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Christopher James Huff wrote:
>
> "Ken" <tyl### [at] pacbell net> wrote in message
> news:3DC### [at] pacbellnet...
> > I think it would be astonishing to presume that the average user would
> > know the internal workings of POV-Ray enough to come to the same
> > conclusion :)
>
> OK, point taken, but even without all that, it seems like it should be
> expected that a more complex shape is going to be slower. Being "astonished"
> at it seems very strange...am I missing some meaning and reading things too
> literally?
From the average user vantage point I fail to see where a blob constructed
from cylinders is any more complex than a blob constructed from spheres.
After all, they are both simple basic shapes, are they not?
--
Ken Tyler
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From: Gilles Tran
Subject: Re: Spherical blob components render faster
Date: 2 Nov 2002 20:09:05
Message: <3dc47731@news.povray.org>
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de news: 3dc4429e@news.povray.org...
> "Ken" <tyl### [at] pacbellnet> wrote in message
> news:3DC### [at] pacbellnet...
> > I think it would be astonishing to presume that the average user would
> > know the internal workings of POV-Ray enough to come to the same
> > conclusion :)
>
> OK, point taken, but even without all that, it seems like it should be
> expected that a more complex shape is going to be slower. Being
"astonished"
> at it seems very strange...am I missing some meaning and reading things
too
> literally?
It's just that for the layman a cylinder is not a more complex shape than a
sphere. Even for a non-layman in fact... Both equations are very similar
after all. 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 !!!).
G.
--
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters
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"Ken" <tyl### [at] pacbellnet> wrote in message
news:3DC46EBA.AC7C405A@pacbell.net...
> From the average user vantage point I fail to see where a blob constructed
> from cylinders is any more complex than a blob constructed from spheres.
> After all, they are both simple basic shapes, are they not?
>
exactly.
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From: Christopher James Huff
Subject: Re: Spherical blob components render faster
Date: 2 Nov 2002 22:43:57
Message: <3dc49b7d@news.povray.org>
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"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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On Sun, 3 Nov 2002 10:47:49 -0500, "Christopher James Huff"
<cja### [at] earthlinknet> wrote:
>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.
It's not two caps and a cylinder, actually. It's just that the
distance function used computes the distance to a segment, 's all.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG e-mail : pet### [at] tagpovrayorg
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From: Christopher James Huff
Subject: Re: Spherical blob components render faster
Date: 3 Nov 2002 09:30:42
Message: <3dc53312$1@news.povray.org>
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"Peter Popov" <pet### [at] vipbg> wrote in message
news:4c0asug9885shf979rnrq15pmtksuj117g@4ax.com...
> It's not two caps and a cylinder, actually. It's just that the
> distance function used computes the distance to a segment, 's all.
I know the mathmatical definition of the function, but if I'm reading the
code correctly, it *is* a cylinder section and two hemispheres as far as the
intersection code is concerned, and that's what it looks like to someone who
doesn't know the math.
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> > It's just that the
> > distance function used computes the distance to a segment, 's all.
>
> it *is* a cylinder section and two hemispheres as far as the
> intersection code is concerned
The two are mathematically equivalent anyway. I couldn't think of any way of
calculating the former without using the latter.
- Slime
[ http://www.slimeland.com/ ]
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From: Christopher James Huff
Subject: Re: Spherical blob components render faster
Date: 3 Nov 2002 11:39:40
Message: <3dc5514c$1@news.povray.org>
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"Slime" <slm### [at] slimelandcom> wrote in message
news:3dc550bd$1@news.povray.org...
> The two are mathematically equivalent anyway. I couldn't think of any way
of
> calculating the former without using the latter.
Right, it's the method I used for the cylinder component of my new blob
pattern patch. I don't see any other way to do it.
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I had figured out long ago that it was distance to a line segment. It is
just wacky that there's a 10x difference. I'm creating a smooth blobman jaw
with 30+ blob components and was shocked. at the render difference.
"Christopher James Huff" <cja### [at] earthlinknet> wrote in message
news:3dc53312$1@news.povray.org...
>
> I know the mathmatical definition of the function, but if I'm reading the
> code correctly, it *is* a cylinder section and two hemispheres as far as
the
> intersection code is concerned, and that's what it looks like to someone
who
> doesn't know the math.
>
>
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Greg M. Johnson <gregj:-)56590@ao:-)l.com> wrote:
> I had figured out long ago that it was distance to a line segment. It is
> just wacky that there's a 10x difference. I'm creating a smooth blobman jaw
> with 30+ blob components and was shocked. at the render difference.
Well, if you think about it: What is the function which returns the
distance to a point? And the function which returns the distance to a
line segment (which is a bit more complicated than the distance to a line)?
--
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -
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