pangocairo.xml

GTK+-2.0源码之pango-1.15.6.tar.gz

<refentry id="pango-Cairo-Rendering">
<refmeta>
<refentrytitle id="top_of_page">Cairo Rendering</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>PANGO Library</refmiscinfo>
</refmeta>

<refnamediv>
<refname>Cairo Rendering</refname>
<refpurpose>Rendering with the Cairo backend</refpurpose>
<!--[<xref linkend="desc" endterm="desc.title"/>]-->
</refnamediv>

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



            <link linkend="PangoCairoFontMap-struct">PangoCairoFontMap</link>;
<link linkend="PangoFontMap">PangoFontMap</link>* <link linkend="pango-cairo-font-map-new">pango_cairo_font_map_new</link>      (void);
<link linkend="PangoFontMap">PangoFontMap</link>* <link linkend="pango-cairo-font-map-get-default">pango_cairo_font_map_get_default</link>
                                            (void);
<link linkend="void">void</link>        <link linkend="pango-cairo-font-map-set-resolution">pango_cairo_font_map_set_resolution</link>
                                            (<link linkend="PangoCairoFontMap">PangoCairoFontMap</link> *fontmap,
                                             <link linkend="double">double</link> dpi);
<link linkend="double">double</link>      <link linkend="pango-cairo-font-map-get-resolution">pango_cairo_font_map_get_resolution</link>
                                            (<link linkend="PangoCairoFontMap">PangoCairoFontMap</link> *fontmap);
<link linkend="PangoContext">PangoContext</link>* <link linkend="pango-cairo-font-map-create-context">pango_cairo_font_map_create_context</link>
                                            (<link linkend="PangoCairoFontMap">PangoCairoFontMap</link> *fontmap);
<link linkend="void">void</link>        <link linkend="pango-cairo-context-set-resolution">pango_cairo_context_set_resolution</link>
                                            (<link linkend="PangoContext">PangoContext</link> *context,
                                             <link linkend="double">double</link> dpi);
<link linkend="double">double</link>      <link linkend="pango-cairo-context-get-resolution">pango_cairo_context_get_resolution</link>
                                            (<link linkend="PangoContext">PangoContext</link> *context);
<link linkend="void">void</link>        <link linkend="pango-cairo-context-set-font-options">pango_cairo_context_set_font_options</link>
                                            (<link linkend="PangoContext">PangoContext</link> *context,
                                             const <link linkend="cairo-font-options-t">cairo_font_options_t</link> *options);
const <link linkend="cairo-font-options-t">cairo_font_options_t</link>* <link linkend="pango-cairo-context-get-font-options">pango_cairo_context_get_font_options</link>
                                            (<link linkend="PangoContext">PangoContext</link> *context);
<link linkend="void">void</link>        <link linkend="pango-cairo-update-context">pango_cairo_update_context</link>      (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoContext">PangoContext</link> *context);
<link linkend="PangoLayout">PangoLayout</link>* <link linkend="pango-cairo-create-layout">pango_cairo_create_layout</link>      (<link linkend="cairo-t">cairo_t</link> *cr);
<link linkend="void">void</link>        <link linkend="pango-cairo-update-layout">pango_cairo_update_layout</link>       (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoLayout">PangoLayout</link> *layout);
<link linkend="void">void</link>        <link linkend="pango-cairo-show-glyph-string">pango_cairo_show_glyph_string</link>   (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoFont">PangoFont</link> *font,
                                             <link linkend="PangoGlyphString">PangoGlyphString</link> *glyphs);
<link linkend="void">void</link>        <link linkend="pango-cairo-show-layout-line">pango_cairo_show_layout_line</link>    (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoLayoutLine">PangoLayoutLine</link> *line);
<link linkend="void">void</link>        <link linkend="pango-cairo-show-layout">pango_cairo_show_layout</link>         (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoLayout">PangoLayout</link> *layout);
<link linkend="void">void</link>        <link linkend="pango-cairo-show-error-underline">pango_cairo_show_error_underline</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="pango-cairo-glyph-string-path">pango_cairo_glyph_string_path</link>   (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoFont">PangoFont</link> *font,
                                             <link linkend="PangoGlyphString">PangoGlyphString</link> *glyphs);
<link linkend="void">void</link>        <link linkend="pango-cairo-layout-line-path">pango_cairo_layout_line_path</link>    (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoLayoutLine">PangoLayoutLine</link> *line);
<link linkend="void">void</link>        <link linkend="pango-cairo-layout-path">pango_cairo_layout_path</link>         (<link linkend="cairo-t">cairo_t</link> *cr,
                                             <link linkend="PangoLayout">PangoLayout</link> *layout);
<link linkend="void">void</link>        <link linkend="pango-cairo-error-underline-path">pango_cairo_error_underline_path</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);

</synopsis>
</refsynopsisdiv>

<refsect1 id="object_hierarchy">
<title id="object_hierarchy.title">Object Hierarchy</title>
<synopsis>

  <link linkend="GInterface">GInterface</link>
   +----PangoCairoFontMap
</synopsis>

</refsect1>

<refsect1 id="prerequisites">
<title id="prerequisites.title">Prerequisites</title>
<para>
PangoCairoFontMap requires
 <link linkend="PangoFontMap">PangoFontMap</link>.</para>

</refsect1>







<refsect1 id="desc">
<title id="desc.title">Description</title>
<para>
The <ulink url="http://cairographics.org">Cairo library</ulink> is a
vector graphics library with a powerful rendering model. It has such
features as anti-aliased primitives, alpha-compositing, and
gradients. Multiple backends for Cairo are available, to allow
rendering to images, to PDF files, and to the screen on X and on other
windowing systems. The functions in this section allow using Pango
to render to Cairo surfaces.
</para>
<para>
Using Pango with Cairo is straightforward. A <link linkend="PangoContext"><type>PangoContext</type></link> created
with <link linkend="pango-cairo-font-map-create-context"><function>pango_cairo_font_map_create_context()</function></link> can be used on any
Cairo context (cairo_t), but needs to be updated to match the
current transformation matrix and target surface of the Cairo context
using <link linkend="pango-cairo-update-context"><function>pango_cairo_update_context()</function></link>. The convenience functions
<link linkend="pango-cairo-create-layout"><function>pango_cairo_create_layout()</function></link> and <link linkend="pango-cairo-update-layout"><function>pango_cairo_update_layout()</function></link> handle
the common case where the program doesn't need to manipulate the
properties of the <link linkend="PangoContext"><type>PangoContext</type></link>.
</para>
<para>
When you get the metrics of a layout or of a piece of a layout using
functions such as <link linkend="pango-layout-get-extents"><function>pango_layout_get_extents()</function></link>, the reported metrics
are in user-space coordinates. If a piece of text is 10 units long,
and you call cairo_scale (cr, 2.0), it still is more-or-less 10
units long. However, the results will be affected by hinting
(that is, the process of adjusting the text to look good on the
pixel grid), so you shouldn't assume they are completely independent
of the current transformation matrix. Note that the basic metrics
functions in Pango report results in integer Pango units. To get
to the floating point units used in Cairo divide by <link linkend="PANGO-SCALE:CAPS"><literal>PANGO_SCALE</literal></link>.
</para>
<example id="rotated-example">
<title>Using Pango with Cairo</title>
<programlisting>
#<!-- -->include &lt;math.h>
#<!-- -->include &lt;pango/pangocairo.h>

static void
draw_text (cairo_t *cr)
{
#<!-- -->define RADIUS 150
#<!-- -->define N_WORDS 10
#<!-- -->define FONT "Sans Bold 27"

  PangoLayout *layout;
  PangoFontDescription *desc;
  int i;

  /* Center coordinates on the middle of the region we are drawing
   */
  cairo_translate (cr, RADIUS, RADIUS);

  /* Create a PangoLayout, set the font and text */
  layout = pango_cairo_create_layout (cr);
  
  pango_layout_set_text (layout, "Text", -1);
  desc = pango_font_description_from_string (FONT);
  pango_layout_set_font_description (layout, desc);
  pango_font_description_free (desc);

  /* Draw the layout N_WORDS times in a circle */
  for (i = 0; i &lt; N_WORDS; i++)
    {
      int width, height;
      double angle = (360. * i) / N_WORDS;
      double red;

      cairo_save (cr);

      /* Gradient from red at angle == 60 to blue at angle == 240 */
      red   = (1 + cos ((angle - 60) * G_PI / 180.)) / 2;
      cairo_set_source_rgb (cr, red, 0, 1.0 - red);

      cairo_rotate (cr, angle * G_PI / 180.);
    
      /* Inform Pango to re-layout the text with the new transformation */
      pango_cairo_update_layout (cr, layout);
    
      pango_layout_get_size (layout, &amp;width, &amp;height);
      cairo_move_to (cr, - ((double)width / PANGO_SCALE) / 2, - RADIUS);
      pango_cairo_show_layout (cr, layout);

      cairo_restore (cr);
    }

  /* free the layout object */
  g_object_unref (layout);
}

int main (int argc, char **argv)
{
  cairo_t *cr;
  char *filename;
  cairo_status_t status;
  cairo_surface_t *surface;

  if (argc != 2)
    {
      g_printerr ("Usage: cairosimple OUTPUT_FILENAME\n");
      return 1;
    }

  filename = argv[1];

  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
					2 * RADIUS, 2 * RADIUS);
  cr = cairo_create (surface);
				  

  cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
  cairo_paint (cr);
  draw_text (cr);
  cairo_destroy (cr);
  
  status = cairo_surface_write_to_png (surface, filename);
  cairo_surface_destroy (surface);

  if (status != CAIRO_STATUS_SUCCESS)
    {
      g_printerr ("Could not save png to '<link linkend="s"><literal>s</literal></link>'\n", filename);
      return 1;
    }

  return 0;
}
</programlisting>
</example>
<figure>