/*

This was encountered before, although not specifically about this.
I see it again in beta 15. Documentation clarification might be needed if
this
is simply about using a unacceptable value. It does mention the following:
"The default values for both (alt and offset) are 0.0 so be sure to specify
them if ground fog is used."
However, that seems a on/off situation whereas the red background
appears to be something wrong. Note that if you were to want a ocean of fog
with a level surface this becomes impossible unless a primitive for the sky
object is also used.

This scene shows that when ground fog has zero altitude change the
background color (or blank) is pure red, unless distance is also 0.
The equation for ground fog would have a divide by zero when fog_alt=0
but the red background might be a genuine bug, hence this posting.

bob h April 2, 2002 3.5.beta.15.icl.win32 WinXP 800MHz P3 512MB SDRAM
*/

#declare RedBug=yes; // yes or no

// light_source {y,1} // not needed to show possible bug

camera {location <0,1,-1> look_at <0,1,0>}

 background {rgb <0,0,1>} // doesn't matter if this is used or not

// sky_sphere {pigment {rgb 1}} // likewise this

 plane {y,0 texture {pigment {rgb 1}}} // likewise not a factor

fog {
  fog_type 2
  fog_alt #if (RedBug=yes) 0 #else 1 #end
  fog_offset 1
  color rgb 1 // <0.5,0.5,0.5> // not dependant on color
  distance 9 // make this zero as well and background is okay
}

Post a reply to this message