I ran across something odd the other day. Is this a bug or is there a
reasonable explaination.

I have a scene with a plane, sphere, transparent  hollow box (rgbf 1) and
ground fog.
If the fog has turbulence then the box is partially visible and casts a
shadow. If the fog has
no turbulence then the box just casts a shadow. If the fog is removed then
box is not
visible and casts no shadow (this is what I would expect in all three cases)

See pics in p.b.i

Eg scene

------------

#version 3.5;
#include "colors.inc"

camera {
  location <0,0.5,-4>
  look_at <0,0,0>
  angle 40
}

fog {
 fog_type   2
 distance   10
 color      rgb 0.6
 fog_alt    10
 turbulence 0.5 // comment this line out and the box disappears
}

light_source {
 <30,30,-30>
 White
}

plane {
  y, -1
  pigment { color rgb <0.7,0.5,0.3> }
}

sphere {
  0, 1
  pigment {
   crackle
   color_map {
    [0.0 Red]
    [1.0 Blue]
   }
   scale 0.5
  }
  translate z*10
}

box {
 <-4,0,0>,<0,2,0.01>
 hollow
 pigment {rgbf 1}
}

----------

Gail
--
#macro G(H,S)disc{0z.4pigment{onion color_map{[0rgb<sin(H/pi)cos(S/pi)*(H<6)
cos(S/pi)*(H>6)>*18][.4rgb 0]}}translate<H-5S-3,9>}#end G(3,5)G(2,5.5)G(1,5)
G(.6,4)G(.5,3)G(.6,2)G(1,1)G(2,.5)G(3,.7)G(3.2,1.6)G(3.1,2.5)G(2.2,2.5)G(9,5
)G(8,5.5)G(7,5)G(7,4)G(7.7,3.3)G(8.3,2.7)G(9,2)G(9,1)G(8,.5)G(7,1)///GS

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