background {color rgb<1,1,1>}
camera {
location <5, 3, 1>
look_at <0, 0, 0>
angle 35
}
light_source { <5, 4, 3> rgb<1, 1, 1> }

#declare grain1 =
  texture { pigment { rgb <1,0,0> } finish {ambient 0.2} }

difference
{
  mesh
  {
     triangle {<0,0,0>, <1,0,0>, <0,1,0>
     texture {grain1}}

     triangle {<0,0,0>, <1,0,0>, <0,0,1>
     texture {grain1}}

     triangle {<0,0,0>, <0,1,0>, <0,0,1>
     texture {grain1}}

     triangle {<1,0,0>, <0,1,0>, <0,0,1>
     texture {grain1}}

     inside_vector <1,1,1>
  }

  box{ <0.5,-0.5,-0.5>, <1.2,1.2,1.2>}
}