Christoph Hormann <chr### [at] gmxde> wrote:
> anson chu wrote:
> > It seems a ray traced (from the camera) through the transparent object
> > (entering and then exiting) and hitting a diffuse surface is treated
> > differently than one that hits the surface directly when considering
> > "radiosity".
>
> Your max_trace_level simply is not high enough, radiosity rays increase
> the trace level like other rays and if they reach max_trace_level no
> more rays are sent.

Actually, this isn't quite complete. If the ray reaches the minimum of
recursion_limit or max_trace_level then no more rays are sent.

The scene file I'm appending shows this effect.

>
> Christoph
>
> --
> POV-Ray tutorials, include files, Sim-POV,
> HCR-Edit and more: http://www.tu-bs.de/~y0013390/
> Last updated 06 Jul. 2004 _____.//^>_*_<^/.______

Bye for now,

Mike Andrews.

// --- radtrans.pov ---

// Radiosity and transparent surfaces
// the only change in each frame is the recursion limit

// run with the following command line:
// +w160 +h120 -a +kff5

global_settings {
  max_trace_level 100
  assumed_gamma 1
  ambient_light 1
  radiosity {
    pretrace_start 1
    pretrace_end   1
    count 100
    nearest_count 10
    error_bound 0.2
    recursion_limit max(frame_number,1)
    low_error_factor 0.01
    gray_threshold 0.0
    minimum_reuse 1e-4
    brightness 1
    adc_bailout 1e-10
    media on
  }
}

camera {
  ultra_wide_angle location y-z*10
  look_at <0,-0.8,-1> angle 35
}

box { -<20,5,20>,<20,-2,20>
  pigment { rgb <.9,.85,.75> }
  finish { diffuse 0.8 ambient 0 }
}

// light source - ambient
sphere { <1,0.5,1>, 0.5
  pigment { rgb 10*<1,.03,.05> }
  finish { ambient 1 diffuse 0 }
}

// light source - media, one extra transparent surface
sphere { <-1,0.5,1>, 0.5
  pigment { rgbf 1 }
  finish { ambient 0 diffuse 0 }
  interior {
    media {
      emission rgb 10*<.03,1,.05>
      samples 1,1 intervals 1 confidence .1
    }
  }
  hollow
}

// simple refractive sphere - two transparent surfaces
sphere { 0, 0.8 translate <-1,-1.2,-1>
  pigment { rgbf 1 }
  finish { diffuse 0.1 ambient 0
    reflection {1 fresnel on}
    conserve_energy
  }
  interior { ior 1.4 }
}

// double refractive sphere - four transparent surfaces
union {
  sphere { 0, 0.8
    pigment { rgbf 1 }
    finish { diffuse 0.1 ambient 0
      reflection {1 fresnel on}
      conserve_energy
    }
    interior { ior 1.25 }
  }
  sphere { 0, 0.7
    pigment { rgbf 1 }
    finish { diffuse 0 ambient 0 }
    interior { ior 1.4 }
  }
  translate <1,-1.2,-1>
}

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