Consider these polygons:

![Consider these polygons](https://i.stack.imgur.com/jSeLV.png)

For reasons of simplicity I only consider triangles or polygons with 4 vertices.
These shapes are specified by the vertices, the output of the program should be modified vertices.

I am trying to find an algorithm to create a space between the polygons, the colored area depicts the space:

![polygons with space](https://i.stack.imgur.com/yQD6h.png)

I have tried these things:

* scaling each polygon around it's center of gravity
* scaling the bounding box of each polygon

None of those worked. 

I am thinking of an algorithm to modify the corner points of each polygon to create the equidistant space.

What would be a feasible algorithm for this problem?