Java Swing game has poor performance when many sprites are on screen

Question

I'm making a simple tower defense game in Swing and I've run into a performance problem when I try to put many sprites (more than 20) on screen.

The whole game takes place on a JPanel which has setIgnoreRepaint(true). Here is the paintComponent method (con is the Controller):

public void paintComponent(Graphics g){
    super.paintComponent(g);
    //Draw grid
    g.drawImage(background, 0, 0, null);
    if (con != null){
        //Draw towers
        for (Tower t : con.getTowerList()){
            t.paintTower(g);
        }
        //Draw targets
        if (con.getTargets().size() != 0){
            for (Target t : con.getTargets()){
                t.paintTarget(g);
            }
            //Draw shots
            for (Shot s : con.getShots()){
                s.paintShot(g);
            }
        }
    }
}

The Target class simple paints a BufferedImage at its current location. The getImage method doesn't create a new BufferedImage, it simply returns the Controller class's instance of it:

public void paintTarget(Graphics g){
    g.drawImage(con.getImage("target"), getPosition().x - 20, getPosition().y - 20, null);
}

Each target runs a Swing Timer to calculate its position. This is the ActionListener it calls:

public void actionPerformed(ActionEvent e) {
    if (!waypointReached()){
        x += dx;
        y += dy;
        con.repaintArea((int)x - 25, (int)y - 25, 50, 50);
    }
    else{
        moving = false;
        mover.stop();
    }
}

private boolean waypointReached(){
    return Math.abs(x - currentWaypoint.x) <= speed && Math.abs(y - currentWaypoint.y) <= speed;
}

Other than that, repaint() is only called when placing a new tower.

How can I improve the performance?

score 5 · Accepted Answer · answered Jul 11 '12 at 12:45

Each target runs a Swing Timer to calculate its position. This is the ActionListener it calls:

This may be your problem - having each target/bullet (I assume?) responsible for keeping track of when to update itself and draw itself sounds like quite a bit of work. The more common approach is to have a loop along the lines of

while (gameIsRunning) {
  int timeElapsed = timeSinceLastUpdate();
  for (GameEntity e : entities) {
    e.update(timeElapsed);
  }
  render(); // or simply repaint in your case, I guess
  Thread.sleep(???); // You don't want to do this on the main Swing (EDT) thread though
}

Essentially, an object further up the chain has the responsibility to keep track of all entities in your game, tell them to update themselves, and render them.

Sounds like everyone agrees on this. Thanks, I'll change my design to use something along those lines. — AlcoRhythms, Jul 11 '12 at 16:24

score 3 · Answer 2 · answered Jul 11 '12 at 13:03

I think what might be at fault here is your whole logic of the games setup (no offense intended), As stated in another answer you have different timers taking care of each entities movement, this is not good. I'd suggest taking a look at some gaming loop examples, and adjusting yours to this, you'll notice a great readability and performance improvement a few nice links:

Thanks for the links! As you can probably tell, I'm just starting out with games and I'm in trial-and-error mode ;) — AlcoRhythms, Jul 11 '12 at 16:26

trashgod · Answer 3 · 2012-07-11T16:07:09.750

I was initially wary of the too-many-timer theory. Instances of javax.swing.Timer use "a single, shared thread (created by the first Timer object that executes)." Dozens or even scores are perfectly fine, but hundreds typically start to become sluggish. Depending on period and duty cycle, the EventQueue eventually saturates. I agree with the others that you need to critically examine your design, but you may want to experiment with setCoalesce(). For reference, here's an sscce that you may like to profile.

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Timer;

/**
* @see http://stackoverflow.com/a/11436660/230513
*/
public class TimerTest extends JPanel {

    private static final int N = 25;

    public TimerTest() {
        super(new GridLayout(N, N));
        for (int i = 0; i < N * N; i++) {
            this.add(new TimedLabel());
        }
    }

    private static class TimedLabel extends JLabel {

        private static final Random r = new Random();

        public TimedLabel() {
            super("000", JLabel.CENTER);
            // period 100 to 1000 ms; frequency 1 to 10 Hz.
            Timer timer = new Timer(r.nextInt(900) + 100, new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    TimedLabel.this.setText(next());
                }
            });
            timer.setCoalesce(true);
            timer.start();
        }

        private String next() {
            return String.valueOf(r.nextInt(900) + 100);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(640, 480);
    }

    private void display() {
        JFrame f = new JFrame("TimerTet");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new JScrollPane(this));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TimerTest().display();
            }
        });
    }
}

Great point! The performance was improved a bit, but I'll need to do an overhaul on the design anyway. — AlcoRhythms, Jul 11 '12 at 16:31

score 2 · Answer 4 · edited May 23 '17 at 11:56

2

for painting in the Swing is better (in all cases >= Java5) use Swing Timer exclusivelly
this painting proccess required only one Swing Timer
example about bunch of Stars and one Swing Timer

edited May 23 '17 at 11:56

Community

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answered Jul 11 '12 at 13:25

mKorbel

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score 0 · Answer 5 · answered Dec 08 '12 at 09:33

Try to use one timer for all the targets.

If you have 20 targets then you will also have 20 timers running simultaneously (think about 1000 targets?). There is some expense and the most important thing is each of them is doing the similar job -- to calculate the position -- You don't need to split them. I guess it is a simple task, which will not take you a blink, even running 20 times.

If I got the point, What you want to do is trying to change the positions of all the targets at the same time. You can achieve this by changing all of them in one single method running in one thread.

Java Swing game has poor performance when many sprites are on screen

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