Why are my game ticks longer than expected?

Question

I was working on my game, adding stuff to it, when I noticed my ticks were in the low 50's when I had set it to do a constant 60. This is my run method.

public void run() {
    init();
    long lastTime = System.nanoTime();
    final double amountOfTicks = 60.0;
    double ns = 1000000000.0 / amountOfTicks;
    double delta = 0;
    int updates = 0;
    int frames = 0;
    long timer = System.currentTimeMillis();

    while (running){
        long now = System.nanoTime();
        delta += (now - lastTime) / ns;
        lastTime = now;
        if (delta >= 1) {
            gameUpdate();
            updates++;
            delta--;
        }

        try {
            Thread.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        gameRender();
        frames++;

        if (System.currentTimeMillis() - timer > 1000) {
            timer += 1000;
            frame.setTitle(title + "   |   " + "Frames Per Second: "
                    + frames);
            System.out.println(updates + " Ticks, " + frames + " Frames");
            updates = 0;
            frames = 0;
        }
    }
    stopGame();
}

I've tried removing all the code I added before this occurrence happened and it didn't help. Suggestions would be great!

Answer 1

Delete the Thread.sleep() call (assuming you're on a desktop machine and have power to spare!).

In general you never sleep in your game loop (except on Android, where there appears to be no other choice). The bad thing about Thread.sleep is it is unpredictable and may cause your game to give up exec time for longer than 16ms, which is the maximum time a frame can take to complete a frame at 60 fps.

If there is too much time at the end of your loop, you usually can let the GPU VSYNC keep you at 60 FPS. If VSYNC is off, then you busy wait, basically in the form of a loop like:

while( getTimeDeltaThisFrame() <= 16 ms )  ;  // keep "spinning" until
                                              // 16ms have passed.

Note that busy waiting on a portable device is going to burn a lot of battery, and you may have to allow a sleep call and step down to a lower frame rate there.

Answer 2

Make sure never to have the Thread.sleep(). It takes time for a render to complete... That's why the FPS is lower than expected.