Re: approximation to pow(n,x)?

And in that spirit I would recommend Schlick's BDRF papers. Besides
using half-vector and deriving a really good looking physically-based
model, Schlick has derived some very nice approximations based on
division of polynomials instead of pow() function. That approach is
faster, doesn't suffer from that much precision issues, and has
another nice property that parameters can be made to fit the 0..1
domain. I consider that a big plus, since it allows for easy storing
of the parameter in a texture.

Such approximations are very useful even for other applications, not
just specular lighting. (Which we still don't have any evidence is
what OP needs. ;) )

Alen

Wednesday, November 4, 2009, 9:00:19 PM, you wrote:

> The difference is in the shape of specular highlights. Where Phong
> specular highlights at grazing angles are streched out moon shapes,
> the Blinn half-angle highlights retain a more circular shape. Real
> world photos of specular surfaces at grazing angles more closely
> resemble Blinn shapes than Phong, plus the Blinn model has some good
> physical reasoning behind it to do with reflection from distributions
> of microfacets.

> http://img22.imageshack.us/img22/7/blinn.jpg
> http://img526.imageshack.us/img526/758/phong.jpg

> - Robin Green.



> On Wed, Nov 4, 2009 at 10:14 AM, Jeff Russell <[email protected]> wrote:
>> Not to derail the conversation, but I've never really understood why half
>> vectors are preferable to an actual reflection vector, either in terms of
>> efficiency or realism. I've always just used reflection, am I missing
>> something?

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-- 
Best regards,
 Alen                            mailto:[email protected]


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