algorithm - Calculating frames per second in a game

Question

What's a good algorithm for calculating frames per second in a game? I want to show it as a number in the corner of the screen. If I just look at how long it took to render the last frame the number changes too fast.

Bonus points if your answer updates each frame and doesn't converge differently when the frame rate is increasing vs decreasing.

Answer 1

You need a smoothed average, the easiest way is to take the current answer (the time to draw the last frame) and combine it with the previous answer.

// eg.
float smoothing = 0.9; // larger=more smoothing
measurement = (measurement * smoothing) + (current * (1.0-smoothing))

By adjusting the 0.9 / 0.1 ratio you can change the 'time constant' - that is how quickly the number responds to changes. A larger fraction in favour of the old answer gives a slower smoother change, a large fraction in favour of the new answer gives a quicker changing value. Obviously the two factors must add to one!