<World>
   <Camera eye="0, 100, 300" look_at="0,0,0" fov="70" />

   <ShaderGroup>
      param float Kd 0.5 [[ int interactive=1 ]];
      param color Cs 0.8 0.2 0.7;
      shader matte layer1;
   </ShaderGroup>
   <Sphere center="-60,30,120"        radius="30" />
   <Sphere center="  0,30,120"        radius="30" />
   <ShaderGroup>
      param float Kd 1;
      param color Cs 0.1 0.9 0.4 [[ int interactive=1 ]];
      shader matte layer1;
   </ShaderGroup>
   <Sphere center=" 60,30,120"        radius="30" />

</World>
