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 render Pango objects to GDK.
drawables, and also extend the set of Pango attributes to include
stippling and embossing.
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 gdk_draw_layout();
you can also draw pieces of the layout with gdk_draw_layout() or
gdk_draw_glyphs(). #GdkPangoRenderer is a subclass of #PangoRenderer
that is used internally to implement these functions. Using it
directly or subclassing it can be useful in some cases. See the
#GdkPangoRenderer documentation for details.
Using #GdkPangoRenderer to draw transformed text
#define RADIUS 100
#define N_WORDS 10
#define FONT "Sans Bold 18"
GdkScreen *screen = gdk_drawable_get_screen (drawable);
PangoRenderer *renderer;
GdkGC *gc;
PangoMatrix matrix = PANGO_MATRIX_INIT;
PangoContext *context;
PangoLayout *layout;
PangoFontDescription *desc;
double device_radius;
int width, height;
int i;
/* Get the default renderer for the screen, and set it up for drawing */
renderer = gdk_pango_renderer_get_default (screen);
gdk_pango_renderer_set_drawable (GDK_PANGO_RENDERER (renderer), drawable);
gc = gdk_gc_new (drawable);
gdk_pango_renderer_set_gc (GDK_PANGO_RENDERER (renderer), gc);
/* 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 */
gdk_drawable_get_size (drawable, &width, &height);
device_radius = MIN (width, height) / 2.;
pango_matrix_translate (&matrix,
device_radius + (width - 2 * device_radius) / 2,
device_radius + (height - 2 * device_radius) / 2);
pango_matrix_scale (&matrix, device_radius / RADIUS, device_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++)
{
GdkColor color;
PangoMatrix rotated_matrix = matrix;
int width, height;
double angle = (360. * i) / N_WORDS;
/* Gradient from red at angle == 60 to blue at angle == 300 */
color.red = 65535 * (1 + cos ((angle - 60) * M_PI / 180.)) / 2;
color.green = 0;
color.blue = 65535 - color.red;
gdk_pango_renderer_set_override_color (GDK_PANGO_RENDERER (renderer),
PANGO_RENDER_PART_FOREGROUND, &color);
pango_matrix_rotate (&rotated_matrix, angle);
pango_context_set_matrix (context, &rotated_matrix);
/* Inform Pango to re-layout the text with the new transformation matrix */
pango_layout_context_changed (layout);
pango_layout_get_size (layout, &width, &height);
pango_renderer_draw_layout (renderer, layout,
- width / 2, - RADIUS * PANGO_SCALE);
}
/* Clean up default renderer, since it is shared */
gdk_pango_renderer_set_override_color (GDK_PANGO_RENDERER (renderer),
PANGO_RENDER_PART_FOREGROUND, NULL);
gdk_pango_renderer_set_drawable (GDK_PANGO_RENDERER (renderer), NULL);
gdk_pango_renderer_set_gc (GDK_PANGO_RENDERER (renderer), NULL);
/* free the objects we created */
g_object_unref (layout);
g_object_unref (context);
g_object_unref (gc);
Output of <xref linkend="rotated-example"/>
@screen:
@Returns:
@screen:
@Returns:
@gdk_renderer:
@drawable:
@gdk_renderer:
@gc:
@gdk_renderer:
@part:
@stipple:
@gdk_renderer:
@part:
@color:
@void:
@Returns:
@screen:
@Returns:
A Pango text attribute containing a embossed bitmap to be used when
rendering the text.
@attr: the #PangoAttribute.
@embossed: the embossed bitmap.
A Pango text attribute specifying the color to emboss text with.
@attr: the #PangoAttribute
@color: the color
A Pango text attribute containing a stipple bitmap to be used when
rendering the text.
@attr: the #PangoAttribute.
@stipple: the stipple bitmap.
@color:
@Returns:
@embossed:
@Returns:
@stipple:
@Returns:
@layout:
@x_origin:
@y_origin:
@index_ranges:
@n_ranges:
@Returns:
@line:
@x_origin:
@y_origin:
@index_ranges:
@n_ranges:
@Returns: