Move scroll actor test to the examples

Nothing specific to test, and the code is idiomatic enough to be used as
an example.

examples/Makefile.am

@@ -10,6 +10,7 @@ all_examples = \
 	flow-layout \
 	layout-manager \
 	rounded-rectangle \
+	scroll-actor \
 	threads
 
 if PIXBUF_TESTS

examples/scroll-actor.c

@@ -0,0 +1,193 @@
+#include <stdlib.h>
+#include <glib.h>
+#include <clutter/clutter.h>
+
+static const char *menu_items_name[] = {
+  "Option 1",
+  "Option 2",
+  "Option 3",
+  "Option 4",
+  "Option 5",
+  "Option 6",
+  "Option 7",
+  "Option 8",
+  "Option 9",
+  "Option 10",
+  "Option 11",
+};
+
+static const guint menu_items_len = G_N_ELEMENTS (menu_items_name);
+
+static void
+select_item_at_index (ClutterActor *scroll, 
+                      int           index_)
+{
+  ClutterPoint point;
+  ClutterActor *menu, *item;
+  gpointer old_selected;
+
+  menu = clutter_actor_get_first_child (scroll);
+
+  old_selected = g_object_get_data (G_OBJECT (scroll), "selected-item");
+  if (old_selected != NULL)
+    {
+      item = clutter_actor_get_child_at_index (menu, GPOINTER_TO_INT (old_selected));
+      clutter_text_set_color (CLUTTER_TEXT (item), CLUTTER_COLOR_White);
+    }
+
+  /* wrap around the index */
+  if (index_ < 0)
+    index_ = clutter_actor_get_n_children (menu) - 1;
+  else if (index_ >= clutter_actor_get_n_children (menu))
+    index_ = 0;
+
+  item = clutter_actor_get_child_at_index (menu, index_);
+  clutter_actor_get_position (item, &point.x, &point.y);
+
+  /* scroll to the actor's position; the menu actor is always set at (0, 0),
+   * so it does not contribute any further offset, and we can use the position
+   * of its children to ask the ScrollActor to scroll the visible region; if
+   * the menu actor had an offset, or was transformed, we would have needed to
+   * get their relative transformed position instead.
+   */
+  clutter_actor_save_easing_state (scroll);
+  clutter_scroll_actor_scroll_to_point (CLUTTER_SCROLL_ACTOR (scroll), &point);
+  clutter_actor_restore_easing_state (scroll);
+
+  clutter_text_set_color (CLUTTER_TEXT (item), CLUTTER_COLOR_LightSkyBlue);
+
+  /* store the index of the currently selected item, so that we can
+   * implement select_next_item() and select_prev_item()
+   */
+  g_object_set_data (G_OBJECT (scroll), "selected-item",
+                     GINT_TO_POINTER (index_));
+}
+
+static void
+select_next_item (ClutterActor *scroll)
+{
+  gpointer selected_ = g_object_get_data (G_OBJECT (scroll), "selected-item");
+
+  select_item_at_index (scroll, GPOINTER_TO_INT (selected_) + 1);
+}
+
+static void
+select_prev_item (ClutterActor *scroll)
+{
+  gpointer selected_ = g_object_get_data (G_OBJECT (scroll), "selected-item");
+
+  select_item_at_index (scroll, GPOINTER_TO_INT (selected_) - 1);
+}
+
+static ClutterActor *
+create_menu_item (const char *name)
+{
+  ClutterActor *text;
+
+  text = clutter_text_new ();
+  clutter_text_set_font_name (CLUTTER_TEXT (text), "Sans Bold 24");
+  clutter_text_set_text (CLUTTER_TEXT (text), name);
+  clutter_text_set_color (CLUTTER_TEXT (text), CLUTTER_COLOR_White);
+  clutter_actor_set_margin_left (text, 12.f);
+  clutter_actor_set_margin_right (text, 12.f);
+
+  return text;
+}
+
+static ClutterActor *
+create_menu_actor (ClutterActor *scroll)
+{
+  ClutterActor *menu;
+  ClutterLayoutManager *layout_manager;
+  guint i;
+
+  /* this is our menu; it contains items in a vertical layout */
+  layout_manager = clutter_box_layout_new ();
+  clutter_box_layout_set_orientation (CLUTTER_BOX_LAYOUT (layout_manager),
+                                      CLUTTER_ORIENTATION_VERTICAL);
+  clutter_box_layout_set_spacing (CLUTTER_BOX_LAYOUT (layout_manager), 12.f);
+
+  menu = clutter_actor_new ();
+  clutter_actor_set_layout_manager (menu, layout_manager);
+  clutter_actor_set_background_color (menu, CLUTTER_COLOR_Black);
+
+  /* these are the items */
+  for (i = 0; i < menu_items_len; i++)
+    clutter_actor_add_child (menu, create_menu_item (menu_items_name[i]));
+
+  return menu;
+}
+
+static ClutterActor *
+create_scroll_actor (ClutterActor *stage)
+{
+  ClutterActor *scroll;
+
+  /* our scrollable viewport */
+  scroll = clutter_scroll_actor_new ();
+  clutter_actor_set_name (scroll, "scroll");
+
+  /* give a vertical offset, and constrain the viewport so that its size
+   * is bound to the stage size
+   */
+  clutter_actor_set_position (scroll, 0.f, 18.f);
+  clutter_actor_add_constraint (scroll, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
+  clutter_actor_add_constraint (scroll, clutter_bind_constraint_new (stage, CLUTTER_BIND_HEIGHT, -36.f));
+
+  /* we only want to scroll the contents vertically, and
+   * ignore any horizontal component
+   */
+  clutter_scroll_actor_set_scroll_mode (CLUTTER_SCROLL_ACTOR (scroll),
+                                        CLUTTER_SCROLL_VERTICALLY);
+
+  clutter_actor_add_child (scroll, create_menu_actor (scroll));
+
+  /* select the first item */
+  select_item_at_index (scroll, 0);
+
+  return scroll;
+}
+
+static gboolean
+on_key_press (ClutterActor *stage,
+              ClutterEvent *event,
+              gpointer      unused)
+{
+  ClutterActor *scroll;
+  guint key_symbol;
+
+  scroll = clutter_actor_get_first_child (stage);
+
+  key_symbol = clutter_event_get_key_symbol (event);
+
+  if (key_symbol == CLUTTER_KEY_Up)
+    select_prev_item (scroll);
+  else if (key_symbol == CLUTTER_KEY_Down)
+    select_next_item (scroll);
+
+  return CLUTTER_EVENT_STOP;
+}
+
+int
+main (int argc, char *argv[])
+{
+  ClutterActor *stage;
+
+  if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
+    return EXIT_FAILURE;
+
+  /* create a new stage */
+  stage = clutter_stage_new ();
+  clutter_stage_set_title (CLUTTER_STAGE (stage), "Scroll Actor");
+  clutter_stage_set_user_resizable (CLUTTER_STAGE (stage), TRUE);
+  g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
+  g_signal_connect (stage, "key-press-event", G_CALLBACK (on_key_press), NULL);
+
+  clutter_actor_add_child (stage, create_scroll_actor (stage));
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  return EXIT_SUCCESS;
+}