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Pango Interaction

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Using Pango in GDK

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<para>
Pango is the text layout system used by GDK and GTK+. The functions
and types in this section are used to obtain clip regions for
#PangoLayouts, and to get #PangoContexts that can be used with
GDK.
</para>
<para>
Creating a #PangoLayout object is the first step in rendering text,
and requires getting a handle to a #PangoContext. For GTK+ programs,
you'll usually want to use gtk_widget_get_pango_context(), or
gtk_widget_create_pango_layout(), rather than using the lowlevel
gdk_pango_context_get_for_screen(). Once you have a #PangoLayout, you
can set the text and attributes of it with Pango functions like
pango_layout_set_text() and get its size with pango_layout_get_size().
(Note that Pango uses a fixed point system internally, so converting
between Pango units and pixels using <link
linkend="PANGO-SCALE-CAPS">PANGO_SCALE</link> or the PANGO_PIXELS() macro.)
</para>
<para>
Rendering a Pango layout is done most simply with pango_cairo_show_layout();
you can also draw pieces of the layout with pango_cairo_show_layout_line().
</para>
<example id="rotated-example">
<title>Draw transformed text with Pango and cairo</title>
<!-- Note that this example is basically the same as
     demos/gtk-demo/rotated_text.c -->
<programlisting>
#define RADIUS 100
#define N_WORDS 10
#define FONT "Sans Bold 18"

PangoContext *context;
PangoLayout *layout;
PangoFontDescription *desc;

double radius;
int width, height;
int i;

/* Set up a transformation matrix so that the user space coordinates for
 * where we are drawing are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
 * We first center, then change the scale */

width = gdk_window_get_width (window);
height = gdk_window_get_height (window);
radius = MIN (width, height) / 2.;

cairo_translate (cr,
                 radius + (width - 2 * radius) / 2,
                 radius + (height - 2 * radius) / 2);
                 cairo_scale (cr, radius / RADIUS, radius / RADIUS);

/* Create a PangoLayout, set the font and text */
context = gdk_pango_context_get_for_screen (screen);
layout = pango_layout_new (context);
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++)
  {
    double red, green, blue;
    double angle = 2 * G_PI * i / n_words;

    cairo_save (cr);

    /* Gradient from red at angle == 60 to blue at angle == 300 */
    red = (1 + cos (angle - 60)) / 2;
    green = 0;
    blue = 1 - red;

    cairo_set_source_rgb (cr, red, green, blue);
    cairo_rotate (cr, angle);

    /* Inform Pango to re-layout the text with the new transformation matrix */
    pango_cairo_update_layout (cr, layout);

    pango_layout_get_size (layout, &amp;width, &amp;height);

    cairo_move_to (cr, - width / 2 / PANGO_SCALE, - DEFAULT_TEXT_RADIUS);
    pango_cairo_show_layout (cr, layout);

    cairo_restore (cr);
  }

g_object_unref (layout);
g_object_unref (context);
</programlisting>
</example>
<figure>
  <title>Output of <xref linkend="rotated-example"/></title>
  <graphic fileref="rotated-text.png" format="PNG"/>
</figure>

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<para>

</para>

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<!-- ##### FUNCTION gdk_pango_layout_get_clip_region ##### -->
<para>

</para>

@layout: 
@x_origin: 
@y_origin: 
@index_ranges: 
@n_ranges: 
@Returns: 


<!-- ##### FUNCTION gdk_pango_layout_line_get_clip_region ##### -->
<para>

</para>

@line: 
@x_origin: 
@y_origin: 
@index_ranges: 
@n_ranges: 
@Returns: 


<!-- ##### FUNCTION gdk_pango_context_get ##### -->
<para>

</para>

@void: 
@Returns: 


<!-- ##### FUNCTION gdk_pango_context_get_for_screen ##### -->
<para>

</para>

@screen: 
@Returns: 


