Pango Interaction
Using Pango in GDK
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.
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 PANGO_SCALE or the PANGO_PIXELS() macro.)
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().
Draw transformed text with Pango and cairo
#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 < 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, &width, &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);
Output of <xref linkend="rotated-example"/>
@layout:
@x_origin:
@y_origin:
@index_ranges:
@n_ranges:
@Returns:
@line:
@x_origin:
@y_origin:
@index_ranges:
@n_ranges:
@Returns:
@void:
@Returns:
@screen:
@Returns: