static gboolean gegl_operation_point_filter_op_process
                              (GeglOperation       *operation,
                               GeglOperationContext *context,
                               const gchar          *output_pad,
                               const GeglRectangle  *roi)
{
  GeglBuffer               *input;
  GeglBuffer               *output;
  gboolean                  success = FALSE;

  input = gegl_operation_context_get_source (context, "input");

  if (gegl_can_do_inplace_processing (operation, input, roi))
    {
      output = g_object_ref (input);
      gegl_operation_context_take_object (context, "output", G_OBJECT (output));
    }
  else
    {
      output = gegl_operation_context_get_target (context, "output");
    }

  success = gegl_operation_point_filter_process (operation, input, output, roi);
  if (output == GEGL_BUFFER (operation->node->cache))
    gegl_cache_computed (operation->node->cache, roi);

  if (input != NULL)
    g_object_unref (input);
  return success;
}
static gboolean
gegl_operation_source_process (GeglOperation        *operation,
                               GeglOperationContext *context,
                               const gchar          *output_prop,
                               const GeglRectangle  *result,
                               gint                  level)
{
  GeglOperationSourceClass *klass = GEGL_OPERATION_SOURCE_GET_CLASS (operation);
  GeglBuffer               *output;
  gboolean                  success;

  if (strcmp (output_prop, "output"))
    {
      g_warning ("requested processing of %s pad on a source operation", output_prop);
      return FALSE;
    }

  g_assert (klass->process);
  output = gegl_operation_context_get_target (context, "output");
  success = klass->process (operation, output, result, level);

  if (output == GEGL_BUFFER (operation->node->cache))
    gegl_cache_computed (operation->node->cache, result);

  return success;
}
static gboolean
gegl_operation_filter_process (GeglOperation        *operation,
                               GeglOperationContext *context,
                               const gchar          *output_prop,
                               const GeglRectangle  *result,
                               gint                  level)
{
  GeglOperationFilterClass *klass;
  GeglBuffer               *input;
  GeglBuffer               *output;
  gboolean                  success = FALSE;

  klass = GEGL_OPERATION_FILTER_GET_CLASS (operation);

  g_assert (klass->process);

  if (strcmp (output_prop, "output"))
    {
      g_warning ("requested processing of %s pad on a filter", output_prop);
      return FALSE;
    }

  input  = gegl_operation_context_get_source (context, "input");
  output = gegl_operation_context_get_target (context, "output");

  success = klass->process (operation, input, output, result, level);

  if (output == GEGL_BUFFER (operation->node->cache))
    gegl_cache_computed (operation->node->cache, result);

  if (input != NULL)
    g_object_unref (input);
  return success;
}
/* we replicate the process function from GeglOperationComposer to be
 * able to bail out earlier for some common processing time pitfalls
 */
static gboolean
gegl_operation_composer_process2 (GeglOperation        *operation,
                                  GeglOperationContext *context,
                                  const gchar          *output_prop,
                                  const GeglRectangle  *result)
{
  GeglOperationComposerClass *klass   = GEGL_OPERATION_COMPOSER_GET_CLASS (operation);
  GeglBuffer                 *input;
  GeglBuffer                 *aux;
  GeglBuffer                 *output;
  gboolean                    success = FALSE;

  if (strcmp (output_prop, "output"))
    {
      g_warning ("requested processing of %s pad on a composer", output_prop);
      return FALSE;
    }

  input = gegl_operation_context_get_source (context, "input");
  aux   = gegl_operation_context_get_source (context, "aux");

  if (gegl_can_do_inplace_processing (operation, input, result))
    {
      output = g_object_ref (input);
      gegl_operation_context_take_object (context, "output", G_OBJECT (output));
    }
  else
    output = gegl_operation_context_get_target (context, "output");
    
    {
      gboolean done = FALSE;

      if (result->width == 0 ||
          result->height == 0)
        done = TRUE;

      success = done;
      if (!done)
        {
          success = klass->process (operation, input, aux, output, result);

          if (output == GEGL_BUFFER (operation->node->cache))
            gegl_cache_computed (operation->node->cache, result);
        }
      if (input)
         g_object_unref (input);
      if (aux)
         g_object_unref (aux);
    }

  return success;
}
static gboolean
gegl_operation_composer_process (GeglOperation        *operation,
                                 GeglOperationContext *context,
                                 const gchar          *output_prop,
                                 const GeglRectangle  *result,
                                 gint                  level)
{
  GeglOperationComposerClass *klass   = GEGL_OPERATION_COMPOSER_GET_CLASS (operation);
  GeglBuffer                 *input;
  GeglBuffer                 *aux;
  GeglBuffer                 *output;
  gboolean                    success = FALSE;

  if (strcmp (output_prop, "output"))
    {
      g_warning ("requested processing of %s pad on a composer", output_prop);
      return FALSE;
    }

  input = gegl_operation_context_get_source (context, "input");
  aux   = gegl_operation_context_get_source (context, "aux");
  output = gegl_operation_context_get_target (context, "output");

  /* A composer with a NULL aux, can still be valid, the
   * subclass has to handle it.
   */
  if (input != NULL ||
      aux != NULL)
    {
      success = klass->process (operation, input, aux, output, result, level);

      if (output == GEGL_BUFFER (operation->node->cache))
        gegl_cache_computed (operation->node->cache, result);

      if (input)
        g_object_unref (input);
      if (aux)
        g_object_unref (aux);
    }
  else
    {
      g_warning ("%s received NULL input and aux",
                 gegl_node_get_debug_name (operation->node));
    }

  return success;
}
/**
 * gegl_graph_process:
 * @path: The traversal path
 *
 * Process the prepared request. This will return the
 * resulting buffer from the final node, or NULL if
 * that node is a sink.
 *
 * If gegl_graph_prepare_request has not been called
 * the behavior of this function is undefined.
 *
 * Return value: (transfer full): The result of the graph, or NULL if
 * there is no output pad.
 */
GeglBuffer *
gegl_graph_process (GeglGraphTraversal *path,
                    gint                level)
{
  GList *list_iter = NULL;
  GeglBuffer *result = NULL;
  GeglOperationContext *context = NULL;
  GeglOperationContext *last_context = NULL;
  GeglBuffer *operation_result = NULL;

  for (list_iter = path->dfs_path; list_iter; list_iter = list_iter->next)
    {
      GeglNode *node = GEGL_NODE (list_iter->data);
      GeglOperation *operation = node->operation;
      g_return_val_if_fail (node, NULL);
      g_return_val_if_fail (operation, NULL);
      
      GEGL_INSTRUMENT_START();

      operation_result = NULL;

      if (last_context)
        gegl_operation_context_purge (last_context);
      
      context = g_hash_table_lookup (path->contexts, node);
      g_return_val_if_fail (context, NULL);

      GEGL_NOTE (GEGL_DEBUG_PROCESS,
                 "Will process %s result_rect = %d, %d %d×%d",
                 gegl_node_get_debug_name (node),
                 context->result_rect.x, context->result_rect.y, context->result_rect.width, context->result_rect.height);
      
      if (context->need_rect.width > 0 && context->need_rect.height > 0)
        {
          if (context->cached)
            {
              GEGL_NOTE (GEGL_DEBUG_PROCESS,
                         "Using cached result for %s",
                         gegl_node_get_debug_name (node));
              operation_result = GEGL_BUFFER (node->cache);
            }
          else
            {
              /* provide something on input pad, always - this makes having
                 behavior depending on it not being set.. not work, is
                 sacrifising that worth it?
               */
              if (gegl_node_has_pad (node, "input") &&
                  !gegl_operation_context_get_object (context, "input"))
                {
                  gegl_operation_context_set_object (context, "input", G_OBJECT (gegl_graph_get_shared_empty(path)));
                }

              context->level = level;

              /* note: this hard-coding of "output" makes some more custom
               * graph topologies harder than neccesary.
               */
              gegl_operation_process (operation, context, "output", &context->need_rect, context->level);
              operation_result = GEGL_BUFFER (gegl_operation_context_get_object (context, "output"));

              if (operation_result && operation_result == (GeglBuffer *)operation->node->cache)
                gegl_cache_computed (operation->node->cache, &context->need_rect, level);
            }
        }
      else
        {
          operation_result = NULL;
        }

      if (operation_result)
        {
          GeglPad *output_pad = gegl_node_get_pad (node, "output");
          GList   *targets = gegl_graph_get_connected_output_contexts (path, output_pad);
          GList   *targets_iter;

          GEGL_NOTE (GEGL_DEBUG_PROCESS,
                     "Will deliver the results of %s:%s to %d targets",
                     gegl_node_get_debug_name (node),
                     "output",
                     g_list_length (targets));

          if (g_list_length (targets) > 1)
            gegl_object_set_has_forked (G_OBJECT (operation_result));

          for (targets_iter = targets; targets_iter; targets_iter = g_list_next (targets_iter))
            {
              ContextConnection *target_con = targets_iter->data;
              gegl_operation_context_set_object (target_con->context, target_con->name, G_OBJECT (operation_result));
            }
          g_list_free_full (targets, free_context_connection);
        }
      last_context = context;

      GEGL_INSTRUMENT_END ("process", gegl_node_get_operation (node));
    }
  if (last_context)
    {
      if (operation_result)
        result = g_object_ref (operation_result);
      else if (gegl_node_has_pad (last_context->operation->node, "output"))
        result = g_object_ref (gegl_graph_get_shared_empty (path));
      gegl_operation_context_purge (last_context);
    }

  return result;
}