csg_onion(object, thickness = 0.1)

#Cut and onion a sphere:
generate_ground(material=diffuse(checkercolor="grey20")) %>%
  add_object(csg_object(csg_combine(
    csg_onion(csg_sphere(z=2,x=2,radius=1), thickness = 0.2),
    csg_box(y=1,width=c(10,2,10)), operation = "subtract"),
    material=glossy(color="red"))) %>%
    add_object(csg_object(csg_combine(
      csg_onion(csg_sphere(radius=1), thickness = 0.4),
      csg_box(y=1,width=c(10,2,10)), operation = "subtract"),
      material=glossy(color="purple"))) %>%
    add_object(csg_object(csg_combine(
      csg_onion(csg_sphere(z=-2.5,x=-2.5,radius=1), thickness = 0.6),
      csg_box(y=1,width=c(10,2,10)), operation = "subtract"),
      material=glossy(color="green"))) %>%
 add_object(sphere(y=5,x=5,radius=2,material=light())) %>% 
 render_scene(clamp_value=10,lookat=c(0,-0.5,0),
              lookfrom=c(3,5,10),fov=35)

#Multiple onion layers:
generate_ground(material=diffuse(checkercolor="grey20")) %>%
  add_object(csg_object(csg_combine(
    csg_onion(csg_onion(csg_onion(csg_sphere(radius=1), 0.4), 0.2),0.1),
    csg_box(y=1,width=c(10,2,10)), operation = "subtract"),
    material=glossy(color="purple"))) %>%
  add_object(sphere(y=5,x=5,radius=2,material=light())) %>% 
  render_scene(clamp_value=10,lookat=c(0,-0.5,0),
               lookfrom=c(3,5,10),fov=20)
  
#Onion with dielectric sphere to make a bubble:
generate_cornell() %>%
  add_object(csg_object(
    csg_onion(csg_sphere(x=555/2,y=555/2,z=555/2, radius=150), 5),
    material=dielectric(attenuation=c(1,1,0.3)/100))) %>%
  render_scene(clamp_value=10)
  
#Multiple onion operations to make a bubble within a bubble:
generate_cornell() %>%
  add_object(csg_object(
    csg_onion(csg_onion(csg_sphere(x=555/2,y=555/2,z=555/2, radius=150), 10),5),
    material=dielectric(attenuation=c(1,1,0.3)/100))) %>%
  render_scene(clamp_value=10)