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/*
* ***** BEGIN GPL LICENSE BLOCK *****
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* The Original Code is Copyright (C) 2015 Blender Foundation.
* All rights reserved.
*
* Contributor(s): Lukas Toenne,
* Sergey Sharybin,
*
* ***** END GPL LICENSE BLOCK *****
*/
/** \file blender/depsgraph/intern/builder/deg_builder_transitive.cc
* \ingroup depsgraph
*/
#include "intern/builder/deg_builder_transitive.h"
#include "MEM_guardedalloc.h"
#include "intern/nodes/deg_node.h"
#include "intern/nodes/deg_node_component.h"
#include "intern/nodes/deg_node_operation.h"
#include "intern/depsgraph.h"
#include "util/deg_util_foreach.h"
namespace DEG {
/* -------------------------------------------------- */
/* Performs a transitive reduction to remove redundant relations.
* https://en.wikipedia.org/wiki/Transitive_reduction
*
* XXX The current implementation is somewhat naive and has O(V*E) worst case
* runtime.
* A more optimized algorithm can be implemented later, e.g.
*
* http://www.sciencedirect.com/science/article/pii/0304397588900321/pdf?md5=3391e309b708b6f9cdedcd08f84f4afc&pid=1-s2.0-0304397588900321-main.pdf
*
* Care has to be taken to make sure the algorithm can handle the cyclic case
* too! (unless we can to prevent this case early on).
*/
enum {
OP_VISITED = 1,
OP_REACHABLE = 2,
};
static void deg_graph_tag_paths_recursive(DepsNode *node)
{
if (node->done & OP_VISITED) {
return;
}
node->done |= OP_VISITED;
foreach (DepsRelation *rel, node->inlinks) {
deg_graph_tag_paths_recursive(rel->from);
/* Do this only in inlinks loop, so the target node does not get
* flagged.
*/
rel->from->done |= OP_REACHABLE;
}
}
void deg_graph_transitive_reduction(Depsgraph *graph)
{
foreach (OperationDepsNode *target, graph->operations) {
/* Clear tags. */
foreach (OperationDepsNode *node, graph->operations) {
node->done = 0;
}
/* mark nodes from which we can reach the target
* start with children, so the target node and direct children are not
* flagged.
*/
target->done |= OP_VISITED;
foreach (DepsRelation *rel, target->inlinks) {
deg_graph_tag_paths_recursive(rel->from);
}
/* Remove redundant paths to the target. */
for (DepsNode::Relations::const_iterator it_rel = target->inlinks.begin();
it_rel != target->inlinks.end();
)
{
DepsRelation *rel = *it_rel;
/* Increment in advance, so we can safely remove the relation. */
++it_rel;
if (rel->from->type == DEG_NODE_TYPE_TIMESOURCE) {
/* HACK: time source nodes don't get "done" flag set/cleared. */
/* TODO: there will be other types in future, so iterators above
* need modifying.
*/
}
else if (rel->from->done & OP_REACHABLE) {
OBJECT_GUARDED_DELETE(rel, DepsRelation);
}
}
}
}
} // namespace DEG
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