ex indices that constitute the convex hull
            hull = [group[i] for i in convex_hull([layout[idx] for idx in group])]

            # Calculate the preferred rounding radius for the corners
            corner_radius = 1.25 * max(vertex_builder[idx].size for idx in hull)

            # Construct the polygon
            polygon = [layout[idx] for idx in hull]

            if len(polygon) == 2:
                # Expand the polygon (which is a flat line otherwise)
                a, b = Point(*polygon[0]