15.40.19  Shading_example 

Shading is produced by the options:
     XY YZ ZX DX DY DZ CROSS RANDOM
If  you  wish to shade the 3 faces differently, you must histogram 3 times
with each pattern you wish.  For example you wish parallel lines on the YZ
face, dots on the ZX face, and crosses on the XY face:
     TD:HISTOGRAM XY CROSS
     TD:HISTOGRAM YZ DX=0.1 DY=0.1
     TD:HISTOGRAM ZX RANDOM DX=1000