[ClutterGroup] Don't take into account the left edges when calculating the size

ClutterGroup previously calculated the size as the distance from the
left edge of the leftmost child to the right edge of the rightmost
child except if there were any chidren left of the origin then the
left edge would be zero.

However the group is always allocated its size relative to its
origin so if all of the children are to the right of the origin then
the preferred size would not be large enough to reach the rightmost
child.

    origin
    ┼──────────┐
    │Group     │
    │ ┌────────┼─┐
    │ │Child   │ │
    │ │        │ │
    └─┼────────┘ │
      │          │
      └──────────┘
       group size
      ╟──────────╢

This patch makes it so the size is always just the rightmost edge.

    origin
    ┼────────────┐
    │Group       │
    │ ┌──────────┤
    │ │Child     │
    │ │          │
    │ │          │
    │ │          │
    └─┴──────────┘
      group size
    ╟────────────╢

Fixes bug:

  http://bugzilla.openedhand.com/show_bug.cgi?id=1825

clutter/clutter-group.c

@@ -132,12 +132,11 @@ clutter_fixed_layout_get_preferred_width (GList  *children,
                                           gfloat *natural_width_p)
 {
   GList *l;
-  gdouble min_left, min_right;
+  gdouble min_right, natural_right;
-  gdouble natural_left, natural_right;
 
-  min_left = 0;
+  /* We will always be at least 0 sized (ie, if all of the actors are
+     to the left of the origin we won't return a negative size) */
   min_right = 0;
-  natural_left = 0;
   natural_right = 0;
 
   for (l = children; l != NULL; l = l->next)
@@ -151,55 +150,21 @@ clutter_fixed_layout_get_preferred_width (GList  *children,
                                         &child_min, NULL,
                                         &child_natural, NULL);
 
-      if (l == children)
+      /* Track the rightmost edge */
-        {
-          /* First child */
-          min_left = child_x;
-          natural_left = child_x;
-          min_right = min_left + child_min;
-          natural_right = natural_left + child_natural;
-        }
-      else
-        {
-          /* Union of extents with previous children */
-          if (child_x < min_left)
-            min_left = child_x;
-
-          if (child_x < natural_left)
-            natural_left = child_x;
-
       if (child_x + child_min > min_right)
         min_right = child_x + child_min;
 
       if (child_x + child_natural > natural_right)
         natural_right = child_x + child_natural;
     }
-    }
-
-  /* The preferred size is defined as the width and height we want starting
-   * from our origin, since our allocation will set the origin; so we now
-   * need to remove any part of the request that is to the left of the origin.
-   */
-  if (min_left < 0)
-    min_left = 0;
-
-  if (natural_left < 0)
-    natural_left = 0;
-
-  if (min_right < 0)
-    min_right = 0;
-
-  if (natural_right < 0)
-    natural_right = 0;
-
-  g_assert (min_right >= min_left);
-  g_assert (natural_right >= natural_left);
 
+  /* The size is defined as the distance from the origin to the
+     right-hand edge of the rightmost actor */
   if (min_width_p)
-    *min_width_p = min_right - min_left;
+    *min_width_p = min_right;
 
   if (natural_width_p)
-    *natural_width_p = natural_right - min_left;
+    *natural_width_p = natural_right;
 }
 
 static void
@@ -208,12 +173,11 @@ clutter_fixed_layout_get_preferred_height (GList  *children,
                                            gfloat *natural_height_p)
 {
   GList *l;
-  gdouble min_top, min_bottom;
+  gdouble min_bottom, natural_bottom;
-  gdouble natural_top, natural_bottom;
 
-  min_top = 0;
+  /* We will always be at least 0 sized (ie, if all of the actors are
+     above the origin we won't return a negative size) */
   min_bottom = 0;
-  natural_top = 0;
   natural_bottom = 0;
 
   for (l = children; l != NULL; l = l->next)
@@ -227,55 +191,21 @@ clutter_fixed_layout_get_preferred_height (GList  *children,
                                         NULL, &child_min,
                                         NULL, &child_natural);
 
-      if (l == children)
+      /* Track the bottommost edge */
-        {
-          /* First child */
-          min_top = child_y;
-          natural_top = child_y;
-          min_bottom = min_top + child_min;
-          natural_bottom = natural_top + child_natural;
-        }
-      else
-        {
-          /* Union of extents with previous children */
-          if (child_y < min_top)
-            min_top = child_y;
-
-          if (child_y < natural_top)
-            natural_top = child_y;
-
       if (child_y + child_min > min_bottom)
         min_bottom = child_y + child_min;
 
       if (child_y + child_natural > natural_bottom)
         natural_bottom = child_y + child_natural;
     }
-    }
-
-  /* The preferred size is defined as the width and height we want starting
-   * from our origin, since our allocation will set the origin; so we now
-   * need to remove any part of the request that is above the origin.
-   */
-  if (min_top < 0)
-    min_top = 0;
-
-  if (natural_top < 0)
-    natural_top = 0;
-
-  if (min_bottom < 0)
-    min_bottom = 0;
-
-  if (natural_bottom < 0)
-    natural_bottom = 0;
-
-  g_assert (min_bottom >= min_top);
-  g_assert (natural_bottom >= natural_top);
 
+  /* The size is defined as the distance from the origin to the bottom
+     edge of the bottommost actor */
   if (min_height_p)
-    *min_height_p = min_bottom - min_top;
+    *min_height_p = min_bottom;
 
   if (natural_height_p)
-    *natural_height_p = natural_bottom - min_top;
+    *natural_height_p = natural_bottom;
 }
 
 static void