Warp found some problems with cutaway_textures
(his message in this newsgroup from 09/15/00).

I have similar problem with following:

difference {
  union {
    sphere {<0, 0, 0>, 5 texture {pigment {color blue 1}}}
    sphere {<-5, 0, 0>, 2 texture {pigment {color red 1}}}
  }
  plane {<0, 0, 1>, 0}
  cutaway_textures
}

works good, but

difference {
  union {
    sphere {<0, 0, 0>, 5 texture {pigment {color blue 1}}}
    sphere {<-5, 0, 0>, 2 texture {pigment {color red 1}}}
  }
  union {
    plane {<0, 0, 1>, 0}
    plane {<-1, 0, 0>, 0}
  }
  cutaway_textures
}

ignores cutaway_textures. I think, that the reason is that POV-Ray
automatically asigns default texture to the second union in difference
and cutaway_textures thinks, that this union has texture assigned
with user.

Q: should cutaway_texture ignore all textures in subtracted objects?

I know, that it works good when the planes are not composed to union,
but I have some cases, where I first compose some objects, which
will represent holes to another object in the future (for example
windows in wall, they are added by some macros to one composite) and
after I need cut them from another object in way like

difference {
  object {Actually_composed_wall}
  object {All_window_holes}
  cutaway_textures
}

Disnel

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