cookbook: Added a longer slideshow example

Cross-fading between two images is straightforward,
but cycling between more than two is more efficient
if done by copying COGL textures between the
two textures, rather than trying to reposition the
textures.

The example demonstrates how to reuse a pair of
textures to cycle through multiple images.

doc/cookbook/examples/Makefile.am

@@ -13,6 +13,7 @@ noinst_PROGRAMS = \
 	events-mouse-scroll \
 	textures-crossfade	\
 	textures-crossfade-cogl	\
+	textures-crossfade-slideshow	\
 	$(NULL)
 
 INCLUDES = \
@@ -44,5 +45,6 @@ layouts_stacking_diff_sized_actors_SOURCES = layouts-stacking-diff-sized-actors.
 events_mouse_scroll_SOURCES                = events-mouse-scroll.c
 textures_crossfade_SOURCES                 = textures-crossfade.c
 textures_crossfade_cogl_SOURCES            = textures-crossfade-cogl.c
+textures_crossfade_slideshow_SOURCES       = textures-crossfade-slideshow.c
 
 -include $(top_srcdir)/build/autotools/Makefile.am.gitignore

doc/cookbook/examples/textures-crossfade-slideshow.c

@@ -0,0 +1,182 @@
+/*
+ * Simple slideshow application, cycling images between
+ * two ClutterTextures
+ *
+ * Run by passing one or more image paths or directory globs
+ * which will pick up image files
+ *
+ * When running, press any key to go to the next image
+ */
+#include <stdlib.h>
+#include <clutter/clutter.h>
+
+static guint stage_side = 600;
+static guint animation_duration_ms = 1500;
+
+static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
+
+typedef struct {
+  ClutterActor *front;
+  ClutterActor *back;
+  ClutterState *transitions;
+  GSList       *image_paths;
+  guint         next_image_index;
+} State;
+
+static gboolean
+load_next_image (State *app)
+{
+  /* don't do anything if already animating */
+  ClutterTimeline *timeline = clutter_state_get_timeline (app->transitions);
+
+  if (clutter_timeline_is_playing (timeline) == 1)
+    {
+      g_debug ("Animation is running already");
+      return FALSE;
+    }
+
+  if (!app->next_image_index)
+      app->next_image_index = 0;
+
+  gpointer next = g_slist_nth_data (app->image_paths, app->next_image_index);
+
+  if (next == NULL)
+    return FALSE;
+
+  gchar *image_path = (gchar *)next;
+
+  g_debug ("Loading %s", image_path);
+
+  CoglHandle *cogl_texture;
+  cogl_texture = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (app->front));
+
+  if (cogl_texture != NULL)
+    {
+      /* copy the current texture into the background */
+      clutter_texture_set_cogl_texture (CLUTTER_TEXTURE (app->back), cogl_texture);
+
+      /* make the back opaque and front transparent */
+      clutter_state_warp_to_state (app->transitions, "show-back");
+    }
+
+  /* load the next image into the front */
+  GError *error = NULL;
+  clutter_texture_set_from_file (CLUTTER_TEXTURE (app->front),
+                                 image_path,
+                                 &error);
+
+  if (error != NULL)
+    {
+      g_warning ("Error loading %s\n%s", image_path, error->message);
+      g_error_free (error);
+      return FALSE;
+    }
+
+  /* fade in the front texture and fade out the back texture */
+  clutter_state_set_state (app->transitions, "show-front");
+
+  app->next_image_index++;
+
+  return TRUE;
+}
+
+static gboolean
+_key_pressed_cb (ClutterActor *actor,
+                 ClutterEvent *event,
+                 gpointer      user_data)
+{
+  State *app = (State *)user_data;
+
+  load_next_image (app);
+
+  return TRUE;
+}
+
+int
+main (int argc, char *argv[])
+{
+  if (argc < 2)
+    {
+      g_print ("Usage: %s <image paths to load>\n", argv[0]);
+      exit (EXIT_FAILURE);
+    }
+
+  State *app = g_new0 (State, 1);
+  app->image_paths = NULL;
+
+  /*
+   * NB if your shell globs arguments to this program so argv
+   * includes non-image files, they will fail to load and throw errors
+   */
+  guint i;
+  for (i = 1; i < argc; i++)
+    app->image_paths = g_slist_append (app->image_paths, argv[i]);
+
+  GError *error = NULL;
+
+  /* UI */
+  ClutterActor *stage;
+  ClutterLayoutManager *layout;
+  ClutterActor *box;
+
+  clutter_init (&argc, &argv);
+
+  stage = clutter_stage_get_default ();
+  g_signal_connect (stage, "destroy", G_CALLBACK (clutter_main_quit), NULL);
+  clutter_stage_set_title (CLUTTER_STAGE (stage), "cross-fade");
+  clutter_actor_set_size (stage, stage_side, stage_side);
+  clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
+
+  layout = clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_CENTER,
+                                   CLUTTER_BIN_ALIGNMENT_CENTER);
+
+  box = clutter_box_new (layout);
+  clutter_actor_set_size (box, stage_side, stage_side);
+
+  app->back = clutter_texture_new ();
+  clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (app->back), TRUE);
+
+  app->front = clutter_texture_new ();
+  clutter_texture_set_keep_aspect_ratio (CLUTTER_TEXTURE (app->front), TRUE);
+
+  clutter_container_add_actor (CLUTTER_CONTAINER (box), app->back);
+  clutter_container_add_actor (CLUTTER_CONTAINER (box), app->front);
+  clutter_container_add_actor (CLUTTER_CONTAINER (stage), box);
+
+  /* animations */
+  app->transitions = clutter_state_new ();
+  clutter_state_set (app->transitions, NULL, "show-front",
+                     app->front, "opacity", CLUTTER_EASE_IN_CUBIC, 255,
+                     app->back, "opacity", CLUTTER_EASE_IN_CUBIC, 0,
+                     NULL);
+  clutter_state_set (app->transitions, NULL, "show-back",
+                     app->front, "opacity", CLUTTER_LINEAR, 0,
+                     app->back, "opacity", CLUTTER_LINEAR, 255,
+                     NULL);
+  clutter_state_set_duration (app->transitions,
+                              NULL,
+                              NULL,
+                              animation_duration_ms);
+
+  /* display the next (first) image */
+  load_next_image (app);
+
+  /* key press displays the next image */
+  g_signal_connect (stage,
+                    "key-press-event",
+                    G_CALLBACK (_key_pressed_cb),
+                    app);
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  g_slist_free (app->image_paths);
+  g_object_unref (app->transitions);
+  g_free (app);
+
+  if (error != NULL)
+    g_error_free (error);
+
+  return EXIT_SUCCESS;
+}