Slow Display due to LCD?

Question

Hi fellow Developers out there...
I have just written a VERY simple game, that displays a ball running over a background. The code was inspired by several other postings that I read. It all works fine (so it is displayed and the ball is moving) but if the ball moves more than 10 pixel per frame, then it gets really ugly: You can then see both sides of the ball flickering quite strongly and its not really a smooth animation.
Now my first guess was that my display was causing these smudges, because I have a Laptop and the reaction time probably isn't so great, but then the effect would look different... However I wanted to get the refresh rate of my monitor in order to sync my framerate with it, but it was zero and my system also has no information about my refresh rate (I have a mac).
The next thing I looked at was the sleep for the remaining time of the frame. I monitored the remaining time and it was nearly allways below zero. Now what am I doing wrong? It can't be so resource consuming to display two cached images...
Here is my code:
import java.awt.Frame;
import java.awt.Graphics2D;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferStrategy;
public class Main implements KeyListener {
    private Frame frame;
    private BufferStrategy strategy;
    private Rectangle screenSize;
    private final static int FPS = 50;
    public Main() {
        GraphicsDevice device = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice();
        frame = new Frame(device.getDefaultConfiguration());
        frame.setUndecorated(true);
        frame.setIgnoreRepaint(true);
        frame.addKeyListener(this);
        device.setFullScreenWindow(frame);
        screenSize = frame.getBounds();
        frame.createBufferStrategy(2);
        strategy = frame.getBufferStrategy();
        //Objekte
        Sprite background = new Sprite("background");
        Sprite ball = new Sprite("ball");
        int counter = 0;
        while (true) {
            long startTime = System.currentTimeMillis();
            counter = counter + 8;
            if (counter > screenSize.width)
                counter = 0;
            Graphics2D graphics = (Graphics2D) strategy.getDrawGraphics();
            graphics.drawImage(background.render(), null, null);
            graphics.drawImage(ball.render(), counter, screenSize.height - 220, null);
            graphics.dispose();
            strategy.show();
            try {
                long remainingTime = (1000 / FPS) - (System.currentTimeMillis() - startTime);
                if (remainingTime > 0)
                    Thread.sleep(remainingTime);
            } catch (InterruptedException e) {
    public void keyTyped(KeyEvent e) {
        //nichts tun...
    public void keyPressed(KeyEvent e) {
        if (e.getKeyCode() == KeyEvent.VK_ESCAPE)
            System.exit(0);
    public void keyReleased(KeyEvent e) {
        // nichts tun...
    public static void main(String[] args) {
        Main m = new Main();
public class Sprite {
    private Image frame;
    public Sprite(String name) {
        if (frame == null)
            load(name);
    private void load(String name) {
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        frame = toolkit.getImage(getClass().getResource("/images/" + name + ".gif"));
    public Image render() {
        return frame;
}Thanx for your advice...
flowcoder2

Answer 1

System.currentTimeMillis() is a horrible timer, which you can't even use for measuring network latency. It's resolution equals the operating system's tick time (win9x 50-55msec, macos/win2k/winxp 10msec, linux 1msec... iirc). So yea with a basically empty loop you'll usually get 0 msec as difference here (the next bigger step is the tick interval).
There are native timer libs and well with 1.5 you have finally a usable hi res timer (System.nanoTime)... unfortunately mac's 1.5 isn't out yet.
Btw Thread.sleep isn't really accurate, too. You can get it down to about 5msec on all operating systems, but it can always take longer than that (you just tell the OS that you would like to continue your stuff in 5msecs and there is no guarantee that it will be in time).