What you're suggesting is fine, as these are common problems
when handling CSG, but the solution is far easier:

You're differencing two objects, right? One is a glass-lens,
with the required texture. You're cutting parts away with
a box. What kind of texture does it have?
It's the black default texture...

When doing CSG where I just want to cut some material
into a proper form, I do all the CSG first, and apply the
textures later. When cutting a portion away, that surface is,
when being raytraced, actually the surface of the cut-away
object, not the original object's surface. Thus, it uses the
texture of the other object.

Try it. Take a red sphere and cut one half away with a blue
box.


-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


> >
> > >   I'm trying to simulate a pair of glasses with a cracked lens.  My
first
> > > thought was to split the lens into several pieces, and then, when put
> > > together, they would nicely simulate the broken glass of the lens.
The
> > > problem is that in the intersection between the pieces, I'm getting a
black
> > > area in my rendering.  Reading another post, I first tried overlapping
the
> > > two pieces, and then tried separating them with a space, and finally
tried
> > > putting them flush.  All three yeilded the black area in the
interface.
> >
> > Have you tried a higher max_trace_level?
> > Well, you didn't mention it, so you probably haven't. Put something like
> > "global_settings {max_trace_level 20}" at the beginning of your scene.
> > Basically, this tells POV to go through more transparent or reflecting
> > surfaces before it stops tracing rays.
>
> Oh, and you should probably use the air-gap method. It will simulate an
> actual crack more closely, though if they are too close you may get
> precision problems. There probably isn't a really accurate way of doing
> this in POV, but another way might be to use a height field, mesh, or
> some other irregular flat object for the crack surface, and clip it to
> the lens object. This would avoid the CSG you are using, and might
> simplify more complex cracks, though it doesn't accurately model real
> cracks.
>
> -- 
> Christopher James Huff <cja### [at] earthlinknet>
> http://home.earthlink.net/~cjameshuff/
> POV-Ray TAG: chr### [at] tagpovrayorg
> http://tag.povray.org/


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