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I found this page on the Japanese povray webring.
http://www.cs-w.com/~earth/material/isopattern.htm
There is here the use of the cells pattern in a way that does not give
diffuse=0 on the edges of step functions. I will study the source code,
but the reason why it looks so good hasn't hit me yet. Any clues?
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"Greg M. Johnson" wrote:
>
> I found this page on the Japanese povray webring.
>
> http://www.cs-w.com/~earth/material/isopattern.htm
>
> There is here the use of the cells pattern in a way that does not give
> diffuse=0 on the edges of step functions. I will study the source code,
> but the reason why it looks so good hasn't hit me yet. Any clues?
I'm not totally sure what you mean by diffuse=0 but i suspect you meant the
problems occuring with abrupt steps in the pattern.
You can see in the source code, that the critical patterns all use higher
max_gradient values (20/50) and there are still errors occuring although not
very strong. On 'isopattern2.htm' they are even better visible.
Christoph
--
Christoph Hormann <chr### [at] gmx de>
Homepage: http://www.schunter.etc.tu-bs.de/~chris/
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In article <3A06F4C7.3AB43D80@my-dejanews.com>,
gre### [at] my-dejanews com wrote:
> There is here the use of the cells pattern in a way that does not give
> diffuse=0 on the edges of step functions. I will study the source code,
> but the reason why it looks so good hasn't hit me yet. Any clues?
As I have mentioned before: I think the problem is not that the diffuse
is being set to 0(which sounds impossible), but that there is a problem
calculating the normal for these functions. If the resulting normal is
bad(containing NaN or something) or is just wrong, the lighting
calculations will not work properly.
--
Christopher James Huff
Personal: chr### [at] mac com, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tag povray org, http://tag.povray.org/
<><
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From: Greg M Johnson
Subject: Re: Diffuse==0 in step functions, problem solved?
Date: 7 Nov 2000 08:27:55
Message: <3a08035b@news.povray.org>
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Chris Huff wrote:
> In article <3A06F4C7.3AB43D80@my-dejanews.com>,
> gre### [at] my-dejanews com wrote:
>
> > There is here the use of the cells pattern in a way that does not give
>
> As I have mentioned before: I think the problem is not that the diffuse
> is being set to 0(which sounds impossible), but that there is a problem
> calculating the normal for these functions. If the resulting normal is
> bad(containing NaN or something) or is just wrong, the lighting
> calculations will not work properly.
Thanks for the reply, but the point is that in this gentleman's (Makoto Mukui)
image, there is no such problem.
http://www.cs-w.com/~earth/material/isopattern.htm
Thus it is not a fundamental, inescapable problem with step functions in
to sleep.
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In article <3a08035b@news.povray.org>, "Greg M. Johnson"
<"gregj;-()"@aol.c;-()om> wrote:
> Thanks for the reply, but the point is that in this gentleman's
> (Makoto Mukui) image, there is no such problem.
> Thus it is not a fundamental, inescapable problem with step functions
> in isosurfaces.? Perhaps his solution is simply a clever use of the
> max_gradient at 50 that none of us thought of before.? Will
> experiment after I put the baby to sleep.
I understand that...and I would like to see some experiments using the
object pattern with this technique. He seems to have overlooked it...
However, if it is a problem with normal calculation(or self shadowing,
another possibility), there might be a better way to solve it than using
an extremely high gradient. If someone takes a closer look at what goes
wrong and why his code gives a better image, they might find a faster
rendering compromise.
--
Christopher James Huff
Personal: chr### [at] mac com, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tag povray org, http://tag.povray.org/
<><
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