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On Sat, 12 Jun 1999 16:57:15 -0500, Mike <Ama### [at] aol com> wrote:
>> Regarding your proposed patch - if it is fast, that would be nice. POV
>> currently subdivides bicubic patches. It has an option to subdivide only
>> as needed (practically 'direct rendering') but this is much slower than
>> pre-computed subdivision. If you have a technique that is fast, that
>> would be great.
>
>I should mention that I will be trying to implement code written by Sean Graves
>in 1990, so I really wouldn't be writing anything original. It uses the
>newtonian method, which I hear is pretty fast but can have problems with
>returning wrong intersections. If I can get it to work, then I may be able to
>improve it by including bezier clipping and bounding volume heirarchy. This is
>my first attempt at an actually useful patch, so I don't know yet if it's
>beyond my abilities.
>
>The main impulse for doing this is that I find the u and v steps annoying in
>the current implementation. No matter what the screen resolution, POV-Ray will
>always use the same number of subdivisions. The results are not only slow, but
>rather jagged around the edges with some of the scenes that I've tried
>rendering with large numbers of bicubic patches. It seemed to me that to alter
>the code to tesselate down to a pixel in size would make rendering unbearable.
The superpatch and the isosurface patch have code for a "type 2"
rendering method for bicubics that takes an accuracty parameter
instead of u_steps and v_steps. It also has support for rational
bicubics and trimmed bezier splines.. You might want to look at that
and see how close it gets to NURBS before you set off across strange
new territory on your own.
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