Show 3D polyhedra using only the tk canvas
This code displays 3d polyhedra in shaded or wireframe mode. It uses only the tk canvas. The illumination model is a simple flat shading model [http://en.wikipedia.org/wiki/Shading#Flat_shading]. The color intensity of a face is proportional to the angle between its normal and a light direction.
This (pythonized) Tcl/Tk code is based on polyhedra.tcl (2005) by Gerard Sookahet, Tcl wiki [https://wiki.tcl-lang.org/page/3D+polyhedra+with+simple+tk+canvas]