Astar pathfinding in a grid
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package fr.uha.gasser.pathfinding.algorithm;
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import java.awt.*;
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import java.util.*;
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import java.util.List;
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class AStarSearch {
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private final Node start;
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private final Node goal;
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AStarSearch(Node start, Node goal) {
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this.start = start;
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this.goal = goal;
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}
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private Node search() {
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PriorityQueue<Node> frontier = new PriorityQueue<>();
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Set<Node> explored = new HashSet<>();
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frontier.add(start);
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while (!frontier.isEmpty()) {
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Node currentNode = frontier.poll();
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explored.add(currentNode);
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if (currentNode.getLoc().equals(goal.getLoc())) {
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return currentNode;
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}
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for (Node neighbor : getNeighbors(currentNode)) {
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// Ignore the neighbor which is already evaluated.
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if (explored.contains(neighbor)) continue;
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if (!frontier.contains(neighbor)) {
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neighbor.setParent(currentNode);
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neighbor.cost++;
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neighbor.hValue = neighbor.cost + neighbor.loc.distance(goal.loc);
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frontier.add(neighbor);
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}
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}
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}
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return null;
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}
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List<Node> shortestPath() {
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Node currentNode = search();
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LinkedList<Node> path = new LinkedList<>();
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while (currentNode.getParent() != null) {
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path.addFirst(currentNode);
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currentNode = currentNode.getParent();
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}
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return path;
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}
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private List<Node> getNeighbors(Node current) {
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LinkedList<Node> neighbors = new LinkedList<>();
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for (Direction direction : Direction.values()) {
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neighbors.add(getNeighbor(current, direction));
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}
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return neighbors;
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}
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private Node getNeighbor(Node current, Direction direction) {
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Node node = new Node(current);
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node.setLoc(new Point(current.loc.x + direction.x, current.loc.y + direction.y));
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return node;
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}
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private enum Direction {
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UP(0, 1),
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DOWN(0, -1),
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LEFT(-1, 0),
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LEFT_UP(-1, 1),
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LEFT_DOWN(-1, -1),
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RIGHT(1, 0),
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RIGHT_UP(1, 1),
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RIGHT_DOWN(1, -1);
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public final int x;
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public final int y;
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Direction(int x, int y) {
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this.x = x;
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this.y = y;
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}
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}
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}
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@@ -0,0 +1,35 @@
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package fr.uha.gasser.pathfinding.algorithm;
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import fr.uha.gasser.pathfinding.ui.Grid;
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import javax.swing.*;
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import java.awt.*;
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import java.util.List;
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public class AStarWorker extends SwingWorker<List<Node>, List<Node>> {
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private final Node start;
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private final Node goal;
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private final Grid target;
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private List<Node> path;
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public AStarWorker(Node start, Node goal, Grid target) {
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this.start = start;
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this.goal = goal;
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this.target = target;
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}
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@Override
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protected List<Node> doInBackground() throws Exception {
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AStarSearch aStar = new AStarSearch(start, goal);
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path = aStar.shortestPath();
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return path;
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}
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@Override
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protected void done() {
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if (this.isCancelled()) return;
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path.forEach(node -> {
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if (! node.loc.equals(goal.loc)) target.setTile(node.loc, Color.BLUE);
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});
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}
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}
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@@ -0,0 +1,46 @@
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package fr.uha.gasser.pathfinding.algorithm;
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import java.awt.*;
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public class Node implements Comparable<Node> {
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private Node parent;
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Point loc;
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int cost;
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double hValue; // heuristic value
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public Node(Point loc) {
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this.loc = loc;
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}
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Node(Node other) {
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this.parent = other.parent;
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this.loc = other.loc;
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this.cost = other.cost;
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this.hValue = other.hValue;
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}
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void setParent(Node parent) {
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this.parent = parent;
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}
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public void sethValue(double hValue) {
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this.hValue = hValue;
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}
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void setLoc(Point point) {
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this.loc = point;
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}
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public Point getLoc() {
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return loc;
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}
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Node getParent() {
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return parent;
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}
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@Override
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public int compareTo(Node other) {
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return Double.compare(this.hValue, other.hValue);
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}
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}
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@@ -0,0 +1,91 @@
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package fr.uha.gasser.pathfinding.ui;
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import fr.uha.gasser.pathfinding.algorithm.AStarWorker;
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import fr.uha.gasser.pathfinding.algorithm.Node;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import javax.swing.*;
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import java.awt.*;
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import java.awt.event.MouseAdapter;
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import java.awt.event.MouseEvent;
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public class App extends JFrame {
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private static final int ROWS = 30;
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private static final int COLS = 30;
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private static final int CELL_SIZE = 16;
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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private final Grid grid;
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private AStarWorker pathfinder;
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private Node startNode;
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private Node endNode;
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private JPanel gridPane;
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private App() throws HeadlessException {
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super("Pathfinding");
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grid = new Grid(ROWS, COLS, CELL_SIZE);
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setupInterface();
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pack();
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setVisible(true);
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}
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private void setupInterface() {
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gridPane = new JPanel();
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gridPane.setLayout(new GridLayout(ROWS, COLS));
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for (JLabel label : grid) {
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gridPane.add(label);
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}
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gridPane.addMouseListener(new MouseAdapter() {
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@Override
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public void mousePressed(MouseEvent e) {
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final JLabel at = (JLabel) gridPane.getComponentAt(e.getPoint());
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final Point loc = grid.findLoc(at);
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if (startNode == null) {
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grid.setTile(loc, Color.RED);
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startNode = new Node(loc);
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} else if (endNode == null) {
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grid.setTile(loc, Color.GREEN);
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endNode = new Node(loc);
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}
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}
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});
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final JMenuBar menuBar = new JMenuBar();
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final JMenuItem runItem = new JMenuItem("Run");
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menuBar.add(runItem);
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runItem.addActionListener(actionEvent -> doSearch());
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final JMenuItem cancelItem = new JMenuItem("Cancel");
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menuBar.add(cancelItem);
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cancelItem.addActionListener(actionEvent -> doCancel());
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final JMenuItem resetItem = new JMenuItem("Reset");
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menuBar.add(resetItem);
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resetItem.addActionListener(actionEvent -> doReset());
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setJMenuBar(menuBar);
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getContentPane().add(gridPane);
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}
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private void doReset() {
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pathfinder = null;
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startNode = null;
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endNode = null;
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grid.clear();
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}
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private void doCancel() {
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if (pathfinder == null) return;
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pathfinder.cancel(true);
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}
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private void doSearch() {
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pathfinder = new AStarWorker(startNode, endNode, grid);
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pathfinder.execute();
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}
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public static void main(String[] args) {
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EventQueue.invokeLater(App::new);
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}
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}
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package fr.uha.gasser.pathfinding.ui;
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import javax.swing.*;
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import javax.swing.border.Border;
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import java.awt.*;
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import java.awt.image.BufferedImage;
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import java.util.Iterator;
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public class Grid implements Iterable<JLabel> {
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private final static Border lineBorder = BorderFactory.createLineBorder(Color.BLACK, 1);
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private final JLabel[] cells;
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private final Dimension size;
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private int cellSize;
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Grid(int rows, int cols, int cellSize) {
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this.cellSize = cellSize;
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this.size = new Dimension(rows, cols);
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int size = rows * cols;
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this.cells = new JLabel[size];
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initGrid(size);
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}
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private void initGrid(int size) {
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for (int i = 0; i < size; i++) {
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final JLabel label = new JLabel();
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// Force cell size
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label.setPreferredSize(new Dimension(cellSize, cellSize));
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label.setMinimumSize(label.getPreferredSize());
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label.setMaximumSize(label.getPreferredSize());
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label.setBorder(lineBorder);
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label.setOpaque(true);
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cells[i] = label;
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}
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}
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public Point findLoc(JLabel cell) {
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for (int i = 0; i < cells.length; i++) {
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JLabel label = cells[i];
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if (cell == label) return new Point(i % size.width, i / size.height);
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}
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// Not found
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return new Point(-1, -1);
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}
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public void setTile(Point loc, Color color) {
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setTile(loc.x + size.width*loc.y, color);
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}
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private void setTile(int index, Color color) {
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final JLabel label = cells[index];
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label.setBackground(color);
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label.revalidate();
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}
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void clear() {
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for (JLabel cell : cells) {
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cell.setBackground(null);
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}
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}
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@Override
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public Iterator<JLabel> iterator() {
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return new Iterator<>() {
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private int pos = 0;
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@Override
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public boolean hasNext() {
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return cells.length > pos;
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}
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@Override
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public JLabel next() {
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return cells[pos++];
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}
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};
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}
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}
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