cookbook: Added layout introduction and "stacking actors" recipe

Expanded the layout introduction and added a recipe about
stacking actors using ClutterBinLayout, with two examples.

doc/cookbook/examples/layouts-stacking.c

@@ -0,0 +1,80 @@
+/*
+ * Display multiple rotated copies of an image on top of each other
+ *
+ * Invoke with the path to a file to load a custom image
+ */
+#include <clutter/clutter.h>
+
+#define STAGE_SIDE 512
+
+static const ClutterColor box_color = { 0x33, 0x33, 0x55, 0xff };
+
+int
+main (int argc, char *argv[])
+{
+  gchar *filename = TESTS_DATA_DIR "/redhand.png";
+
+  if (argc > 1)
+    filename = argv[1];
+
+  ClutterLayoutManager *layout;
+  ClutterActor *box;
+  ClutterActor *stage;
+  ClutterActor *texture;
+  CoglHandle *cogl_texture;
+  GError *error = NULL;
+  gfloat width;
+
+  clutter_init (&argc, &argv);
+
+  stage = clutter_stage_get_default ();
+  clutter_actor_set_size (stage, STAGE_SIDE, STAGE_SIDE);
+
+  layout = clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_CENTER,
+                                   CLUTTER_BIN_ALIGNMENT_CENTER);
+
+  box = clutter_box_new (layout);
+  clutter_box_set_color (CLUTTER_BOX (box), &box_color);
+
+  texture = clutter_texture_new_from_file (filename, &error);
+
+  if (error != NULL)
+    g_error ("Error loading file %s; message was:\n%s",
+             filename,
+             error->message);
+
+  /*
+   * get a reference to the underlying Cogl texture
+   * for copying onto each Clutter texture placed into the layout
+   */
+  cogl_texture = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (texture));
+
+  /*
+   * add gradually turning and shrinking textures,
+   * smallest one last; each actor ends up on top
+   * of the one added just before it
+   */
+  for (width = STAGE_SIDE * 0.75; width >= STAGE_SIDE * 0.0625; width -= STAGE_SIDE * 0.0625)
+    {
+      ClutterActor *texture_copy = clutter_texture_new ();
+      clutter_texture_set_cogl_texture (CLUTTER_TEXTURE (texture_copy),
+                                        cogl_texture);
+      clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (texture_copy),
+                                             TRUE);
+      clutter_actor_set_z_rotation_from_gravity (texture_copy,
+                                                 (gfloat)(width * 0.5) - (STAGE_SIDE * 0.03125),
+                                                 CLUTTER_GRAVITY_CENTER);
+      clutter_actor_set_width (texture_copy, width);
+      clutter_container_add_actor (CLUTTER_CONTAINER (box), texture_copy);
+    }
+
+  clutter_actor_add_constraint (box, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
+  clutter_actor_add_constraint (box, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.5));
+  clutter_container_add_actor (CLUTTER_CONTAINER (stage), box);
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  return 0;
+}