On 01.12.2017 07:58, Bald Eagle wrote:
> This is something that really highlights the do-it-yourself (DIY) nature 
of
> making scenes with POV-Ray - especially the hand-coded SDL type.
> 
> When confronted with a scenario such as Sven's, the instinctual, naive ap
proach
> is to simply subtract a slightly scaled down version of the larger object
.
> The problem is that it's usually a complex shape - so --- exactly where i
s the
> "center"?
> The second problem is that the offset-curve has to be offset in all direc
tions -
> which reveals the true complexity of performing such an operation, and wh
y a
> simple scaling is a naive approach, doomed to certain failure.
> Translate it one way, and "this" overlaps.  Translate it another way, and
 "that"
> overlaps.   It's a no-win situation.
> 
> What would be required with some CSG objects composed of primitives would
 be to
> define a second set of primitives that are scaled relative to their own
> "centers", and then subtract a union of these from the union of the origi
nal
> primitives.
> This of course does not guarantee success - as there is still the "convex
"
> problem.
> Picture an intersecting sphere and cylinder, rather like a "Q" (It inters
ects on
> the typeface of my keyboard).
> You could get a hollow cylinder following the above plan, but as soon as 
you
> subtracted the scaled-down sphere, you'd truncate the portion of the cyli
nder
> inside the sphere.

Yes, exactly that happens with a DIFFERENCE on a complex combined shape
that I currently try to use for a complex shape, that is how i got the
idea to suggest this HOLLOW feature. :-(


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