docs: Add recipe for animating an actor on a curved path

Show how to animate an actor using a ClutterPathConstraint.

This demonstrates how to get effects similar to
ClutterPathBehaviour with the modern animation APIs.

Includes 3 examples:

1) Simple ClutterPathConstraint used with implicit animations
2) ClutterPathConstraint used to simulate circular animation,
using ClutterAnimator
3) Creating simple curved path animations with non-linear
easing

doc/cookbook/examples/animations-path-easing.c

@@ -0,0 +1,104 @@
+#include <stdlib.h>
+#include <clutter/clutter.h>
+
+typedef struct {
+  ClutterActor *red;
+  ClutterActor *green;
+  ClutterTimeline *timeline;
+} State;
+
+static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
+static const ClutterColor red_color = { 0xff, 0x00, 0x00, 0xff };
+static const ClutterColor green_color = { 0x00, 0xff, 0x00, 0xff };
+
+static void
+reverse_timeline (ClutterTimeline *timeline)
+{
+  ClutterTimelineDirection dir = clutter_timeline_get_direction (timeline);
+
+  if (dir == CLUTTER_TIMELINE_FORWARD)
+    dir = CLUTTER_TIMELINE_BACKWARD;
+  else
+    dir = CLUTTER_TIMELINE_FORWARD;
+
+  clutter_timeline_set_direction (timeline, dir);
+}
+
+/* a key press either starts the timeline or reverses it */
+static gboolean
+key_pressed_cb (ClutterActor *actor,
+                ClutterEvent *event,
+                gpointer      user_data)
+{
+  State *state = (State *) user_data;
+
+  if (clutter_timeline_is_playing (state->timeline))
+    reverse_timeline (state->timeline);
+  else
+    clutter_timeline_start (state->timeline);
+
+  return TRUE;
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  State *state = g_new0 (State, 1);
+
+  ClutterActor *stage;
+  ClutterAnimator *animator;
+
+  clutter_init (&argc, &argv);
+
+  stage = clutter_stage_new ();
+  clutter_actor_set_size (stage, 400, 400);
+  clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
+  g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
+
+  state->red = clutter_rectangle_new_with_color (&red_color);
+  clutter_actor_set_size (state->red, 100, 100);
+  clutter_actor_set_position (state->red, 300, 300);
+
+  state->green = clutter_rectangle_new_with_color (&green_color);
+  clutter_actor_set_size (state->green, 100, 100);
+  clutter_actor_set_position (state->green, 0, 0);
+
+  animator = clutter_animator_new ();
+  clutter_animator_set_duration (animator, 1000);
+
+  clutter_animator_set (animator,
+                        state->red, "x", CLUTTER_LINEAR, 0.0, 300.0,
+                        state->red, "y", CLUTTER_LINEAR, 0.0, 300.0,
+                        state->red, "x", CLUTTER_LINEAR, 1.0, 0.0,
+                        state->red, "y", CLUTTER_EASE_IN_QUINT, 1.0, 0.0,
+                        NULL);
+
+  clutter_animator_set (animator,
+                        state->green, "x", CLUTTER_LINEAR, 0.0, 0.0,
+                        state->green, "y", CLUTTER_LINEAR, 0.0, 0.0,
+                        state->green, "x", CLUTTER_LINEAR, 1.0, 300.0,
+                        state->green, "y", CLUTTER_EASE_IN_QUINT, 1.0, 300.0,
+                        NULL);
+
+  state->timeline = clutter_animator_get_timeline (animator);
+
+  clutter_timeline_set_auto_reverse (state->timeline, TRUE);
+
+  g_signal_connect (stage,
+                    "key-press-event",
+                    G_CALLBACK (key_pressed_cb),
+                    state);
+
+  clutter_container_add (CLUTTER_CONTAINER (stage), state->red, state->green, NULL);
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  g_object_unref (animator);
+
+  g_free (state);
+
+  return EXIT_SUCCESS;
+}