skipping certain number of frames on a timeline

Question

i have a mathematical problem which is a bit hard to describe, but i'll give it a try anyway.

in a timeline, i have a number of frames, of which i want to skip a certain number of frames, which should be evenly distributed along the timeline.

for example i have 10 frames and i want to skip 5, then the solution is easy: we skip every second frame. 10/5 = 2

if (frame%2 == 0)
    skip();

but what if the above division does result in a floating number?

for example in 44 frames i want to skip 15 times. how can i determine the 15 frames which should be skipped?

bascially i am looking for an algorithm that distributes that 15 frames as evenly as possible along the 44 frames. it will probably look like something like skipping after 2 and then after 3 frames alternately.

thanks!

Answer 1

You could keep an additional floating point value, t, that corresponds to the next frame to skip, and update it every time you skip. Like this:

int frame_num = 44; 
int skips_num = 15; 
double dt =((double)(frame_num))/skips_num;
double t = 0.0;
...
// then, in your loop
if (frame == (int)t) {  
  skip();   
  t += dt; 
}

Answer 2

You can obviously not always do it really evenly in case the number of frames you want to skip is not a divisor of the total number of frames. So if it is important to always skip at least the number of frames you want, perform a floor on the division (totalFrames/framesToSkip).

Having said that, you can apply the same trick as you proposed.

if (totalFrames % floor(totalFrames/framesToSkip) == 0)
    skip();

Note that in the case of 44 and 15 you skip much more than 15. The other posibility is to ceil instead of floor, in that case you wont skip 15 frames but 14 frames.

Yet another solution is to do a round to the nearest integer, this is a better approximation, however, you sometimes skip more than wished and sometimes less than wished but on average you have better results