"crackle metric infinite"
replaces (dx^n + dy^n + dz^n)^(1/n) with max(dx,dy,dz)

"crackle tumbled"
randomly rotates, for each nucleus, the coordinate axes on which
dx,dy,dz are computed.  (has no effect on metric 2.)  without this, the
`grains' all line up alike, which is generally not how real minerals
behave.


i'll go be quiet now.

-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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Anton Sherwood wrote:
> 
> "crackle metric infinite"
> replaces (dx^n + dy^n + dz^n)^(1/n) with max(dx,dy,dz)
> 
> "crackle tumbled"
> randomly rotates, for each nucleus, the coordinate axes on which
> dx,dy,dz are computed.  (has no effect on metric 2.)  without this, the
> `grains' all line up alike, which is generally not how real minerals
> behave.
> 
> i'll go be quiet now.
> 

Hmm, sounds interesting, do you have some sample pictures? 'infinite'
would also be much faster BTW.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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> > Anton Sherwood wrote:
> > > "crackle metric infinite"
> > > replaces (dx^n + dy^n + dz^n)^(1/n) with max(dx,dy,dz)
> > >
> > > "crackle tumbled"
> > > randomly rotates, for each nucleus, the coordinate axes on which
> > > dx,dy,dz are computed.  (has no effect on metric 2.) ...

> Christoph Hormann wrote:
> > Hmm, sounds interesting, do you have some sample pictures?

Anton Sherwood wrote:
> [some urls]


Scratch that (sorry i can't cancel) - see
	http://ogre.nu/tumble/


> (The distribution of nuclei is likely wrong.)

-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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These all look really good, will you release a patch with that extension?

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Christoph Hormann wrote:
> These all look really good, will you release a patch with that
> extension?

Do I look like a programmer? ;)  Those are fakes.

Oops, maybe I shouldn't have said that.
In an old sf story, some scientists are shown a top-secret movie of an
antigravity experiment, and told that the movie is the only record
surviving after an explosion killed everyone in the project.  The
scientists go away and "re"invent antigravity.  Afterward, it is
revealed that the movie was a fake.

-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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Anton Sherwood wrote:
> 
> Do I look like a programmer? ;)  Those are fakes.

Ohhh!

And how did you do them?

I really wonder if the actual implementation would look the same...  

> 
> Oops, maybe I shouldn't have said that.
> In an old sf story, some scientists are shown a top-secret movie of an
> antigravity experiment, and told that the movie is the only record
> surviving after an explosion killed everyone in the project.  The
> scientists go away and "re"invent antigravity.  Afterward, it is
> revealed that the movie was a fake.
> 

:-)

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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On Wed, 09 May 2001 23:37:51 -0700, Anton Sherwood wrote:
>"crackle metric infinite"
>replaces (dx^n + dy^n + dz^n)^(1/n) with max(dx,dy,dz)

This one's pretty easy, and certainly nicer than the current solution of
just setting the metric really high and waiting.

>"crackle tumbled"
>randomly rotates, for each nucleus, the coordinate axes on which
>dx,dy,dz are computed.  (has no effect on metric 2.)  without this, the
>`grains' all line up alike, which is generally not how real minerals
>behave.

Do you happen to have a formula that will translate a random vector in the
unit cube between <0,0,0> and <1,1,1> into a set of basis vectors and give
uniform coverage of the space of all possible basis vectors?  I seem to have
left mine in my other coat.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end 
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}

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Ron Parker wrote:
> Do you happen to have a formula that will translate a random vector
> in the unit cube between <0,0,0> and <1,1,1> into a set of basis
> vectors and give uniform coverage of the space of all possible
> basis vectors?  I seem to have left mine in my other coat.

<g>

I'll think about it some more, and come up with a dumb idea.
Then I'll ask sci.math.

It doesn't have to be purely uniform, though;
rotate <90*rand(),90*rand(),90*rand()> might be good enough.

-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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> Ron Parker wrote:
> > Do you happen to have a formula that will translate a random vector
> > in the unit cube between <0,0,0> and <1,1,1> into a set of basis
> > vectors and give uniform coverage of the space of all possible
> > basis vectors?  I seem to have left mine in my other coat.

Anton Sherwood wrote:
> I'll think about it some more, and come up with a dumb idea.
> Then I'll ask sci.math.

Got it.  (I'll call your random vector <rx,ry,rz>)

theta = rx*2*pi;
phi = acos(2*ry-1);
v0 = sphere_to_xyz(theta,phi); /* uniform by Archimedean theorem */
vtemp = one of the axis vectors, 
	corresponding to the smallest component of v0;
v1 = vaxis_rotate(vtemp,v0,rz*360);
v2 = vcross(v0,v1);
v0 = vcross(v1,v2);

v0,v1,v2 are the new basis.

(The rigmarole with vtemp is to get it down to three rands;
it's more obvious with four.)

-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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> > Do I look like a programmer? ;)  Those are fakes.

Christoph Hormann wrote:
> Ohhh!
> And how did you do them?

Mesh pyramids, randomly placed, variously pigmented: gradient z
for "color", slope for "normal", rgb <rand()...> for "solid".
finish { ambient 1 }
camera { orthographic }


> I really wonder if the actual implementation would look the same...

I'd expect some difference because I only rotated the pyramids on z --
and because I've no idea how crackle places the nuclei.


... Meanwhile, another idea: if (dx,dy,dz) were replaced with
(dx+dy,dx+dz,dy+dz), the `crystal' would be a rhombic dodecahedron. 
Maybe I can get Grimbert interested. ;)

Is there a "So You Want To Patch Povray" faq somewhere?


-- 
Anton Sherwood  --  br0### [at] p0b0xcom  --  http://ogre.nu/

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