/**
* A* pathfinding algorithm
*
* @param grid the grid to be used for pathfinding
* @param x target x coordinate in grid form
* @param y target y coordinate in grid form
* @return The next move to make for the ghost
*/
public Node pathFind(Grid grid, int x, int y) {
// Set target x, y
Node.tx = x;
Node.ty = y;
Node current = null, temp;
int block;
PriorityQueue<Node> opened = new PriorityQueue<Node>();
HashSet<Node> closed = new HashSet<Node>();
temp =
new Node(
this.x / Board.BLOCKSIZE, this.y / Board.BLOCKSIZE, 0); // current location of ghost
temp.init();
temp.setDir(dx, dy);
opened.offer(temp);
while (!opened.isEmpty()) {
current = opened.poll(); // get best node
closed.add(current); // add node to closed set (visited)
if (current.hCost == 0) // if future cost is 0, then it is target node
break;
block = grid.screenData[current.y][current.x];
// If can move, not abrupt, and unvisited, add to opened
if ((block & 1) == 0 && current.dir != 3) // Can move and not abrupt
{
temp = current.getChild(-1, 0); // get child node
if (!closed.contains(temp)) // Unvisited
opened.add(temp);
}
if ((block & 2) == 0 && current.dir != 4) {
temp = current.getChild(0, -1);
if (!closed.contains(temp)) opened.add(temp);
}
if ((block & 4) == 0 && current.dir != 1) {
temp = current.getChild(1, 0);
if (!closed.contains(temp)) opened.add(temp);
}
if ((block & 8) == 0 && current.dir != 2) {
temp = current.getChild(0, 1);
if (!closed.contains(temp)) opened.add(temp);
}
}
// if current.parent == null, then ghost is on pacman. Handle it by moving randomly
// current.parent.parent == null, then current is best next move
while (current.parent != null && current.parent.parent != null) current = current.parent;
return current;
}
