cookbook: Added example to show how stacking affects pointer events

Added another example (used for a screenshot) to demonstrate
how pointer events pass through non-reactive actors and how
depth ordering affects whether an actor will emit a pointer
motion signal.

doc/cookbook/examples/Makefile.am

@@ -13,6 +13,7 @@ noinst_PROGRAMS = \
 	events-mouse-scroll \
 	events-pointer-motion	\
 	events-pointer-motion-crossing	\
+	events-pointer-motion-stacked	\
 	events-pointer-motion-scribbler	\
 	$(NULL)
 
@@ -45,6 +46,7 @@ layouts_stacking_diff_sized_actors_SOURCES = layouts-stacking-diff-sized-actors.
 events_mouse_scroll_SOURCES                = events-mouse-scroll.c
 events_pointer_motion_SOURCES              = events-pointer-motion.c
 events_pointer_motion_crossing_SOURCES     = events-pointer-motion-crossing.c
+events_pointer_motion_stacked_SOURCES      = events-pointer-motion-stacked.c
 events_pointer_motion_scribbler_SOURCES    = events-pointer-motion-scribbler.c
 
 -include $(top_srcdir)/build/autotools/Makefile.am.gitignore

doc/cookbook/examples/events-pointer-motion-stacked.c

@@ -0,0 +1,90 @@
+/*
+ * Testing what happens with a stack of actors and pointer events
+ * red and green are reactive; blue is not
+ *
+ * when the pointer is over green (even if green is obscured by blue)
+ * signals are emitted by green (not by blue);
+ *
+ * but when the pointer is over the overlap between red and green,
+ * signals are emitted by green
+ *
+ * gcc -g -O0 -o stacked-actors-and-events stacked-actors-and-events.c `pkg-config --libs --cflags clutter-1.0 glib-2.0` -lm
+ */
+#include <clutter/clutter.h>
+
+static const ClutterColor stage_color = { 0x33, 0x33, 0x55, 0xff };
+static const ClutterColor red = { 0xff, 0x00, 0x00, 0xff };
+static const ClutterColor green = { 0x00, 0xff, 0x00, 0xff };
+static const ClutterColor blue = { 0x00, 0x00, 0xff, 0xff };
+
+static gboolean
+_pointer_motion_cb (ClutterActor *actor,
+                    ClutterEvent *event,
+                    gpointer      user_data)
+{
+  /* get the coordinates where the pointer crossed into the actor */
+  gfloat stage_x, stage_y;
+  clutter_event_get_coords (event, &stage_x, &stage_y);
+
+  /*
+   * as the coordinates are relative to the stage, rather than
+   * the actor which emitted the signal, it can be useful to
+   * transform them to actor-relative coordinates
+   */
+  gfloat actor_x, actor_y;
+  clutter_actor_transform_stage_point (actor,
+                                       stage_x, stage_y,
+                                       &actor_x, &actor_y);
+
+  g_debug ("pointer on actor %s @ x %.0f, y %.0f",
+           clutter_actor_get_name (actor),
+           actor_x, actor_y);
+
+  return TRUE;
+}
+
+int
+main (int argc, char *argv[])
+{
+  ClutterActor *stage;
+  ClutterActor *r1, *r2, *r3;
+
+  clutter_init (&argc, &argv);
+
+  stage = clutter_stage_get_default ();
+  clutter_actor_set_size (stage, 300, 300);
+  clutter_stage_set_color (CLUTTER_STAGE (stage), &stage_color);
+
+  r1 = clutter_rectangle_new_with_color (&red);
+  clutter_actor_set_size (r1, 150, 150);
+  clutter_actor_add_constraint (r1, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.25));
+  clutter_actor_add_constraint (r1, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.25));
+  clutter_actor_set_reactive (r1, TRUE);
+  clutter_actor_set_name (r1, "red");
+
+  r2 = clutter_rectangle_new_with_color (&green);
+  clutter_actor_set_size (r2, 150, 150);
+  clutter_actor_add_constraint (r2, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.5));
+  clutter_actor_add_constraint (r2, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.5));
+  clutter_actor_set_reactive (r2, TRUE);
+  clutter_actor_set_depth (r2, -100);
+  clutter_actor_set_name (r2, "green");
+
+  r3 = clutter_rectangle_new_with_color (&blue);
+  clutter_actor_set_size (r3, 150, 150);
+  clutter_actor_add_constraint (r3, clutter_align_constraint_new (stage, CLUTTER_ALIGN_X_AXIS, 0.75));
+  clutter_actor_add_constraint (r3, clutter_align_constraint_new (stage, CLUTTER_ALIGN_Y_AXIS, 0.75));
+  clutter_actor_set_opacity (r3, 125.5);
+  clutter_actor_set_name (r3, "blue");
+
+  clutter_container_add (CLUTTER_CONTAINER (stage), r1, r2, r3, NULL);
+
+  g_signal_connect (r1, "motion-event", G_CALLBACK (_pointer_motion_cb), NULL);
+  g_signal_connect (r2, "motion-event", G_CALLBACK (_pointer_motion_cb), NULL);
+
+  clutter_actor_show (stage);
+
+  clutter_main ();
+
+  return 0;
+}