairo-path-data-t">cairo_path_data_t</link>&nbsp;*<structfield>data</structfield>;</term>
<listitem><simpara> the elements in the path
</simpara></listitem>
</varlistentry>
<varlistentry>
<term><link linkend="int">int</link>&nbsp;<structfield>num_data</structfield>;</term>
<listitem><simpara> the number of elements in the data array
</simpara></listitem>
</varlistentry>
</variablelist></refsect2>
<refsect2>
<title><anchor id="cairo-path-data-t" role="union"/>union cairo_path_data_t</title>
<indexterm><primary>cairo_path_data_t</primary></indexterm><programlisting>union cairo_path_data_t {
    struct {
	cairo_path_data_type_t type;
	int length;
    } header;
    struct {
	double x, y;
    } point;
};
</programlisting>
<para>
<link linkend="cairo-path-data-t"><type>cairo_path_data_t</type></link> is used to represent the path data inside a
<link linkend="cairo-path-t"><type>cairo_path_t</type></link>.
</para>
<para>
The data structure is designed to try to balance the demands of
efficiency and ease-of-use. A path is represented as an array of
<link linkend="cairo-path-data-t"><type>cairo_path_data_t</type></link>, which is a union of headers and points.
</para>
<para>
Each portion of the path is represented by one or more elements in
the array, (one header followed by 0 or more points). The length
value of the header is the number of array elements for the current
portion including the header, (ie. length == 1 + # of points), and
where the number of points for each element type must be as
follows:
</para>
<para>
<programlisting>
    <link linkend="CAIRO-PATH-MOVE-TO:CAPS"><literal>CAIRO_PATH_MOVE_TO</literal></link>:     1 point
    <link linkend="CAIRO-PATH-LINE-TO:CAPS"><literal>CAIRO_PATH_LINE_TO</literal></link>:     1 point