Add ShellDrawingArea and ShellStack

ShellDrawingArea is a size-independent wrapper for a ClutterCairoTexture.
Useful when drawing non-fixed size areas.

ShellStack is a simple container class which holds items
in a completely overlapping Z stack.  The main difference
from ClutterGroup is that items will be constrained to
(and allocated) the size of the stack, not getting their
preferred size always.

src/shell-stack.c

@@ -0,0 +1,152 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/**
+ * SECTION:shell-stack
+ * @short_description: Pure "Z-axis" container class
+ *
+ * A #ShellStack draws its children on top of each other,
+ * aligned to the top left.  It will be sized in width/height
+ * according to the largest such dimension of its children, and
+ * all children will be allocated that size.  This differs
+ * from #ClutterGroup which allocates its children their natural
+ * size, even if that would overflow the size allocated to the stack.
+ */
+
+#include "shell-stack.h"
+
+G_DEFINE_TYPE (ShellStack,
+               shell_stack,
+               CLUTTER_TYPE_GROUP);
+
+static void
+shell_stack_allocate (ClutterActor           *self,
+                      const ClutterActorBox  *box,
+                      ClutterAllocationFlags  flags)
+{
+  ClutterGroupPrivate *priv = CLUTTER_GROUP (self)->priv;
+  GList *children, *iter;
+
+  /* chain up to set actor->allocation */
+  (CLUTTER_ACTOR_CLASS (g_type_class_peek (clutter_actor_get_type ())))->allocate (self, box, flags);
+
+  children = clutter_container_get_children (CLUTTER_CONTAINER (self));
+  for (iter = children; iter; iter = iter->next)
+    {
+      ClutterActor *actor = CLUTTER_ACTOR (iter->data);
+      clutter_actor_allocate (actor, box, flags);
+    }
+  g_list_free (children);
+}
+
+static void
+shell_stack_get_preferred_height (ClutterActor *actor,
+                                  gfloat for_width,
+                                  gfloat *min_height_p,
+                                  gfloat *natural_height_p)
+{
+  ShellStack *stack = SHELL_STACK (actor);
+  gboolean first = TRUE;
+  float min = 0, natural = 0;
+  GList *children;
+  GList *iter;
+
+  children = clutter_container_get_children (CLUTTER_CONTAINER (stack));
+
+  for (iter = children; iter; iter = iter->next)
+    {
+      ClutterActor *child = iter->data;
+      float child_min, child_natural;
+
+      clutter_actor_get_preferred_height (child,
+                                          for_width,
+                                          &child_min,
+                                          &child_natural);
+
+      if (first)
+        {
+          first = FALSE;
+          min = child_min;
+          natural = child_natural;
+        }
+      else
+        {
+          if (child_min > min)
+            min = child_min;
+
+          if (child_natural > natural)
+            natural = child_natural;
+        }
+    }
+
+  if (min_height_p)
+    *min_height_p = min;
+
+  if (natural_height_p)
+    *natural_height_p = natural;
+
+  g_list_free (children);
+}
+
+static void
+shell_stack_get_preferred_width (ClutterActor *actor,
+                                 gfloat for_height,
+                                 gfloat *min_width_p,
+                                 gfloat *natural_width_p)
+{
+  ShellStack *stack = SHELL_STACK (actor);
+  gboolean first = TRUE;
+  float min = 0, natural = 0;
+  GList *iter;
+  GList *children;
+
+  children = clutter_container_get_children (CLUTTER_CONTAINER (stack));
+
+  for (iter = children; iter; iter = iter->next)
+    {
+      ClutterActor *child = iter->data;
+      float child_min, child_natural;
+
+      clutter_actor_get_preferred_width (child,
+                                         for_height,
+                                         &child_min,
+                                         &child_natural);
+
+      if (first)
+        {
+          first = FALSE;
+          min = child_min;
+          natural = child_natural;
+        }
+      else
+        {
+          if (child_min > min)
+            min = child_min;
+
+          if (child_natural > natural)
+            natural = child_natural;
+        }
+    }
+
+  if (min_width_p)
+    *min_width_p = min;
+
+  if (natural_width_p)
+    *natural_width_p = natural;
+  g_list_free (children);
+}
+
+static void
+shell_stack_class_init (ShellStackClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+  ClutterActorClass *actor_class = CLUTTER_ACTOR_CLASS (klass);
+
+  actor_class->get_preferred_width = shell_stack_get_preferred_width;
+  actor_class->get_preferred_height = shell_stack_get_preferred_height;
+  actor_class->allocate = shell_stack_allocate;
+}
+
+static void
+shell_stack_init (ShellStack *actor)
+{
+}