module shellify(thickness = 1) {
    difference() {
        minkowski() {
            children();
            cube([thickness, thickness, thickness], center = true);
        }
        children();
    }
}

module inset_3d(inset) {
    difference() {
        children();
        minkowski() {
            shellify() {
                children();
            }
            cube([inset * 2, inset * 2, inset * 2], center = true);
        }
    }
}

module round_edges(radius) {
    minkowski() {
        inset_3d(radius) {
            children();
        }
        sphere(radius);
    }
}

module round_edges_except_bottom(radius) {
    minkowski() {
        inset_3d(radius) {
            children();
        }
        union() {
            sphere(radius);
            translate([0, 0, -radius])
                cylinder(r = radius, h = radius);
        }
    }
}

module test_object() {
    cube([10, 10, 5]);
    translate([2.5, 2.5, 4.9])
        cube([5, 5, 5]);
}

round_edges_except_bottom(2, $fn = 32)
    test_object();