Java game application just won't run smooth

Call Me Jimmy

Hey, if anyone has some time on their hands could they please compile these two and take a look at the app?

I'm trying to lay down some fundamentals for a simple action game but I want to get it draw something moving smoothly first.

Currently, in my main game loop I instruct the thread to yeild if the time taken in that loop was less than a certain speed, say 20 ms, but its still slightly jittery, whereas other games have perfect smoothness in movement.

Any help would be greatly appreciated, thanks

PS: Even though I am using a buffer strategy, could the fact that I'm drawing the whole background behind the ball each time be the problem?

Game.java

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.imageio.ImageIO;
import java.util.*;

import java.awt.event.*;
import java.awt.image.*;
import java.awt.*;
import java.net.*;

public class Game extends Canvas{
	public static final int WIDTH = 800;
	public static final int HEIGHT = 600;
	public static final int GAMESPEED = 18;
	public HashMap sprites;
	public BufferStrategy strategy;
	public BufferedImage smiley;
	public long usedTime;
	Ball b;


	public Game(){ // Game Constructor
	    sprites = new HashMap();

	    //create jframe and make it visible
		JFrame jf = new JFrame("Game");
		jf.setBounds(0,0,WIDTH,HEIGHT);
		jf.setVisible(true);
		jf.setResizable(false);
		setIgnoreRepaint(true);

        //connect jframe to panel so it can override 
		//the paint method
		JPanel panel = (JPanel)jf.getContentPane();
		setBounds(0,0,WIDTH,HEIGHT);
		panel.setPreferredSize(new Dimension(WIDTH,HEIGHT));
		panel.setLayout(null);
		panel.add(this);

        //windowlistener for closing the window
		jf.addWindowListener(new WindowAdapter(){
			public void windowClosing(WindowEvent e){
				System.exit(0);
			}
		}); //============== end Game Constructor

		createBufferStrategy(2);
		strategy = getBufferStrategy();

		requestFocus();

	}



	//=====IMAGE LOADING METHOD=====//
	public BufferedImage loadImage(String name){
		URL url = null;
		try{
			url = getClass().getClassLoader().getResource(name);
			return ImageIO.read(url);
		}
		catch(Exception e){
			System.out.println("Couldn't load " + name);
			return null;
		}
	}

    //=====GET SPRITE AND ADD TO LIST OF SPRITES METHOD====//
	public BufferedImage getSprite(String name){
		BufferedImage img = (BufferedImage)sprites.get(name);
		if(img == null){
			img = loadImage("resources/" + name);
			sprites.put(name,img);
		}
		return img;
	}

    //===== INITIALISE WORLD =======//
	public void initWorld(){
		b = new Ball(this);
	}
   
    //=======UPDATE WORLD =========//
	public void updateWorld(){
		b.act();

	}

	//=====PAINT METHOD=====//
	public void paintWorld(){
		Graphics2D g = (Graphics2D)strategy.getDrawGraphics();

		g.setColor(Color.black);    //could this be the jittery problem?
		g.fillRect(0,0,WIDTH,HEIGHT); //could this be the jittery problem?

		b.paint(g);


        //FPS ------------
		if(usedTime > 0)
			g.drawString(String.valueOf(1000/usedTime) + " fps",0,HEIGHT-50);
		else
			g.drawString("--- fps",0,HEIGHT-50);
		//END FPS ----------
		strategy.show();

	}

    //====== MAIN GAME LOOP =======//
	public void gameLoop(){
		usedTime = 1000;
		initWorld();
		while(isVisible()){
			long startTime = System.currentTimeMillis();
			updateWorld();
			paintWorld();
			usedTime = System.currentTimeMillis()-startTime;
			startTime += 10;

			do{
				Thread.yield();
			}
			while(System.currentTimeMillis() - startTime < 17);
		}
	}



	public static void main(String[] args){
		Game game = new Game();
		game.gameLoop();
	}


}

Ball.java

import java.awt.*;

public class Ball{
	protected int x,y;
	protected int width,height;
	protected int vx, vy;
	private Game game;

	public Ball(Game g){
		x = 100; y = 100;
		vx = 5; vy = 0;
		width = 10; height = 10;
		game = g;

		
	}

	public void act(){
		x+=vx;
		if(x< 0 || (x + width) > game.WIDTH){
			vx = -vx;
		}
	}

	public void setVX(int n){
		vx = n;
	}
    
	public void paint(Graphics2D g){
		g.setColor(Color.white);
		g.fillRect(x,y,width,height);
	}

}

Call Me Jimmy

yeah i said I have used a BufferStrategy which is a built in feature of java that does double buffering

bishopLEN

I'm not a game programmer (YET)

Did a bit of tinkering; hope it helps

Lower the vx value to 1

Set the 17 to 5

I was trying other stuff out with Thread.sleep(20) etc. but it's much the same

vx = 1;

while(System.currentTimeMillis() - startTime < 5);

i_am_dogboy

What OS are you using? I had a horrible time with the milli second timer in windows, 2k was the worst but XP was still prety crap. Use the java 3d timer or the nano second time instead see if it helps.

For the timing I'd do something like

long aim = 1000000000L / 60L;
long then, now, diff;
then = System.nanoTime();
while (isVisible())
{
  now = System.nanoTime();
  diff = then - now;
  then = now;
  updateWorld();
  paintWorld();
  try
  {
    Thread.sleep(aim - diff);
  }
  catch(Exception e){}
}

aim is the max amount of time you will sleep for, in this case to allow for 60 frames.
diff is the amount of time taken to update and render the scene

I'm not saying what you're doing is wrong btw, it's just the way I've always done it and it's always worked perfectly for me. All i'm doing is calculating the amount of time it's taken to do the whole frame, and sleeping by the allowed time for a frame - the amount of time taken. This might come up with negatives in Thread.sleep() but there's some extra code i've left out for the sake of simplicity that prevents this, you can just have an if statement if you want...

Your rendering code looks fine so I would think the problem with performance is timing related. This Book covers the topic of java timers in a good bit of depth, it also has excellent examples of rendering code and stuff so have a look at it.

Also look into FSEM(Full Screen Exclusive Mode) to improve performance, it was pretty iffy outside of windows last time I did any fullscreen java 2d apps but that was a good while ago and I would think it's improved since then.

Call Me Jimmy

Hey thanks a lot guys.

I'm on Windows XP yea.
I'll give the nano time thing a try. I think full screen exclusive mode might be tricky but i might give it a try if nano timer aint working as I would hope.

Yea I have a book called "Developing games in java" coming from the States atm so hopefully when that arrives i'll be able to do this perfect.

Call Me Jimmy

Hey there must be a logical error in the nanoTime thing, the game just stops at the start (but is still running). Are you sure that method has worked like that before?

i_am_dogboy

Call Me Jimmy wrote:

Hey there must be a logical error in the nanoTime thing, the game just stops at the start (but is still running). Are you sure that method has worked like that before?

I forgot to convert diff to milli seconds, just change the line

diff = then - now;
to
diff = (then - now) / 1000000L;

Should have spotted that the first time.