"Gilles Tran" <git### [at] wanadoofr> wrote in message
news:3dc47731@news.povray.org...
> It's just that for the layman a cylinder is not a more complex shape than
a
> sphere.

Hmm...maybe I'm just looking at it differently, but having two spherical
caps and a cylinderical section seems intuitively more complex than a
sphere.


> Even for a non-layman in fact... Both equations are very similar
> after all.

And for an isosurface function with axis-aligned cylinders, a cylinder
function is simpler...understandable confusion there. There are other
complications in the case of blob components which I don't expect "laymen"
to understand, but isosurfaces are more of an advanced user feature anyway.


> I don't dispute the fact that it's computationally more
> expensive, but the difference in rendering time reported by Greg is really
> big (x 10 !!!).

That did catch me off guard, it seemed suspicious until I took bounding into
account, which I don't expect the average user to think of. The fact that
one is slower than the other just seems pretty expected to me, I'd be very
surprised if any two primitives were exactly the same as far as speed, and
without looking at the math I'd guess that the cylinder is the slower one.

An idea: use "hierarchy off" and compare the speeds then...it should
eliminate the bounding differences, leaving only the blob calculation
differences. If my guess is right, the sphere component blobs will slow down
more than the cylinder component ones, bringing them closer to equal.

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