I'm somewhat confused by the different results shown below for BoxA and
BoxB. Both boxes are clear, below the camera and light and filled with the
same scattering media. BoxA, which is a shallow box, behaves as I expect -
the light is scattered, some back towards the camera, and hence shows up as
white. BoxB, which is much deeper, shows up as black (with white spots in
ordinary POV, solid black in MegaPOV). I don't understand why the depth of
the box has an impact on scattering media in this situation. After all, if I
look at a cloud, it shows as white irrespective of the physical thickness of
the cloud (provided the cloud is not too thin).

#include "colors.inc"

#declare AorB = 1; // 1=BoxA, any other val for BoxB

light_source{<0,0,0> color White*4 translate <-60, 30, -30>
media_interaction on}
camera{location  <0.0, 5.0, -5.0> look_at   <0.0, 0.0,  0.0>}

// ----------------------------------------

#declare Plain_White_Scattering_Media =
media{
  scattering{1, White}
}

#declare BoxA =  // nice 'n' white in both POV and MP (method 3 for MP)
box
{
  <-10000, -1, -10000>
  < 10000,  0,  10000>
  pigment{rgbf<1,1,1,1>}
  hollow on
  interior{media{Plain_White_Scattering_Media}}
}

#declare BoxB = // completely black (with white spots in POV, pure black in
MP)
box
{
  <-10000, -10000, -10000>
  < 10000,  0,  10000>
  pigment{rgbf<1,1,1,1>}
  hollow on
  interior{media{Plain_White_Scattering_Media}}
}

#if (AorB  = 1)
  object{BoxA}
#else
  object{BoxB}
#end

Post a reply to this message