Game loop not accurate. How can I make a better one ?

Newbie & Debugging Questions
#1

This game loop that I have implemented is not constant. I want my program to run at 60 frames per second. Basically I need to make the Thread sleep for 17 milliseconds after each frame, but sometimes it sleeps more that 17 milliseconds, this makes my game jittery. What should I do to make a more efficient game loop?

public class GamePanel extends JPanel implements Runnable {

	
	@Override
	public void run() {
		currentTime = System.currentTimeMillis();
		prevTime = currentTime;
		while(true) {
			repaint();
			upd();
			try {
				Thread.sleep(17);
			} catch(InterruptedException e) {
				e.printStackTrace();
			}
			prevTime = currentTime;
			currentTime = System.currentTimeMillis();
			delta = currentTime - prevTime;
			System.out.println(delta);
		}
	}
}
#2

Check out this guide! http://www.java-gaming.org/index.php?topic=24220.0 :slight_smile:

#3

actually it is okay, but you have to factor the delta value in your update() method.

#4

just divide delta through 17 and you have your update factor.
For example:

player speed is 10. if delta is 17 (optimum) you calc:

player.position += 10 * 17 / 17

so plus ten. if your game sleeps longer for example delta = 34,
delta / 17 is 2 and your player would move twice as fast in this frame.

#5

Actually it is not ok.

When it says
Thread.sleep(17)

you are assuming you render takes 0ms - which is most probably not correct.

The sleep should be 17 - time to render. So you should tke note on how long it takes to render stuff and reduce that from the sleep time afterwards.

#6

That just makes it more complicated.
You already have your delta calculated , just check to see if the delta >= 60/1000000000 , this is if you are using nano_time(); this will render at 60 - 58 FPS just modify the value at will.

#7

a good and solid timer would be nice to have … but it’s not gonna happen :frowning: …

using [icode]Thread.sleep()[/icode] is ok, using [icode]Thread.yield()[/icode] is not that good … but helps with “jerky” loops.

whatever you do … try using [icode]Thread.speep(1)[/icode] and then try to find a threshold when to use [icode]Thread.yield()[/icode] to skip the last tiny bit of time to keep the loop stable.

afaik that’s the only way to get it to do someting useful.

#8

You can take a look at what LWJGL uses: https://github.com/LWJGL/lwjgl/blob/master/src/java/org/lwjgl/opengl/Sync.java