I am doing some block based adaptive filtering and need to reconstruct the signal after filtering. I would like to parameterise the hop length(step size) between blocks so as to experiment with my filter. 

How do I create a window function for constant overlap and add for a window of length N and a hop size of M?

Thanks for any ideas

I see from:

https://www.dsprelated.com/freebooks/sasp/Overlap_...

That:

The Bartlett window is clearly COLA for a wide variety of hop sizes, such as  ,  , and so on, provided  is an integer (otherwise the underlying continuous triangular window must be resampled).

But I don't understand how I resample when varying numbers of samples contribute to a single output sample, i.e. Frame length N = 13, hop length = 3. In this case most of the time 3 blocks contribute to the output sample and sometimes its 4.