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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) 2014 Blender Foundation.
* All rights reserved.
*
* The Original Code is: all of this file.
*
* Contributor(s): Bastien Montagne
*
* ***** END GPL LICENSE BLOCK *****
*/
/** \file blender/blenlib/intern/astar.c
* \ingroup bli
* \brief An implementation of the A* (AStar) algorithm to solve shortest path problem.
*
* This library implements the simple A* (AStar) algorithm, an optimized version of
* classical dijkstra shortest path solver. The difference is that each future possible
* path is weighted from its 'shortest' (smallest) possible distance to destination,
* in addition to distance already walked. This heuristic allows more efficiency
* in finding optimal path.
*
* Implementation based on Wikipedia A* page [https://en.wikipedia.org/wiki/A*_search_algorithm].
*
* Note that most memory handling here is done through two different MemArena's. Those should also be used to allocate
* custom data needed to a specific use of A*.
* The first one, owned by BLI_AStarGraph, is for 'static' data that will live as long as the graph.
* The second one, owned by BLI_AStarSolution, is for data used during a single path solve. It will be cleared
* much more often than graph's one.
*/
#include <limits.h>
#include "MEM_guardedalloc.h"
#include "BLI_sys_types.h"
#include "BLI_compiler_attrs.h"
#include "BLI_alloca.h"
#include "BLI_heap.h"
#include "BLI_listbase.h"
#include "BLI_math.h"
#include "BLI_memarena.h"
#include "BLI_astar.h"
/**
* Init a node in A* graph.
*
* \param custom_data: an opaque pointer attached to this link, available e.g. to cost callback function.
*/
void BLI_astar_node_init(BLI_AStarGraph *as_graph, const int node_index, void *custom_data)
{
as_graph->nodes[node_index].custom_data = custom_data;
}
/**
* Add a link between two nodes of our A* graph.
*
* \param cost: the 'length' of the link (actual distance between two vertices or face centers e.g.).
* \param custom_data: an opaque pointer attached to this link, available e.g. to cost callback function.
*/
void BLI_astar_node_link_add(
BLI_AStarGraph *as_graph, const int node1_index, const int node2_index, const float cost, void *custom_data)
{
MemArena *mem = as_graph->mem;
BLI_AStarGNLink *link = BLI_memarena_alloc(mem, sizeof(*link));
LinkData *ld = BLI_memarena_alloc(mem, sizeof(*ld) * 2);
link->nodes[0] = node1_index;
link->nodes[1] = node2_index;
link->cost = cost;
link->custom_data = custom_data;
ld[0].data = ld[1].data = link;
BLI_addtail(&(as_graph->nodes[node1_index].neighbor_links), &ld[0]);
BLI_addtail(&(as_graph->nodes[node2_index].neighbor_links), &ld[1]);
}
/**
* \return The index of the other node of given link.
*/
int BLI_astar_node_link_other_node(BLI_AStarGNLink *lnk, const int idx)
{
return (lnk->nodes[0] == idx) ? lnk->nodes[1] : lnk->nodes[0];
}
/**
* Initialize a solution data for given A* graph. Does not compute anything!
*
* \param custom_data: an opaque pointer attached to this link, available e.g. to cost callback function.
*
* \note BLI_AStarSolution stores nearly all data needed during solution compute.
*/
void BLI_astar_solution_init(BLI_AStarGraph *as_graph, BLI_AStarSolution *as_solution, void *custom_data)
{
MemArena *mem = as_solution->mem;
size_t node_num = (size_t)as_graph->node_num;
if (mem == NULL) {
mem = BLI_memarena_new(BLI_MEMARENA_STD_BUFSIZE, __func__);
as_solution->mem = mem;
}
/* else memarena should be cleared */
as_solution->steps = 0;
as_solution->prev_nodes = BLI_memarena_alloc(mem, sizeof(*as_solution->prev_nodes) * node_num);
as_solution->prev_links = BLI_memarena_alloc(mem, sizeof(*as_solution->prev_links) * node_num);
as_solution->custom_data = custom_data;
as_solution->done_nodes = BLI_BITMAP_NEW_MEMARENA(mem, node_num);
as_solution->g_costs = BLI_memarena_alloc(mem, sizeof(*as_solution->g_costs) * node_num);
as_solution->g_steps = BLI_memarena_alloc(mem, sizeof(*as_solution->g_steps) * node_num);
}
/**
* Clear given solution's data, but does not release its memory. Avoids having to recreate/allocate
* a memarena in loops, e.g.
*
* \note This *has to be called* between each path solving.
*/
void BLI_astar_solution_clear(BLI_AStarSolution *as_solution)
{
if (as_solution->mem) {
BLI_memarena_clear(as_solution->mem);
}
as_solution->steps = 0;
as_solution->prev_nodes = NULL;
as_solution->prev_links = NULL;
as_solution->custom_data = NULL;
as_solution->done_nodes = NULL;
as_solution->g_costs = NULL;
as_solution->g_steps = NULL;
}
/**
* Release the memory allocated for this solution.
*/
void BLI_astar_solution_free(BLI_AStarSolution *as_solution)
{
if (as_solution->mem) {
BLI_memarena_free(as_solution->mem);
as_solution->mem = NULL;
}
}
/**
* Init an A* graph. Total number of nodes must be known.
*
* Nodes might be e.g. vertices, faces, ...
*
* \param custom_data: an opaque pointer attached to this link, available e.g. to cost callback function.
*/
void BLI_astar_graph_init(BLI_AStarGraph *as_graph, const int node_num, void *custom_data)
{
MemArena *mem = as_graph->mem;
if (mem == NULL) {
mem = BLI_memarena_new(BLI_MEMARENA_STD_BUFSIZE, __func__);
as_graph->mem = mem;
}
/* else memarena should be cleared */
as_graph->node_num = node_num;
as_graph->nodes = BLI_memarena_calloc(mem, sizeof(*as_graph->nodes) * (size_t)node_num);
as_graph->custom_data = custom_data;
}
void BLI_astar_graph_free(BLI_AStarGraph *as_graph)
{
if (as_graph->mem) {
BLI_memarena_free(as_graph->mem);
as_graph->mem = NULL;
}
}
/**
* Solve a path in given graph, using given 'cost' callback function.
*
* \param max_steps: maximum number of nodes the found path may have. Useful in performance-critical usages.
* If no path is found within given steps, returns false too.
* \return true if a path was found, false otherwise.
*/
bool BLI_astar_graph_solve(
BLI_AStarGraph *as_graph, const int node_index_src, const int node_index_dst, astar_f_cost f_cost_cb,
BLI_AStarSolution *r_solution, const int max_steps)
{
Heap *todo_nodes;
BLI_bitmap *done_nodes = r_solution->done_nodes;
int *prev_nodes = r_solution->prev_nodes;
BLI_AStarGNLink **prev_links = r_solution->prev_links;
float *g_costs = r_solution->g_costs;
int *g_steps = r_solution->g_steps;
r_solution->steps = 0;
prev_nodes[node_index_src] = -1;
BLI_BITMAP_SET_ALL(done_nodes, false, as_graph->node_num);
copy_vn_fl(g_costs, as_graph->node_num, FLT_MAX);
g_costs[node_index_src] = 0.0f;
g_steps[node_index_src] = 0;
if (node_index_src == node_index_dst) {
return true;
}
todo_nodes = BLI_heap_new();
BLI_heap_insert(todo_nodes,
f_cost_cb(as_graph, r_solution, NULL, -1, node_index_src, node_index_dst),
POINTER_FROM_INT(node_index_src));
while (!BLI_heap_is_empty(todo_nodes)) {
const int node_curr_idx = POINTER_AS_INT(BLI_heap_pop_min(todo_nodes));
BLI_AStarGNode *node_curr = &as_graph->nodes[node_curr_idx];
LinkData *ld;
if (BLI_BITMAP_TEST(done_nodes, node_curr_idx)) {
/* Might happen, because we always add nodes to heap when evaluating them,
* without ever removing them. */
continue;
}
/* If we are limited in amount of steps to find a path, skip if we reached limit. */
if (max_steps && g_steps[node_curr_idx] > max_steps) {
continue;
}
if (node_curr_idx == node_index_dst) {
/* Success! Path found... */
r_solution->steps = g_steps[node_curr_idx] + 1;
BLI_heap_free(todo_nodes, NULL);
return true;
}
BLI_BITMAP_ENABLE(done_nodes, node_curr_idx);
for (ld = node_curr->neighbor_links.first; ld; ld = ld->next) {
BLI_AStarGNLink *link = ld->data;
const int node_next_idx = BLI_astar_node_link_other_node(link, node_curr_idx);
if (!BLI_BITMAP_TEST(done_nodes, node_next_idx)) {
float g_cst = g_costs[node_curr_idx] + link->cost;
if (g_cst < g_costs[node_next_idx]) {
prev_nodes[node_next_idx] = node_curr_idx;
prev_links[node_next_idx] = link;
g_costs[node_next_idx] = g_cst;
g_steps[node_next_idx] = g_steps[node_curr_idx] + 1;
/* We might have this node already in heap, but since this 'instance' will be evaluated first,
* no problem. */
BLI_heap_insert(todo_nodes,
f_cost_cb(as_graph, r_solution, link, node_curr_idx, node_next_idx, node_index_dst),
POINTER_FROM_INT(node_next_idx));
}
}
}
}
BLI_heap_free(todo_nodes, NULL);
return false;
}
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