I know I entered a cubic space version for SCC3, but this one is slightly
different, rather than placing a single junction at the center of a
perfectly reflective cube, this version places 1/6th of a junction at the
corner of a reflective cube.

The 1st attempt at this came out at only 182 bytes so I had some spare
bytes to add improvement, so I rounded the boxes slightly and added
a function to highlight the edges.

(Oddly, in web searching for the original Escher work to compare, I found
more references to POV-Ray versions than the original)