Re: [Algorithms] Bicubic normals for a bicubic world

[John S. <jse...@ho...>]

Well, I'm trying to avoid five cross products (one per point generated -
forty multiplies and twenty subtracts total) at every patch subdivision, not
to mention that I don't have the Bezier control points once I start
subdividing (using central diffrencing).

I just want an approximation better than linear, so the threshold value the
normals are compared against to determine backfaces can be as small as
possible.

A technique to approximate the normals with a bicubic is supposedly
described the the Proceedings of SIGGRAPH '82, but since that's so old, I
can't seem to get it anywhere.

Somehow, I think finding the Holy Grail would be easier... ;-)

Thanks again.

John Sensebe
jse...@ho...
Quantum mechanics is God's way of ensuring that we never really know what's
going on.

Check out http://members.home.com/jsensebe to see prophecies for the coming
Millennium!


----- Original Message -----
From: "Akbar A." <sye...@ea...>
To: <gda...@li...>
Sent: Thursday, August 03, 2000 8:21 PM
Subject: RE: [Algorithms] Bicubic normals for a bicubic world


> hello john,
> expensive?
>
> calculate the tangent vectors, compute cross products at each corner of
> patch.
>