Add rounded corners rectangle example using Canvas

An old request: how to create a rectangle with rounded corners with
Clutter; we use ClutterCanvas and Cairo because we want anti-aliased
edges.

examples/Makefile.am

@@ -9,6 +9,7 @@ all_examples = \
 	drop-action \
 	easing-modes \
 	flow-layout \
+	rounded-rectangle \
 	threads
 
 if PIXBUF_TESTS

examples/rounded-rectangle.c

@@ -0,0 +1,107 @@
+#include <stdlib.h>
+#include <math.h>
+#include <cairo.h>
+#include <clutter/clutter.h>
+
+static gboolean
+draw_content (ClutterCanvas *canvas,
+              cairo_t       *cr,
+              int            surface_width,
+              int            surface_height)
+{
+  /* rounded rectangle taken from:
+   *
+   *   http://cairographics.org/samples/rounded_rectangle/
+   *
+   * we leave 1 pixel around the edges to avoid jagged edges
+   * when rotating the actor
+   */
+  double x             = 1.0,        /* parameters like cairo_rectangle */
+         y             = 1.0,
+         width         = surface_width - 2.0,
+         height        = surface_height - 2.0,
+         aspect        = 1.0,     /* aspect ratio */
+         corner_radius = height / 20.0;   /* and corner curvature radius */
+
+  double radius = corner_radius / aspect;
+  double degrees = M_PI / 180.0;
+
+  cairo_save (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
+  cairo_paint (cr);
+  cairo_restore (cr);
+
+  cairo_new_sub_path (cr);
+  cairo_arc (cr, x + width - radius, y + radius, radius, -90 * degrees, 0 * degrees);
+  cairo_arc (cr, x + width - radius, y + height - radius, radius, 0 * degrees, 90 * degrees);
+  cairo_arc (cr, x + radius, y + height - radius, radius, 90 * degrees, 180 * degrees);
+  cairo_arc (cr, x + radius, y + radius, radius, 180 * degrees, 270 * degrees);
+  cairo_close_path (cr);
+
+  cairo_set_source_rgb (cr, 0.5, 0.5, 1);
+  cairo_fill (cr);
+
+  /* we're done drawing */
+  return TRUE;
+}
+
+int
+main (int argc, char *argv[])
+{
+  ClutterActor *stage, *actor;
+  ClutterContent *canvas;
+  ClutterTransition *transition;
+
+  /* initialize Clutter */
+  if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
+    return EXIT_FAILURE;
+
+  /* create a stage */
+  stage = clutter_stage_new ();
+  clutter_stage_set_title (CLUTTER_STAGE (stage), "Rectangle with rounded corners");
+  clutter_actor_set_background_color (stage, CLUTTER_COLOR_Black);
+  clutter_actor_set_size (stage, 500, 500);
+  clutter_actor_show (stage);
+
+  /* our 2D canvas, courtesy of Cairo */
+  canvas = clutter_canvas_new ();
+  clutter_canvas_set_size (CLUTTER_CANVAS (canvas), 300, 300);
+
+  /* the actor that will display the contents of the canvas */
+  actor = clutter_actor_new ();
+  clutter_actor_set_content (actor, canvas);
+  clutter_actor_set_content_gravity (actor, CLUTTER_CONTENT_GRAVITY_CENTER);
+  clutter_actor_set_content_scaling_filters (actor,
+                                             CLUTTER_SCALING_FILTER_TRILINEAR,
+                                             CLUTTER_SCALING_FILTER_LINEAR);
+  clutter_actor_set_rotation (actor, CLUTTER_Y_AXIS, 0.0, 250.f, 0.f, 0.f);
+  clutter_actor_add_constraint (actor, clutter_bind_constraint_new (stage, CLUTTER_BIND_SIZE, 0.f));
+  clutter_actor_add_child (stage, actor);
+
+  /* the actor now owns the canvas */
+  g_object_unref (canvas);
+
+  /* create the continuous animation of the actor spinning around its center */
+  transition = clutter_property_transition_new ("rotation-angle-y");
+  clutter_transition_set_from (transition, G_TYPE_DOUBLE, 0.0);
+  clutter_transition_set_to (transition, G_TYPE_DOUBLE, 360.0);
+  clutter_timeline_set_duration (CLUTTER_TIMELINE (transition), 2000);
+  clutter_timeline_set_repeat_count (CLUTTER_TIMELINE (transition), -1);
+  clutter_actor_add_transition (actor, "rotateActor", transition);
+
+  /* the actor now owns the transition */
+  g_object_unref (transition);
+
+  /* quit on destroy */
+  g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
+
+  /* connect our drawing code */
+  g_signal_connect (canvas, "draw", G_CALLBACK (draw_content), NULL);
+
+  /* invalidate the canvas, so that we can draw before the main loop starts */
+  clutter_content_invalidate (canvas);
+
+  clutter_main ();
+
+  return EXIT_SUCCESS;
+}