Wasn't it Omega who wrote:
>Tim Nikias v2.0 wrote:
>>Povray makes use of pseudo-random streams, but for normals, it uses the
>>inbuilt patterns, and they're not random at all. And even if you use the
>>rand()-stream to actually randomize the "location" of the pattern, then it
>>will stay the same as long as the seed isn't changed. I'm not too sure about
>>different platforms though, some Guru needs to answer that.
>
>Ok, as long as I have the assurance that the bump pattern won't change if I
>don't move the sphere, it's fine.

You just have to be careful about how you move the object. In this first
example the two spheres have exactly the same bumps:

sphere {0,1 pigment {rgb 1}
 normal {bumps scale 0.1}
}

sphere {0,1 pigment {rgb 1}
 normal {bumps scale 0.1}
 translate <2,0,0>
}


But in this second example the patterns of the bumps are different.

sphere {0,1 pigment {rgb 1}
 normal {bumps scale 0.1}
}

sphere {0,1 pigment {rgb 1}
 translate <2,0,0>
 normal {bumps scale 0.1}
}


What happens is that POV has a sort of random bump field that pervades
the whole of 3d space, and which becomes visible only when you put a
surface in that space. In the first example, the two spheres pick up
their bumps from the same place in the 3d bump field, and then one of
them moves sideways taking those bumps with it.

In the second example the sphere moves sideways first, and then has
different bumps from the new location applied to it.

Syntax like the following is used in animations where you want the
object to keep the same pattern as it moves through space, like real
solid objects do. You can be assured that this will always keep the same
pattern - if it didn't it wouldn't be possible to represent a realistic
textured object in a POV animation.

sphere {0,1 pigment {rgb 1}
 pigment {bozo scale 0.1}
 normal {bumps scale 0.1}
 translate <2*clock,0,0>
}

-- 
Mike Williams
Gentleman of Leisure

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