%!PS-Adobe-2.0
%%BoundingBox: 0 0 372 180

/w 372 def
/h 180 def

(ps3d.inc) run
(cube.inc) run
(epsetup.inc) run

1 setlinejoin

% ------------------------------------------------

[0 0 5 1] set-eye

/floor [0 1 0 3] def

/A 40 def
/dA 10 def
/t 0 def
/dt 0.1 def

0 0.5 0 translate3d
0.5 dup dup scale3d

{

page-begin

gsave
0.8 0.8 0.8 setrgbcolor
newpath
-2 1 2 {
/i exch def
i -3 -3 moveto3d
i -3  1 lineto3d
} for
-3 1 1 {
/i exch def
-2 -3 i moveto3d
 2 -3 i lineto3d
} for
stroke
grestore

gsave3d
% the shadow
gsave
0.6 0.6 0.6 setrgbcolor

floor light-source plane-project
/shift 0 t dup mul sub def
0 0 shift translate3d
[1 1 1] A rotate3d
-0.5 -0.5 -0.5 translate3d

cube {
  % [ n [P[0] P[1] ... P[n-1]]]
  0 get /f exch def
  /ell f length def
  newpath
  f ell 1 sub get aload pop moveto3d
  f {
    aload pop lineto3d
  } forall
  fill
} forall

grestore
grestore3d

gsave3d

0 0 shift translate3d
[1 1 1] A rotate3d
-0.5 -0.5 -0.5 translate3d
/E get-virtual-eye def
/L get-virtual-light def

cube {
  % [ n [P[0] P[1] ... P[n-1]]]
  dup 
  1 get /n exch def
  0 get /f exch def
  % n = normal function
  /ell f length def
    n 
    E
    dot-product 
  0 ge 
  {
    newpath
    f ell 1 sub get aload pop moveto3d
    f {
      aload pop lineto3d
    } forall
    gsave
      n normalized L 
    dot-product    
    [0.3 0.3 0.8 1 ] 
    shade 0 0 setrgbcolor
    fill
    grestore
    stroke
  } if
} forall

grestore3d

grestore 
showpage

/A A dA add def
/t t dt add def

} loop