98 lines
2.8 KiB
C++
98 lines
2.8 KiB
C++
/* SPDX-FileCopyrightText: 2015 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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/** \file
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* \ingroup depsgraph
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*/
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#include "intern/builder/deg_builder_transitive.h"
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#include "MEM_guardedalloc.h"
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#include "intern/node/deg_node.hh"
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#include "intern/node/deg_node_component.hh"
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#include "intern/node/deg_node_operation.hh"
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#include "intern/debug/deg_debug.h"
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#include "intern/depsgraph.hh"
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#include "intern/depsgraph_relation.hh"
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namespace blender::deg {
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/* -------------------------------------------------- */
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/* Performs a transitive reduction to remove redundant relations.
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* https://en.wikipedia.org/wiki/Transitive_reduction
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*
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* XXX The current implementation is somewhat naive and has O(V*E) worst case
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* runtime.
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* A more optimized algorithm can be implemented later, e.g.
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*
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* http://www.sciencedirect.com/science/article/pii/0304397588900321/pdf?md5=3391e309b708b6f9cdedcd08f84f4afc&pid=1-s2.0-0304397588900321-main.pdf
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*
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* Care has to be taken to make sure the algorithm can handle the cyclic case
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* too! (unless we can to prevent this case early on).
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*/
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enum {
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OP_VISITED = 1,
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OP_REACHABLE = 2,
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};
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static void deg_graph_tag_paths_recursive(Node *node)
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{
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if (node->custom_flags & OP_VISITED) {
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return;
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}
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node->custom_flags |= OP_VISITED;
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for (Relation *rel : node->inlinks) {
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deg_graph_tag_paths_recursive(rel->from);
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/* Do this only in inlinks loop, so the target node does not get
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* flagged. */
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rel->from->custom_flags |= OP_REACHABLE;
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}
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}
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void deg_graph_transitive_reduction(Depsgraph *graph)
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{
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int num_removed_relations = 0;
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Vector<Relation *> relations_to_remove;
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for (OperationNode *target : graph->operations) {
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/* Clear tags. */
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for (OperationNode *node : graph->operations) {
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node->custom_flags = 0;
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}
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/* Mark nodes from which we can reach the target
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* start with children, so the target node and direct children are not
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* flagged. */
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target->custom_flags |= OP_VISITED;
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for (Relation *rel : target->inlinks) {
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deg_graph_tag_paths_recursive(rel->from);
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}
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/* Remove redundant paths to the target. */
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for (Relation *rel : target->inlinks) {
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if (rel->from->type == NodeType::TIMESOURCE) {
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/* HACK: time source nodes don't get "custom_flags" flag
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* set/cleared. */
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/* TODO: there will be other types in future, so iterators above
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* need modifying. */
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continue;
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}
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if (rel->from->custom_flags & OP_REACHABLE) {
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relations_to_remove.append(rel);
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}
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}
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for (Relation *rel : relations_to_remove) {
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rel->unlink();
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delete rel;
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}
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num_removed_relations += relations_to_remove.size();
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relations_to_remove.clear();
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}
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DEG_DEBUG_PRINTF((::Depsgraph *)graph, BUILD, "Removed %d relations\n", num_removed_relations);
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}
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} // namespace blender::deg
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