-`spacing` : Distance between cells. Default to 1.
-`r`, `delta`, `chamfer` : The outlines of each cell can be moved outward or inward. These parameters have the same effect as [`offset`](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Transformations#offset).
-`region_type` : The initial shape for each cell can be `"square"` or `"circle"`. Default to `"square"`.