Java Game Timer Issue! Help

[smithywill]

Hey guys

Got a bit of a problem, I have created this little pong pong style Java app and I thought everything was working fine however when I tried it at the Universitys computers it was a lot slower then normal.

I have a feeling it has to do with the timer which calls the repaint() method every 3 milliseconds:

public void actionPerformed(ActionEvent e)
{
		
	box.move();
	ball.move();
	checkcollision();
	score.setText(""+scoreno);
	repaint();
		
}

Any ideas why the speed of the game varies from PC to PC?

Cheers

Smithywill

[mrmatt1111]

You cannot guarantee constant intervals of time. You need to take the delta time (the difference in time) to determine how far to move something.

Lets say you want to move 5 pixels every 100ms and you try to update every 20ms.

Time for each Tick

tick 0: 19ms;
tick 1: 25ms;
tick 2: 35ms;
tick 3: 20ms;

double standardTimeInterval = 100.0;   //100ms
double pos = 0.0; //position of your object
double velocity = 5.0;
long lastTime = 0;
...
if(lastTime == 0) 
   lastTime = System.currentTimeMillis();
double dt = (System.currentTimeMillis()-lastTime)/standardTimeInterval;
lastTime = System.currentTimeMillis();

pos +=  velocity * dt;

Distance traveled after each tick

tick-1: 0 pixels
tick 0: 0.95 pixels
tick 1: 2.2 pixels
tick 2: 3.95 pixels
tick 3: 4.95 pixels

[Klauspinto]

The resolution of Java timers is not very accurate because Java doesn't play well with Windows processor in a multiple processor architecture. It seems that Windows will sleep processes in different areas of the processor or even in different processors effectively blacking out the timer.