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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"Disnel" <dis### [at] hlavacek-partnercz> wrote in message
news:39F00638.36C4E0F6@hlavacek-partner.cz...
>
> 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

Think you may be right, the union probably doesn't adhere to a proper entity
for that purpose.  Must be that CSG isn't applicable to the cutaway_textures
feature, doing it only on a per primitive basis.

Bob

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"Bob H." wrote:
> 
> "Disnel" <dis### [at] hlavacek-partnercz> wrote in message
> news:39F00638.36C4E0F6@hlavacek-partner.cz...
> >
> > 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
> 
> Think you may be right, the union probably doesn't adhere to a proper entity
> for that purpose.  Must be that CSG isn't applicable to the cutaway_textures
> feature, doing it only on a per primitive basis.
> 
> Bob

I can remember all holes in array instead "storing" them in union,
but it is more complicated and I am limited with some fixed array
size .... possible growing array will be very useful ;-).

Disnel

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"Disnel" <dis### [at] hlavacek-partnercz> wrote...
>
[clip]
> 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.

This sounds like a bug.  I don't have time to try to fix it now,
unfortunately.  I'll look into it, though.  It probably has something to do
with the fact that unions get split up.

-Nathan

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