> 
> I've implemented this in my own raytracer, the neighbouring triangles are
> required to satisfy boundary conditions for subdivision, unless these
> conditions are specified manually (which is rather awkward).  The
> implementation really is quite interesting, if you are interested check
> out the paper:
> http://www.seanet.com/~myandper/abstract/eg03.htm
> 
> Andrew

Sorry, A more relevant paper is:
http://portal.acm.org/citation.cfm?id=344829&dl=ACM&coll=portal

Although both these are highly relevant to a raytracing implementation of
subdivision and displacement mapping.

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Some improvements have been made to
the blender export script for povray,
so now you can export mesh for pov-sub too,
and test  complex material mixing:

http://jmsoler.free.fr/util/blenderfile/povanim_patch4.htm

Regards.

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This is wonderful. Thanks.

<nomail@nomail> wrote in message
news:web.40a517e4156ced50ba91e9880@news.povray.org...
> Some improvements have been made to
> the blender export script for povray,
> so now you can export mesh for pov-sub too,
> and test  complex material mixing:
>
> http://jmsoler.free.fr/util/blenderfile/povanim_patch4.htm
>
> Regards.
>
>

Post a reply to this message

"John VanSickle" <evi### [at] hotmailcom> wrote in message
news:40A40E63.5DDEA331@hotmail.com...
> Christoph Hormann wrote:
> >
> > - you seem to discard any normal vectors specified for the mesh - this
> > might often not be what the user wants and more important using the
> > normal vectors could save you quite some computations (i.e. determining
> > the neighbouring triangles).
>
> And determining if the edge between two triangles is sharp or smooth,
> which is very important for subdivision surfaces.

Crease edges are important. I am considering to use the Pixar's semi-crease
rule.
So you can specify an integer on an edge which indicates "how" smooth
it is. 0 means smooth, infinity means sharp and integers in between will
create semi-sharp ridges. The syntax will look like

  crease_edge_list {
    v1 v2 crs_value
    ...
  }

Reference: Subdivision surfaces in character animation, by Tony DeRose, etc.

I found this practically essential and relatively easy to use. Also this way
the
manual normals can be saved for bump mapping purposes. (i.e. smooth
geometry with artrificial normals on it)

> Mesh2 allows you to explicitly specify that two triangles share their
> corner vertices (instead of having different vertices that happen to be
> identical).
Exactly.


Xiaobin

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"Warp" <war### [at] tagpovrayorg> wrote in message
>   Note also that two smooth triangles might not share the same normal
> vectors in their shared vertices. That is, the triangles are smooth, but
> their common edge has a sharp change in lighting (which is often a useful
> feature).

I have this in mind. Thanks. I called it bump mapping or artificial normals,
which shouldn't affect the shape.

I remember one of the nicest example is a coin modeled by a simple
cylinder but with artificial normals on its sides. Since its sihouette is
always from the cylinder, you can never tell its sides are actually flat!

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In article <40a593f3@news.povray.org>, "Xiaobin Wu" <xwu### [at] ciseufledu> 
wrote:

> "Warp" <war### [at] tagpovrayorg> wrote in message
> >   Note also that two smooth triangles might not share the same normal
> > vectors in their shared vertices. That is, the triangles are smooth, but
> > their common edge has a sharp change in lighting (which is often a useful
> > feature).
> 
> I have this in mind. Thanks. I called it bump mapping or artificial normals,
> which shouldn't affect the shape.

I don't think you quite understood. For example, think of a deformed 
box. It has edges that should not be smoothed out, but which are actual 
geometry, not faked by tweaking the normals.


> I remember one of the nicest example is a coin modeled by a simple
> cylinder but with artificial normals on its sides. Since its sihouette is
> always from the cylinder, you can never tell its sides are actually flat!

I'm not sure what this has to do with subdivision...normal perturbation 
in POV is specified as part of the texture. Some objects will return 
"false" normals...smooth triangles, smoothed height fields, etc.

-- 
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" <cja### [at] earthlinknet> wrote in message
news:cjameshuff-2CC397.15040617052004@news.povray.org...
> In article <40a593f3@news.povray.org>, "Xiaobin Wu" <xwu### [at] ciseufledu>
> wrote:
>
>
> I don't think you quite understood. For example, think of a deformed
> box. It has edges that should not be smoothed out, but which are actual
> geometry, not faked by tweaking the normals.

OK. Here are the two cases:
   1. Smooth geometry, non-smooth normals.   (Bump mapping)
   2. Non-smooth geometry, non-smooth normals. (sharp creases)

Now with another look at warp's post, I am not that sure which case he was
referring to.
It could well be either one.

If only the second case is concerned,  one could automatically determine the
crease edge
from the normal directions (which is simple). But I am ambitious to support
both cases, as well as "semi-sharp" creases. They seem useful to me in
practice.

Xiaobin

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