package stray.pathfinding;
import stray.blocks.Block;
import stray.pathfinding.heuristics.ClosestHeuristic;
import stray.world.World;
import com.badlogic.gdx.utils.Array;
/**
* A path finder implementation that uses the AStar heuristic based algorithm to
* determine a path.
*
* @author Kevin Glass
*/
public class AStarPathFinder implements PathFinder {
/** The set of nodes that have been searched through */
private Array closed = new Array();
/** The set of nodes that we do not yet consider fully searched */
private SortedList open = new SortedList();
/** The map being searched */
private TileBasedMap map;
/** The maximum depth of search we're willing to accept before giving up */
private int maxSearchDistance;
/** The complete set of nodes across the map */
private Node[][] nodes;
/** True if we allow diaganol movement */
private boolean allowDiagMovement;
/** The heuristic we're applying to determine which nodes to search first */
private AStarHeuristic heuristic;
/**
* Create a path finder with the default heuristic - closest to target.
*
* @param map
* The map to be searched
* @param maxSearchDistance
* The maximum depth we'll search before giving up
* @param allowDiagMovement
* True if the search should try diaganol movement
*/
public AStarPathFinder(TileBasedMap map, int maxSearchDistance, boolean allowDiagMovement) {
this(map, maxSearchDistance, allowDiagMovement, new ClosestHeuristic());
}
/**
* Create a path finder
*
* @param heuristic
* The heuristic used to determine the search order of the map
* @param map
* The map to be searched
* @param maxSearchDistance
* The maximum depth we'll search before giving up
* @param allowDiagMovement
* True if the search should try diaganol movement
*/
public AStarPathFinder(TileBasedMap map, int maxSearchDistance, boolean allowDiagMovement,
AStarHeuristic heuristic) {
this.heuristic = heuristic;
this.map = map;
this.maxSearchDistance = maxSearchDistance;
this.allowDiagMovement = allowDiagMovement;
nodes = new Node[map.getWidthInTiles()][map.getHeightInTiles()];
for (int x = 0; x < map.getWidthInTiles(); x++) {
for (int y = 0; y < map.getHeightInTiles(); y++) {
nodes[x][y] = new Node(x, y);
}
}
}
public Block getRoom(int x, int y) {
if (map instanceof World) {
return ((World) map).getBlock(x, y);
}
return null;
}
/**
* @see PathFinder#findPath(Mover, int, int, int, int)
*/
public Path findPath(Mover mover, int sx, int sy, int tx, int ty) {
// easy first check, if the destination is blocked, we can't get there
long time = System.currentTimeMillis();
if (map.blocked(mover, tx, ty)) {
return null;
}
// initial state for A*. The closed group is empty. Only the starting
// tile is in the open list and it'e're already there
nodes[sx][sy].cost = 0;
nodes[sx][sy].depth = 0;
closed.clear();
open.clear();
open.add(nodes[sx][sy]);
nodes[tx][ty].parent = null;
// while we haven't exceeded our max search depth
int maxDepth = 0;
while ((maxDepth < maxSearchDistance) && (open.size() != 0)) {
if (System.currentTimeMillis() - time > 150l) return null;
// pull out the first node in our open list, this is determined to
// be the most likely to be the next step based on our heuristic
Node current = getFirstInOpen();
if (current == nodes[tx][ty]) {
break;
}
removeFromOpen(current);
addToClosed(current);
// search through all the neighbours of the current node evaluating
// them as next steps
for (int x = -1; x < 2; x++) {
for (int y = -1; y < 2; y++) {
// not a neighbour, its the current tile
if ((x == 0) && (y == 0)) {
continue;
}
// if we're not allowing diaganol movement then only
// one of x or y can be set
if (!allowDiagMovement) {
if ((x != 0) && (y != 0)) {
continue;
}
}
// determine the location of the neighbour and evaluate it
int xp = x + current.x;
int yp = y + current.y;
// System.out.println("pf: " + isValidLocation(mover,
// current.x, current.y, sx, sy, xp, yp));
if (isValidLocation(mover, current.x, current.y, sx, sy, xp, yp)) {
// the cost to get to this node is cost the current plus
// the movement
// cost to reach this node. Note that the heursitic
// value is only used
// in the sorted open list
float nextStepCost = current.cost
+ getMovementCost(mover, current.x, current.y, xp, yp);
Node neighbour = nodes[xp][yp];
map.pathFinderVisited(xp, yp);
// if the new cost we've determined for this node is
// lower than
// it has been previously makes sure the node hasn'e've
// determined that there might have been a better path
// to get to
// this node so it needs to be re-evaluated
if (nextStepCost < neighbour.cost) {
if (inOpenList(neighbour)) {
removeFromOpen(neighbour);
}
if (inClosedList(neighbour)) {
removeFromClosed(neighbour);
}
}
// if the node hasn't already been processed and
// discarded then
// reset it's cost to our current cost and add it as a
// next possible
// step (i.e. to the open list)
if (!inOpenList(neighbour) && !(inClosedList(neighbour))) {
neighbour.cost = nextStepCost;
neighbour.heuristic = getHeuristicCost(mover, xp, yp, tx, ty);
maxDepth = Math.max(maxDepth, neighbour.setParent(current));
addToOpen(neighbour);
}
}
}
}
}
// since we'e've run out of search
// there was no path. Just return null
if (nodes[tx][ty].parent == null) {
return null;
}
// At this point we've definitely found a path so we can uses the parent
// references of the nodes to find out way from the target location back
// to the start recording the nodes on the way.
Path path = new Path();
Node target = nodes[tx][ty];
while (target != nodes[sx][sy]) {
path.prependStep(target.x, target.y);
target = target.parent;
}
path.prependStep(sx, sy);
// thats it, we have our path
return path;
}
/**
* Get the first element from the open list. This is the next one to be
* searched.
*
* @return The first element in the open list
*/
protected Node getFirstInOpen() {
return (Node) open.first();
}
/**
* Add a node to the open list
*
* @param node
* The node to be added to the open list
*/
protected void addToOpen(Node node) {
open.add(node);
}
/**
* Check if a node is in the open list
*
* @param node
* The node to check for
* @return True if the node given is in the open list
*/
protected boolean inOpenList(Node node) {
return open.contains(node);
}
/**
* Remove a node from the open list
*
* @param node
* The node to remove from the open list
*/
protected void removeFromOpen(Node node) {
open.remove(node);
}
/**
* Add a node to the closed list
*
* @param node
* The node to add to the closed list
*/
protected void addToClosed(Node node) {
closed.add(node);
}
/**
* Check if the node supplied is in the closed list
*
* @param node
* The node to search for
* @return True if the node specified is in the closed list
*/
protected boolean inClosedList(Node node) {
return closed.contains(node, true);
}
/**
* Remove a node from the closed list
*
* @param node
* The node to remove from the closed list
*/
protected void removeFromClosed(Node node) {
closed.removeValue(node, true);
}
/**
* Check if a given location is valid for the supplied mover
*
* @param mover
* The mover that would hold a given location
* @param sx
* The starting x coordinate
* @param sy
* The starting y coordinate
* @param x
* The x coordinate of the location to check
* @param y
* The y coordinate of the location to check
* @return True if the location is valid for the given mover
*/
protected boolean isValidLocation(Mover mover, int cx, int cy, int sx, int sy, int x, int y) {
boolean invalid = (x < 0) || (y < 0) || (x >= map.getWidthInTiles())
|| (y >= map.getHeightInTiles());
if ((!invalid) && ((sx != x) || (sy != y))) {
invalid = map.blocked(mover, x, y);
}
if (!map.canMoveDirectly(mover, cx, cy, x, y)) return false;
return !invalid;
}
/**
* Get the cost to move through a given location
*
* @param mover
* The entity that is being moved
* @param sx
* The x coordinate of the tile whose cost is being determined
* @param sy
* The y coordiante of the tile whose cost is being determined
* @param tx
* The x coordinate of the target location
* @param ty
* The y coordinate of the target location
* @return The cost of movement through the given tile
*/
public float getMovementCost(Mover mover, int sx, int sy, int tx, int ty) {
return map.getCost(mover, sx, sy, tx, ty);
}
/**
* Get the heuristic cost for the given location. This determines in which
* order the locations are processed.
*
* @param mover
* The entity that is being moved
* @param x
* The x coordinate of the tile whose cost is being determined
* @param y
* The y coordiante of the tile whose cost is being determined
* @param tx
* The x coordinate of the target location
* @param ty
* The y coordinate of the target location
* @return The heuristic cost assigned to the tile
*/
public float getHeuristicCost(Mover mover, int x, int y, int tx, int ty) {
return heuristic.getCost(map, mover, x, y, tx, ty);
}
/**
* A simple sorted list
*
* @author kevin
*/
private class SortedList {
/** The list of elements */
private Array list = new Array();
/**
* Retrieve the first element from the list
*
* @return The first element from the list
*/
public Object first() {
return list.get(0);
}
/**
* Empty the list
*/
public void clear() {
list.clear();
}
/**
* Add an element to the list - causes sorting
*
* @param o
* The element to add
*/
public void add(Object o) {
list.add(o);
list.sort();
}
/**
* Remove an element from the list
*
* @param o
* The element to remove
*/
public void remove(Object o) {
list.removeValue(o, true);
}
/**
* Get the number of elements in the list
*
* @return The number of element in the list
*/
public int size() {
return list.size;
}
/**
* Check if an element is in the list
*
* @param o
* The element to search for
* @return True if the element is in the list
*/
public boolean contains(Object o) {
return list.contains(o, true);
}
}
/**
* A single node in the search graph
*/
private class Node implements Comparable {
/** The x coordinate of the node */
private int x;
/** The y coordinate of the node */
private int y;
/** The path cost for this node */
private float cost;
/** The parent of this node, how we reached it in the search */
private Node parent;
/** The heuristic cost of this node */
private float heuristic;
/** The search depth of this node */
private int depth;
/**
* Create a new node
*
* @param x
* The x coordinate of the node
* @param y
* The y coordinate of the node
*/
public Node(int x, int y) {
this.x = x;
this.y = y;
}
/**
* Set the parent of this node
*
* @param parent
* The parent node which lead us to this node
* @return The depth we have no reached in searching
*/
public int setParent(Node parent) {
depth = parent.depth + 1;
this.parent = parent;
return depth;
}
/**
* @see Comparable#compareTo(Object)
*/
public int compareTo(Object other) {
Node o = (Node) other;
float f = heuristic + cost;
float of = o.heuristic + o.cost;
if (f < of) {
return -1;
} else if (f > of) {
return 1;
} else {
return 0;
}
}
}
}