Stop flickering in swing when i repaint too much

Question

I am making an RPG with a tilemap. To generate the tilemap i loop through a 2 dimensional array but that means that when I repaint I have to do that each time. If I repaint too much the screen flickers how could I stop this.

package sexyCyborgFromAnOtherDimension;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Timer;
import java.util.TimerTask;

import javax.swing.JPanel;

@SuppressWarnings("serial")
public class Game extends JPanel
{
    KeyLis listener;
    int mapX = 20;
    int mapY = 20;
    boolean up = false;
    boolean down = false;
    boolean right = false;
    boolean left = false;
    String[][] map;

    public Game()
    {
        super();
        try 
        {
            map = load("/maps/map1.txt");
        } 

        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        listener = new KeyLis();
        this.setFocusable(true);
        this.requestFocus();
        this.addKeyListener(listener);

        Timer timer = new Timer();
        TimerTask task = new TimerTask() 
        {
            @Override
            public void run() 
            {
                if(up)
                {
                    mapY++;
                    repaint();
                }

                if(down)
                {
                    mapY--;
                    repaint();
                }

                if(right)
                {
                    mapX--;
                    repaint();
                }

                if(left)
                {
                    mapX++;
                    repaint();
                }
            }
        };
        timer.scheduleAtFixedRate(task, 0, 10);
    }

    public void paint(Graphics g) 
    {
        super.paintComponent(g);
        setDoubleBuffered(true);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        for (int x = 0; x < map.length; x++) 
        {
            for (int y = 0; y < map[x].length; y++) 
            {
                switch(map[x][y])
                {
                case "0":
                    g.setColor(Color.GREEN);
                    break;
                case "1":
                    g.setColor(Color.GRAY);
                    break;
                }

                g.fillRect(y*20+mapX, x*20+mapY, 20, 20);
            }
        }
        g.setColor(Color.BLACK);
        g.fillRect(400, 400, 20, 20);
    }

    String[][] load(String file) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(getClass().getResourceAsStream(file)));
        int lines = 1;
        int length = br.readLine().split(" ").length;
        while (br.readLine() != null) lines++;
        br.close();
        BufferedReader br1 = new BufferedReader(new InputStreamReader(getClass().getResourceAsStream(file)));
        String[][] map = new String[lines][length];
        for (int i = 0; i < lines; i++)
        {
            String line = br1.readLine();
            String[] parts = line.split(" ");
            for (int y = 0; y < length; y++)
            {
                map[i][y] = parts[y];
            }
        }
        br1.close();
        return map;
    }

    private class KeyLis extends KeyAdapter 
    {   
        @Override
        public void keyPressed(KeyEvent e) 
        {
            switch (e.getKeyCode())
            {
            case KeyEvent.VK_UP:
                up = true;
                break;
            case KeyEvent.VK_DOWN:
                down = true;
                break;
            case KeyEvent.VK_LEFT:
                left = true;
                break;
            case KeyEvent.VK_RIGHT:
                right = true;
                break;
            }
        }

        @Override
        public void keyReleased(KeyEvent e) 
        {
            switch (e.getKeyCode())
            {
            case KeyEvent.VK_UP:
                up = false;
                break;
            case KeyEvent.VK_DOWN:
                down = false;
                break;
            case KeyEvent.VK_LEFT:
                left = false;
                break;
            case KeyEvent.VK_RIGHT:
                right = false;
                break;
            }
        }
    }
}

Thank you for your help

Edit

Using javax.swing.Timer removes all flickering even with a 10 ms delay.

@Qwerky indeed nice - but not complying to java naming conventions — kleopatra, Jul 31 '13 at 09:02
@kleopatra Ok i will change it to com.sexyCyborgFromAnOtherDimension. — sanchixx, Jul 31 '13 at 09:04
the domain is not the point: package names shouldn't contain uppercase letters :-) — kleopatra, Jul 31 '13 at 09:06
several thingies wrong with your code (may be unrelated to the problem) a) override paintComponent for custom painting (_not_ paint) b) don't change the component's state in a paint method c) favour KeyBindings over KeyListeners Other than that: 10ms looks like a very tight loop... — kleopatra, Jul 31 '13 at 09:17
good point because 10ms looks like to overload latency for standard Native OS — mKorbel, Jul 31 '13 at 09:20

score 7 · Accepted Answer · edited May 23 '17 at 12:14

A number of small things jump out at me.

Firstly. You might be better using javax.swing.Timer instead of java.util.Timer, this will at least allow the events to flow a little better.

Secondly, 10 milliseconds is to short a time period, seriously, you don't need 100fps, 60fps is about 17 milliseconds, I normally use 40 milliseconds for 25fps. This might give the EDT some breathing room to actually respond to the repaint requests.

Thirdly, you should be using paintComponent instead of paint. It's low enough in the call chain to guaranteed to be double buffered

Fourthly, you should avoid calling any method that might reschedule a repaint (like setDoubleBuffered for example, to this in the constructor if you must, but, Swing components are double buffered by default)

Fifthly, where possible, paint all "static" or slow changing content to a backing buffer and paint that instead. This will increase the speed at which paint can work as it doesn't get stuck in a lot of small loops.

You may want to take a look at Painting in AWT and Swing for more details about the paint process

Some additional examples...

Swing animation running extremely slow - was able to go from 500 elements up to 4500 elements moving on the screen at one time - talks about resource management as well
Java Bouncing Ball
How to make line animation smoother?
the images are not loading

And because kleo scares me (and it's also a good idea), you should also take a look at How to use Key Bindings, which will solve your focus issues with the KeyListener

@sanchixx Then you're still doing something wrong, there should no flickering. If you take time to look over some of the examples I linked, you should find that none of them suffer from any flickering at all — MadProgrammer, Jul 31 '13 at 11:16

Qwerky · Answer 2 · 2013-07-31T09:26:18.807

0

You have set double buffering on the panel, but the things you are drawing on it yourself are not being double buffered. Calling setDoubleBuffered(true) only applies buffering for child components of the container.

You need manually buffer stuff you draw yourself.

I would suggest moving away from a JPanel and use a Canvas instead. Have a look at how a Canvas is used with a buffer strategy in this class, where it can handle hundreds of things being drawn on screen with perfect smoothness and no flickering (the game runs on a 10ms sleep loop too).

edited Jul 31 '13 at 09:26

answered Jul 31 '13 at 09:07

Qwerky

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Or use `paintComponent` instead of `paint` where it is double buffered...and using `javax.swing.Timer` wouldn't hurt either – MadProgrammer Jul 31 '13 at 09:09
not really true: the RepaintManager bubbles up repaint request to the nearest parent that is doubleBuffered. JPanel is so by default, even if it set to not doubleBuffered, the rootPane is :-) – kleopatra Jul 31 '13 at 09:12
2

@MadProgrammer - just noticed he's calling `super.paintComponent()` from inside `paint()` :S – Qwerky Jul 31 '13 at 09:16
@Qwerky Well, that's going to screw things up :P – MadProgrammer Jul 31 '13 at 09:17
@kleopatra Thanks for the additional info, nice to know – MadProgrammer Jul 31 '13 at 09:17

score -1 · Answer 3 · answered Jul 31 '13 at 09:08

Not really sure if it solves your problem, but you can consider to use a 1dimensional array.

when int width; is the width of your screen/tile/whatever you loop and int height is the height you coud do the following:

instead of, what you do:

for(int x = 0; x < width; x++)
{
    for(int y = 0; y < height; y++)
    {
        // dosomething with your array
        myarray[x][y];
    }
}

you could go through this way

for(int y = 0; y < height; y++)
{
    for(int x = 0; x < width; x++)
    {
        // dosomething with your array
        myarray[x + y * width];
    }
}

That would not solve my problem and I like using a 2 dimensional array. — sanchixx, Jul 31 '13 at 09:12

Stop flickering in swing when i repaint too much

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3 Answers3

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