POV-Ray

Attached to Project: POV-Ray
Opened by Christoph Lipka - 2010-05-14
Last edited by Christoph Lipka - 2010-08-21

Reflections in multi-layered textures are broken in 3.7 betas, as can be demonstrated with the following scene showing two reflective hemispheres on a checkered plane:

camera {
  location  <1.0, 0.5, -4.0>
  direction 1.5*z
  right     x*image_width/image_height
  look_at   <0.0, 0.0,  0.0>
}

sky_sphere {
  pigment {
    gradient y
    color_map {
      [0.0 rgb <0.6,0.7,1.0>]
      [0.7 rgb <0.0,0.1,0.8>]
    }
  }
}

light_source {
  <0, 0, 0>            // light's position (translated below)
  color rgb <1, 1, 1>  // light's color
  translate <-30, 30, -30>
}

default {
 finish { diffuse 0 ambient 0 specular 0 }
}

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

plane {               // checkered floor
  y, -1
  texture
  {
    pigment { checker color rgb 1 color blue 1 }
    finish{ diffuse 0.8 ambient 0.1 }
  }
}

// left hemisphere
intersection {
  sphere { 0, 1 }
  plane { x, -0.002 }
  texture {
    pigment { color rgb 1 }
    finish{ reflection { 0.5 } }
  }
  texture {
    pigment { color rgbt 1 }
    finish{ reflection { 0.4 } }
  }
  texture {
    pigment { color rgbt 1 }
    finish{ reflection { 0.1 } }
  }
}

// right hemisphere
intersection {
  sphere { 0, 1 }
  plane { -x, -0.002 }
  texture {
    pigment { color rgb 1 }
    finish{ reflection { 1.0 } }
  }
}

Note that the reflection parameters of the left, multi-layered hemisphere sum up to 1.0, i.e. the same value as used in the single layer in the right hemisphere.

The first attached file (test_3.6.2.png), rendered with POV-Ray 3.6.2, shows the expected output: Both hemispheres appear to have the same reflectivity.

The second attached file (test_3.7.0.beta37a.png), rendered with POV-Ray 3.7.0.beta.37a, shows a much brighter left (multi-layered) sphere.

As it turns out, in order to get the expected result with POV-Ray 3.7.0.beta.37a, the reflectivity of each layer must be divided by 3, 2 and 1, respectively (which obviously does not sum up to 1.0):

  ...
  texture {
    pigment { color rgb 1 }
    finish{ reflection { 0.5 / 3 } }
  }
  texture {
    pigment { color rgbt 1 }
    finish{ reflection { 0.4 / 2 } }
  }
  texture {
    pigment { color rgbt 1 }
    finish{ reflection { 0.1 / 1 } }
  }
  ...