How do you measure fps?

General Discussions
#1

How do you guys display FPS to the screen?

int fps = 60;
t0 = system.nanoTime();
//...lots of rendering
//..
//..
t1 = system.nanoTime();
long delta = ((1E+9)*1.0/fps) - (t1-t0);
g.drawString("FPS:"+ (1E+9)*1.0/delta, 0,0);
buffer.show();
//Sleep
Thread.sleep(delta)

This is how I currently do it and there are so many problems with it:

  • Delta may be negative due to bad resolution
  • Delta does NOT take into account time spent calling g.drawstring and buffer.show
  • The sleep may be accurate within margins of error by calling system.nanoTime() inside sleep() but this makes for inaccurate display
  • If t1 is too long delta becomes negative. Do you play catchup with the framerate by sleeping a shorter time next iteration?

I see no way of circumventing the second point, display to console would be much easier, you could wrap all of it in a method, measure time between each method-calls and print it to console. But any displayed FPS must take the delta THEN display it.

#2

For your second point you can do this (making sure to initialise t0 to something):

int fps = 60;
//...lots of rendering
//..
//..
t1 = system.nanoTime();
long delta = ((1E+9)*1.0/fps) - (t1-t0);
t0 = system.nanoTime();
g.drawString("FPS:"+ (1E+9)*1.0/delta, 0,0);
buffer.show();
//Sleep
Thread.sleep(delta)

I usually just literally count the number of frames it displays in a second (the fps gets updated every second).

#3

I just count the number of times per second the GLEventListener.display() method is called. And I use System.currentTimeMillis() - with each frame 16 - 40 ms to render I don’t think precision is that much of an issue.