RE: [Algorithms] Bicubic normals for a bicubic world
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From: Akbar A. <sye...@ea...> - 2000-08-04 03:19:01
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hmm, if you know what your going to be subdividing too, what about a precalculate lookup method for the normal data? then once you hit a certain subdivision level, you just look up the normal in the precalculate array? i guess you have to make one of those trade off decisions. lots of memory versus cpu cycles in the real time sector. isn't it acm's job to keep track of the siggraph papers? peace. akbar A. "We want technology for the sake of the story, not for its own sake. When you look back, say 10 years from now, current technology will seem quaint" Pixars' Edwin Catmull. -----Original Message----- From: gda...@li... [mailto:gda...@li...]On Behalf Of John Sensebe Sent: Thursday, August 03, 2000 9:09 PM To: gda...@li... Subject: Re: [Algorithms] Bicubic normals for a bicubic world 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. > _______________________________________________ GDAlgorithms-list mailing list GDA...@li... http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list |