William F Pokorny <ano### [at] anonymousorg> wrote:

> I created quilted test cases and reviewed the shipped demo scenes. A
> number of other issues popped out. One of which is the 'true normal'
> results do not match what our documentation shows for quilted normals.

Perhaps I'm wrong or misreading something, but it doesn't appear that the
documentation properly describes the pattern.

http://wiki.povray.org/content/Reference:Quilted_Pattern

Just looking at the last image,
"A control value of 1 at both ends will give an "s" shaped curve, resulting in a
softer, more rounded edge."
yet the solid line is the s-shaped curve, and it says for that c1 = 0.

After skimming through the source code in patterns and normals, the basic
formula used to generate the curve seems an awful lot like a specialized form of
bicubic spline with c0 and c1 influencing the internal two control points...

but it's ... bizarrely different.
And I can't reproduce the curves and s-shape reliably.
And I don't know why they don't use a function based on 2*x, or use mod(), ...

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