4.0 * Int( x / 4.0 ) is x rounded to a multiple of 4.
The idea is that Int() rounds to integer, i.e. a multiple of 1.
So you scale x down so the gap is 1, round it, then scale back up to multiple of 4.
The idea is that Int() rounds to integer, i.e. a multiple of 1.
So you scale x down so the gap is 1, round it, then scale back up to multiple of 4.