SkinMan can make complex shapes not only "Shape" primitive, but also "Operation" of the child primitive. at first, you need to make a parent - child primitives to use operation by Treeview.
Above, the blue circle is a child primitive of the red rectangle.
The "Operation" parameter of the blue circle to "Shape+"...
The both shape is added. Shadows / Textures of the child is ignored, and take a part of the parent primitive.
In the case of the "Shape-"
Cutting out the child primitive.
In the case of the "Shape*"
remained only the overlayed part.
A sample of the "Operation". made by Polygon and three circle