Index: gegl/operation/gegl-operation-area-filter.c
===================================================================
--- gegl/operation/gegl-operation-area-filter.c	(revision 1801)
+++ gegl/operation/gegl-operation-area-filter.c	(working copy)
@@ -32,7 +32,7 @@ static GeglRectangle compute_input_reque
                                               const GeglRectangle *region);
 static GeglRectangle compute_affected_region (GeglOperation       *operation,
                                               const gchar         *input_pad,
-                                              GeglRectangle        region);
+                                              const GeglRectangle *region);
 
 static void
 gegl_operation_area_filter_class_init (GeglOperationAreaFilterClass *klass)
@@ -93,7 +93,7 @@ compute_input_request (GeglOperation    
   gegl_rectangle_intersect (&rect, region, &defined);
 
   if (rect.width  != 0 &&
-      rect.height  != 0)
+      rect.height != 0)
     {
       rect.x -= area->left;
       rect.y -= area->top;
@@ -105,15 +105,17 @@ compute_input_request (GeglOperation    
 }
 
 static GeglRectangle
-compute_affected_region (GeglOperation *operation,
-                     const gchar   *input_pad,
-                     GeglRectangle  region)
+compute_affected_region (GeglOperation       *operation,
+                         const gchar         *input_pad,
+                         const GeglRectangle *region)
 {
   GeglOperationAreaFilter *area = GEGL_OPERATION_AREA_FILTER (operation);
+  GeglRectangle            retval;
+
+  retval.x      = region->x - area->left;
+  retval.y      = region->y - area->top;
+  retval.width  = region->width  + area->left + area->right;
+  retval.height = region->height + area->top  + area->bottom;
 
-  region.x -= area->left;
-  region.y -= area->top;
-  region.width  += area->left + area->right;
-  region.height  += area->top + area->bottom;
-  return region;
+  return retval;
 }
Index: gegl/operation/gegl-operation.c
===================================================================
--- gegl/operation/gegl-operation.c	(revision 1801)
+++ gegl/operation/gegl-operation.c	(working copy)
@@ -36,7 +36,7 @@ static void          attach             
 static GeglRectangle get_defined_region      (GeglOperation       *self);
 static GeglRectangle compute_affected_region (GeglOperation       *self,
                                               const gchar         *input_pad,
-                                              GeglRectangle        region);
+                                              const GeglRectangle *region);
 static GeglRectangle compute_input_request   (GeglOperation       *self,
                                               const gchar         *input_pad,
                                               const GeglRectangle *region);
@@ -133,20 +133,27 @@ gegl_operation_get_defined_region (GeglO
 }
 
 GeglRectangle
-gegl_operation_compute_affected_region (GeglOperation *self,
-                                        const gchar   *input_pad,
-                                        GeglRectangle  region)
+gegl_operation_compute_affected_region (GeglOperation       *self,
+                                        const gchar         *input_pad,
+                                        const GeglRectangle *region)
 {
-  GeglOperationClass *klass = GEGL_OPERATION_GET_CLASS (self);
+  GeglOperationClass *klass;
+  GeglRectangle       retval = { 0, };
 
-  if (region.width == 0 ||
-      region.height == 0)
-    return region;
+  g_return_val_if_fail (GEGL_IS_OPERATION (self), retval);
+  g_return_val_if_fail (input_pad != NULL, retval);
+  g_return_val_if_fail (region != NULL, retval);
+
+  klass = GEGL_OPERATION_GET_CLASS (self);
+
+  if (region->width == 0 ||
+      region->height == 0)
+    return *region;
 
   if (klass->compute_affected_region)
     return klass->compute_affected_region (self, input_pad, region);
 
-  return region;
+  return *region;
 }
 
 static GeglRectangle
@@ -363,9 +370,9 @@ get_defined_region (GeglOperation *self)
 }
 
 static GeglRectangle
-compute_affected_region (GeglOperation *self,
-                         const gchar   *input_pad,
-                         GeglRectangle  region)
+compute_affected_region (GeglOperation       *self,
+                         const gchar         *input_pad,
+                         const GeglRectangle *region)
 {
   if (self->node->is_graph)
     {
@@ -374,7 +381,8 @@ compute_affected_region (GeglOperation *
                input_pad,
                region);
     }
-  return region;
+
+  return *region;
 }
 
 void
Index: gegl/operation/gegl-operation.h
===================================================================
--- gegl/operation/gegl-operation.h	(revision 1801)
+++ gegl/operation/gegl-operation.h	(working copy)
@@ -87,9 +87,9 @@ struct _GeglOperationClass
    * graph. A default implementation of this, if not provided should probably
    * be to report that the entire defined region is dirtied.
    */
-  GeglRectangle   (*compute_affected_region)  (GeglOperation *operation,
-                                               const gchar   *input_pad,
-                                               GeglRectangle  region);
+  GeglRectangle   (*compute_affected_region)  (GeglOperation       *operation,
+                                               const gchar         *input_pad,
+                                               const GeglRectangle *region);
 
   /* computes the rectangle needed to be correctly computed in a buffer
    * on the named input_pad, for a given result rectangle
@@ -144,7 +144,7 @@ GeglNode      * gegl_operation_get_sourc
                                                      const gchar   *pad_name);
 GeglRectangle   gegl_operation_compute_affected_region (GeglOperation *operation,
                                                      const gchar   *input_pad,
-                                                     GeglRectangle  region);
+                                                     const GeglRectangle *region);
 GeglRectangle   gegl_operation_get_defined_region   (GeglOperation *operation);
 GeglRectangle   gegl_operation_adjust_result_region (GeglOperation *operation,
                                                      const GeglRectangle *roi);
Index: gegl/graph/gegl-node.c
===================================================================
--- gegl/graph/gegl-node.c	(revision 1801)
+++ gegl/graph/gegl-node.c	(working copy)
@@ -519,7 +519,8 @@ source_invalidated (GeglNode      *sourc
   if (destination->operation)
     {
       dirty_rect = gegl_operation_compute_affected_region (destination->operation,
-                                                       gegl_pad_get_name (destination_pad), *rect);
+                                                           gegl_pad_get_name (destination_pad),
+                                                           rect);
     }
   else
     {