Override the paint signal of
ClutterText and use the CoglPango API to paint the
PangoLayout of the actor with the color of the
shadow at a given offset.

The ClutterText class provides an actor that transforms the PangoLayout object into an element of the Clutter scene graph. The underlying layout is painted, though, through a subset of the Cogl API, called CoglPango.
It is possible to paint PangoLayout created by a
ClutterText by invoking
cogl_pango_render_layout():
void
cogl_pango_render_layout (PangoLayout *layout,
int x_offset,
int y_offset,
CoglColor *text_color,
int flags);This function will paint the layout at the given offsets using the provided color.
The cogl_pango_render_layout()
function will only work with PangoLayouts created by
Clutter.
Since the shadow of the text is literally the same text but painted
with a different color and at an offset, we can use the
paint signal of ClutterText to paint
the shadow, and then let ClutterText paint its contents on
top:
static void
_text_paint_cb (ClutterActor *actor)
{
ClutterText *text = CLUTTER_TEXT (actor);
/* Get the PangoLayout that the Text actor is going to paint... */
PangoLayout *layout;
layout = clutter_text_get_layout (text);
/* ... Create the color of the shadow... */
/* ... Finally, render the Text layout at a given
* offset using the color of the shadow
*/
cogl_pango_render_layout (layout,
SHADOW_X_OFFSET, SHADOW_Y_OFFSET,
&color, 0);
}Note that we are using the PangoLayout of the
ClutterText because the ClutterText actor
always keeps an updated layout internally. It is, however, possible for
any ClutterActor to create a PangoLayout using
clutter_actor_create_pango_layout(), and then paint
that layout using cogl_pango_render_layout() in
their implementation of the paint virtual
function.
Example 6.1. Creating a shadow of a text
#include <stdlib.h>
#include <cogl/cogl.h>
#include <cogl-pango/cogl-pango.h>
#include <clutter/clutter.h>
#define SHADOW_X_OFFSET 3
#define SHADOW_Y_OFFSET 3
static void
_text_paint_cb (ClutterActor *actor)
{
PangoLayout *layout;
guint8 real_opacity;
CoglColor color;
ClutterText *text = CLUTTER_TEXT (actor);
ClutterColor text_color = { 0, };
/* Get the PangoLayout that the Text actor is going to paint */
layout = clutter_text_get_layout (text);
/* Get the color of the text, to extract the alpha component */
clutter_text_get_color (text, &text_color);
/* Composite the opacity so that the shadow is correctly blended */
real_opacity = clutter_actor_get_paint_opacity (actor)
* text_color.alpha
/ 255;
/* Create a #ccc color and premultiply it */
cogl_color_init_from_4ub (&color, 0xcc, 0xcc, 0xcc, real_opacity);
cogl_color_premultiply (&color);
/* Finally, render the Text layout at a given offset using the color */
cogl_pango_render_layout (layout, SHADOW_X_OFFSET, SHADOW_Y_OFFSET, &color, 0);
}
int
main (int argc, char *argv[])
{
ClutterActor *stage;
ClutterActor *text;
if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
return 1;
stage = clutter_stage_new ();
clutter_stage_set_title (CLUTTER_STAGE (stage), "Text shadow");
g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
text = clutter_text_new ();
clutter_text_set_text (CLUTTER_TEXT (text), "Hello, World!");
clutter_text_set_font_name (CLUTTER_TEXT (text), "Sans 64px");
clutter_actor_add_constraint (text, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
clutter_actor_add_constraint (text, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.5));
g_signal_connect (text, "paint", G_CALLBACK (_text_paint_cb), NULL);
clutter_container_add (CLUTTER_CONTAINER (stage), text, NULL);
clutter_actor_show (stage);
clutter_main ();
return EXIT_SUCCESS;
}