math distribute n objects equidistantly with spacing s

I have a set of objects i'm moving across the screen. The are going to be either 200 x 200 or 120 x 120 and will only move right or left in the x direction. I need to calculate the starting positions of the objects

This should be simple math I think, where for objects of size 120x120: (zero is the leftmost edge of the screen)

space=10 (pixels)

object0 starts at -120 )

object1 starts at -240 + space

object2 starts at -360 + space

object3 starts at -480 + space

... object9 starts at -1080 + space

but this isn't working, they get more and more out of alignment the further the calculation goes. When I move them they stay in their out-of-aligned positions, as I'm adding the same amount of开发者_运维问答 motion to each object.

It would also be nice also to compute the starting x positions from any given point instead of manually entering the x positions, accounting for x can be positive or negative.

getPositionOfNth(int objectWidth, int startPosition, int objectNumber, int space){
    return startPosition + objectNumber * (objectWidth + space);
}

Now for your example:

getPositionOfNth(120, 0, 0, 10) == 0
getPositionOfNth(120, 0, 1, 10) == 130
getPositionOfNth(120, 0, 2, 10) == 260
getPositionOfNth(120, 0, 2, 10) == 390
...