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Average fps

Started by Ruudje Nov 28, 2003 at 9:02 AM 1 reply 450+ views

Original Post

Nov 28, 2003 at 9:02 AM

Hey all, Id like to calculate the AVERAGE framerate aswel as the normal fps. The normal fps is working, but the average isnt. Im trying to do so like this:

// global
long active = 0; // amount of seconds the program is active
int average_fps = 0; // duh

// in the loop
..
active++;
average_fps = (average_fps + fps) / active;
..

By the time of the line active++; fps contains the current framerate. Im not sure why, but something is going wrong. If I let my program run for a while, the average_fps keeps getting lower and lower...

Enigma

188

Enigma

Nov 28, 2003 at 9:13 AM

OK, lets look at this:
Assume constant fps of 100.
t = 0: active = 0, average_fps = 0.
t = 1: active = 1, average_fps = (0 + 100) / 1 = 100
t = 2: active = 2, average_fps = (100 + 100) / 2 = 100
t = 3: active = 3, average_fps = (100 + 100) / 3 = 66.67
t = 4: active = 4, average_fps = (66.67 + 100) / 4 = 41.67

Now I'm going to guess what you mean by 'normal' and 'average' fps:
normal fps = fps at any particular instant
average fps = total frames rendered / total time taken

For this your average_fps formula should be:
average_fps = ((previous_average_fps * number_of_seconds_of_previous_fps) + (current_fps * number_of_seconds_of_current_fps)) / total_time_so_far
or:
average_fps = ((average_fps * (active - 1)) + fps) / active

Enigma

EDIT: just realised I'd said "Assume constant fps of 60.", but used 100!

[edited by - Enigma on November 28, 2003 12:17:43 PM]

Ruudje

Author

Ruudje

Nov 28, 2003 at 9:20 AM

omg cant believe i didnt realise that

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