Java - Hover Over Image event

Question

I'm creating a menu for a game I'm currently designing and I'm using images I've designed in photoshop to use as buttons for the menus, but I'm wondering if there is any way to detect if the mouse is hovering over the image.

I've done this for regular rectangles previously but this shape is not a basic rectangle (Click HERE to view the shape).

The shape is being draw as a BufferedImage with Graphics2D.

Thank you in advance for the help!gya

Answer 1

You can map out your polygons and figure out which one was selected by adding a MouseListener. Next time you redraw, you can show the selection.

You can check if the event's point is contained within a polygon using:

[Java Docs] :: java.awt.Polygon.contains(Point)

Here is an example:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.util.*;
import java.util.List;
import javax.imageio.ImageIO;
import javax.swing.*;

public class PolygonDetectorPanel extends JPanel implements MouseListener {
    private static final long serialVersionUID = -8929816396666863908L;
    private BufferedImage backgroundImage;
    private List<Polygon> shapes;
    private Polygon selectedPoly;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame("Polygon Detector");
                PolygonDetectorPanel panel = new PolygonDetectorPanel();

                frame.setContentPane(panel);
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public PolygonDetectorPanel() {
        super();
        initialize();

        this.addMouseListener(this);
    }

    protected void initialize() {
        try {
            InputStream is = PolygonDetectorPanel.class.getClassLoader().getResourceAsStream("resources/buttons.png");
            this.backgroundImage = ImageIO.read(is);
        } catch (IOException e) {
            e.printStackTrace();
        }

        int width = this.backgroundImage.getWidth();
        int height = this.backgroundImage.getHeight();

        this.setPreferredSize(new Dimension(width, height));
        this.shapes = new ArrayList<Polygon>();

        int buttonStartX = 13;
        int buttonStartY = 54;
        int buttonOffset = 100;

        for (int i = 0; i < 4; i++) {
            int[] w  = { buttonStartX       , buttonStartY + 33 + (i * buttonOffset) };
            int[] nw = { buttonStartX +  50 , buttonStartY      + (i * buttonOffset) };
            int[] ne = { buttonStartX + 300 , buttonStartY      + (i * buttonOffset) };
            int[] e  = { buttonStartX + 350 , buttonStartY + 33 + (i * buttonOffset) };
            int[] se = { buttonStartX + 300 , buttonStartY + 66 + (i * buttonOffset) };
            int[] sw = { buttonStartX +  50 , buttonStartY + 66 + (i * buttonOffset) };

            int[] xPoints = { w[0], nw[0], ne[0], e[0], se[0], sw[0], w[0]};
            int[] yPoints = { w[1], nw[1], ne[1], e[1], se[1], sw[1], w[1]};

            this.shapes.add(new Polygon(xPoints, yPoints, 6));
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (this.backgroundImage != null) {
            g.drawImage(this.backgroundImage, 0, 0, null);
        }

        Graphics2D g2 = (Graphics2D) g;
        g2.setStroke(new BasicStroke(5, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND, 10.0f));

        for (Polygon poly : this.shapes) {
            if (poly == this.selectedPoly) {
                g.setColor(Color.GREEN);
            } else {
                g.setColor(Color.RED);
            }

            g.drawPolygon(poly);
        }
    }

    protected Polygon getClickedShape(Point point) {
        for (Polygon poly : this.shapes) {
            if (poly.contains(point)) {
                return poly;
            }
        }

        return null;
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        Polygon poly = getClickedShape(new Point(e.getX(), e.getY()));

        if (poly != null) {
            this.selectedPoly = poly;
        } else {
            this.selectedPoly = null;
        }

        repaint();
    }

    @Override
    public void mousePressed(MouseEvent e) { }

    @Override
    public void mouseReleased(MouseEvent e) { }

    @Override
    public void mouseEntered(MouseEvent e) { }

    @Override
    public void mouseExited(MouseEvent e) { }
}

Here is a screenshot.