NAME
AI::Pathfinding::AStar - Perl implementation of the A* pathfinding
algorithm
SYNOPSIS
package My::Map::Package;
use base AI::Pathfinding::AStar;
# Methods required by AI::Pathfinding::AStar
sub getSurrounding { ... }
package main;
use My::Map::Package;
my $map = My::Map::Package->new or die "No map for you!";
my $path = $map->findPath($start, $target);
print join(', ', @$path), "\n";
#Or you can do it incrementally, say 3 nodes at a time
my $state = $map->findPathIncr($start, $target, undef, 3);
while ($state->{path}->[-1] ne $target) {
print join(', ', @{$state->{path}}), "\n";
$state = $map->findPathIncr($start, $target, $state, 3);
}
print "Completed Path: ", join(', ', @{$state->{path}}), "\n";
DESCRIPTION
This module implements the A* pathfinding algorithm. It acts as a base
class from which a custom map object can be derived. It requires from
the map object a subroutine named "getSurrounding" (described below) and
provides to the object two routines called "findPath" and "findPathIncr"
(also described below.) It should also be noted that
AI::Pathfinding::AStar defines two other subs ("calcF" and "calcG")
which are used only by the "findPath" routines.
AI::Pathfinding::AStar requires that the map object define a routine
named "getSurrounding" which accepts the starting and target node ids
for which you are calculating the path. In return it should provide an
array reference containing the following details about each of the
immediately surrounding nodes:
* Node ID
* Cost to enter that node
* Heuristic
Basically you should return an array reference like this: "[ [$node1,
$cost1, $h1], [$node2, $cost2, $h2], [...], ...];" For more information
on heuristics and the best ways to calculate them, visit the links
listed in the *SEE ALSO* section below. For a very brief idea of how to
write a getSurrounding routine, refer to the included tests.
As mentioned earlier, AI::Pathfinding::AStar provides two routines named
"findPath" and "findPathIncr". "findPath" requires as input the starting
and target node identifiers. It is unimportant what format you choose
for your node IDs. As long as they are unique, and can be distinguished
by Perl's "exists $hash{$nodeid}", then they will work. "findPath" then
returns an array (or reference) of node identifiers representing the
least expensive path to your target node. An empty array means that the
target node is entirely unreacheable from the given source.
"findPathIncr" on the other hand allows you to calculate a particularly
long path in chunks. "findPathIncr" also takes the starting and target
node identifiers but also accepts a "state" variable and a maxiumum
number of nodes to calculate before returning. "findPathIncr" then
returns a hash representing the current state that can then be passed
back in for further processing later. The current path can be found in
"$state-"{path}>.
PREREQUISITES
This module requires Heap (specifically Heap::Fibonacci and Heap::Elem)
to function.
SEE ALSO
<
http://www.policyalmanac.org/games/aStarTutorial.htm>,
<
http://xenon.stanford.edu/~amitp/gameprog.html>
AUTHOR
Aaron Dalton -
[email protected] This is my very first CPAN contribution
and I am not a professional programmer. Any feedback you may have, even
regarding issues of style, would be greatly appreciated. I hope it is of
some use.
COPYRIGHT AND LICENSE
Copyright (c) 2004 Aaron Dalton. All rights reserved. This library is
free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
