On Sun, 4 Aug 2002 17:04:54 +0200, Rune wrote:
> Ron Parker wrote:
>> You missed the d/du and d/dv of the surface,
>> which are available in SL but not anywhere in POV.
> 
> I don't even know what that means or what it would be used for when
> creating "shaders"... :)

SL is the Renderman Shading Language.  The d/du and d/dv are my attempts
to represent the partial derivatives of the location of the surface with
respect to the surface's U and V coordinates.  d/du and d/dv are used in
antialiasing, to make decisions about how intricate the texture should be
at a given point.  For example, if your shader is a checkerboard, but the
rate of change at the location you're sampling is so high it'd have multiple
squares in the same pixel, you're better off returning an average of the 
two base colors.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end 
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}

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