"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:
> >
> > First, I was surprised that your constructed DIRT function works at all. Z's
> > instead of y's there? But it does work! Substituting y for z *also* works:
> >        function(x,y){select(PigM(x,1-y,0).blue,0,0,PigM(x,1-y,0).blue)}
>
> You can of course put anything you want in those "slots".   It's a function.
> When you render an image and you are evaluating a pigment pattern, then you
> have the ability to sample the x, y, and z values at the place where the
> ray-object intersection takes place.  But there sure isn't a requirement
> to invoke any function in that order, or even using those values at all.
> Using z instead of y just switches the plane in which that function is
> evaluated.
>

But in the case of a function from a (flat) image_map, isn't the 'plane' just
x/y?

My understanding (from the docs) is that a function takes only a 'slice' of a
pattern in the x/y plane, by definition. Granted that most patterns are 3-D and
that even an image_map extends infinitely into z, I thought that the function
would need x and y (not z) as its arguments because of that 'slice'. In other
words, z is usually not used at all (and/or has no real meaning for a flat
image_map.) But since Leroy's function works as-is and uses z... there is
obviously still something fundamental that I'm not grasping about function
arguments and what they mean.

:-[

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