Christoph Hormann wrote:
> David Burnett wrote:
>> of the function, so for the example images its
>> equivalent to...
>>
>> f_crackle(x*f_bozo(x,y,z), y*f_bozo(x,y,z), z*f_bozo(x,y,z))
>>
>> [...]
> 
> 
> I don't think this is a very useful interpretation of a function as a 
> warp, even if it leads to interesting results in this case.  The pattern 
> gets scaled by the value of the function - to imagine how this 
> influences a pattern seems quite difficult to me.
 > I think the most intuitive interpretation of a float function as a
 > warp  would be the gradient - like it is used in the type 1 displace 
 >warp.
 >

Well I'd said is about as obvious as a 1 octave turbulence warp :-)
which I guess it is when it comes down to it. The direction of
movement isn't random, it's the same direction as the current
point is from <0,0,0> but the distance traveled past the current
point is the result of the function.

I choose multiplication as I'd already used it in
planetGenesis a little Java 'heightfield' generator
I occasionally attempt to program and got some nice
results, and I wanted to see how they would look as
isosurfaces.

Anyway, now I've put the source out there, give it
a try, you'll get some fun results, and maybe grow
to like it.

Dave





I haven't looked at that


> Christoph
>

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Is that true displacement? Because that's the one thing I miss in POV.

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Roberto A. wrote:
> Is that true displacement? Because that's the one thing I miss in POV.
> 

Not really.
It's an isosurface using the noise subtracted, from f_r(),
which is as close to displacement that POV gets.

I supposed you could argue its a limited version of
displacement, you need a function to derive the original
shape, rather than being able to displace anything.

Dave

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In article <3f8af3ec$1@news.povray.org>,
 David Burnett <var### [at] ntlworldcom> wrote:

> It's an isosurface using the noise subtracted, from f_r(),
> which is as close to displacement that POV gets.

I'd say true displacement is as close to true displacement as POV gets...
Combining functions in this way isn't really displacement, but you can 
do real displacement by modifying the coordinates given to the function. 
Common examples of this are scaling by dividing the coordinates or 
translation by subtraction. Just use something like:

originalFn(x - xDispFn(x, y, z),
           y - yDispFn(x, y, z),
           z - zDispFn(x, y, z)
)

Warping a function also qualifies as true displacement...
http://news.povray.org/povray.binaries.images/11612/

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff wrote:
> In article <3f8af3ec$1@news.povray.org>,
>  David Burnett <var### [at] ntlworldcom> wrote:
> 
> 
>>It's an isosurface using the noise subtracted, from f_r(),
>>which is as close to displacement that POV gets.
> 
> 
> I'd say true displacement is as close to true displacement as POV gets... 
> Warping a function also qualifies as true displacement...


Hmmmm, I'm personally not sure *I'd* count anything done in a
isofunction true displacement (you're just changing the function
or the function input so for me its still the 'original' shape)
but do I see what you're getting at.

Dave

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David Burnett wrote:
> [...]
> 
> Hmmmm, I'm personally not sure *I'd* count anything done in a
> isofunction true displacement

And i am not sure whether you can clearly define what you understand as 
'true displacement'.  As Chris Huff said you can't really get much 
closer to true displacement than with isosurfaces.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 2 Sep. 2003 _____./\/^>_*_<^\/\.______

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Christoph Hormann wrote:
> David Burnett wrote:
> 
>> [...]
>>
>> Hmmmm, I'm personally not sure *I'd* count anything done in a
>> isofunction true displacement
> 
> 
> And i am not sure whether you can clearly define what you understand as 
> 'true displacement'.  

I mean displacement in the renderman displacement shader sense which
is what Roberto was asking about, hence in this case 'true 
displacement'. A function (in this case a shader)
applied to an object, sphere, mesh, plane etc which change its
geometry.

As I stated IMHO isosurfaces are not displacement as there is no 
original object expect the one created by the function. It doesn't 
matter what you do within that function what you get is still the 
'original' object not a displaced one.

Picky, oh yes.

Dave.

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On Wed, 15 Oct 2003 18:56:23 +0100, David Burnett <var### [at] ntlworldcom> wrote:
> I mean displacement in the renderman displacement shader sense which
> is what Roberto was asking about, hence in this case 'true 
> displacement'. A function (in this case a shader)
> applied to an object, sphere, mesh, plane etc which change its
> geometry.

Is that displacement on object/sphere/plane/mesh or is is only on meshes (if
you know what I mean in my question)?

> As I stated IMHO isosurfaces are not displacement as there is no 
> original object expect the one created by the function. It doesn't 
> matter what you do within that function what you get is still the 
> 'original' object not a displaced one.

Thinking that way displacement of mesh surface is only new mesh (even if it is
calculated on the fly). You can work with displacement on
functions/isosurfaces were efficient way if you have tools like:
http://www-public.tu-bs.de/~y0013390/pov/ic/docu02.html#Displace

ABX

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David Burnett wrote:
> 
> I mean displacement in the renderman displacement shader sense which
> is what Roberto was asking about, hence in this case 'true 
> displacement'. 

Renderman (at least the PRMan implementation) is not a raytracer.

> A function (in this case a shader)
> applied to an object, sphere, mesh, plane etc which change its
> geometry.
> 
> As I stated IMHO isosurfaces are not displacement as there is no 
> original object expect the one created by the function. It doesn't 
> matter what you do within that function what you get is still the 
> 'original' object not a displaced one.
> 
> Picky, oh yes.

No, it's simply wrong.  Isosurfaces are just a more general feature than 
a displacement shader.  Displacement there is limited to mesh 
geomentries since - as mentioned above - it has to work for a scanline 
renderer.  You can model a shape as an isosurface function and then 
displace it - just like with a shader.  The only difference is that with 
isosurfaces you can also do much more.

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 2 Sep. 2003 _____./\/^>_*_<^\/\.______

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> > I mean displacement in the renderman displacement shader sense which
> > is what Roberto was asking about, hence in this case 'true
> > displacement'. A function (in this case a shader)
> > applied to an object, sphere, mesh, plane etc which change its
> > geometry.
>
> Is that displacement on object/sphere/plane/mesh or is is only on meshes
(if
> you know what I mean in my question)?

Displacement on Renderman can be applied to any primitive that takes
shaders, with the exception of points and curves. That means meshes,
subsurface subdivision meshes, spheres, cones, etc.

Regards,

Roberto

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