An Icosahedron was made in Wings3D, then set fully transparent with a refractive index of 1.33, lit from behind by a parallel light with infinite width. The shadow cast was rendered, imported as terrain and lit by the WpH76_SC HDRI (from the Hypertexture Base set, available at Daz 3D). The terrains are transparent with a refractive index of 0.75. At left the white-grey parts, at right the grey-black parts of the shadow. A terrain made from the shadows cast by an Icosahedron.