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Xiaobin Wu 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).
>
>
> I was pondering about the usual scenarios that users specify the normals
> and apply the subdivision. Do they want part smooth/part flat shading,
> or normal effect (bump mapping, etc) or maybe even crease controls?
In POV-Ray the way to get interpolated normal vectors (or 'smooth
shading' if you want so) is to specify the normals, This offers more
control than simply specifying if an edge is sharp or smooth. If there
is a mesh with some smooth triangles and some not the most convenient
approach would be to only subdivide the smooth ones (which of course
requires special handling of edges between smooth and flat triangles).
> Before I can get a sense of practical demand, I decided not to use the
> supplied normal for anything. But this is really open for options. After
> I see more examples that requires normal control, I would love to implement
> that in.
>
> About the computations, determining the neighboring triangles is needed
> for subdivision. So it is a must anyways.
That depends on the method used. Most methods for doing on-the-fly
subdivision (which is an interesting feature for a raytracer BTW) do not
use the neighbouring triangles.
>>- i can't find a reason why it should only work for mesh2 and not mesh.
>
> There is really no reason that it would not work with mesh. But often
> enough, mesh objects are built without precisely matching vertices. The
> subdivision will result in surfaces with gaps (remember shrinking
> boundaries).
You will need an adjustable threshold to determine if two vectors are
considered identical or not.
Christoph
--
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 01 May. 2004 _____./\/^>_*_<^\/\.______
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