On 2025-11-26 10:53 (-4), Bald Eagle wrote:
> 
> I was also trying to re-code an old scene where I was initially trying to
> replicate source-code methods in SDL, and I believe I was trying to do what
> Cousin Ricky was doing - which is trying to use a scalar value to create a
> "normal".
> 
> A surface normal is, by definition, a vector perpendicular to the surface at
> that point.   It's a vector, not a scalar, so using the scalar result from an
> SDL function as a normal really doesn't make any sense.

So far as I understand, the scalar is an offset from the surface, and as
such, a vector perpendicular to the unperturbed surface is implied.
POV-Ray then computes a normal vector by comparing adjacent
perturbations, "adjacent" being defined by the 'accuracy' attribute.

I haven't examined the source code, so I could be wrong, but I would
expect "adjacent" samples to be free from bias, at least from opposite
directions.

> I believe one would need to use a spline function, a pigment function, or some
> other vector-valued function to properly use a function {} in a normal statement
> to get meaningful if not proper results.

This actually sounds like an excellent way to *introduce* directional
bias if you're not careful with the function.  ISTR some of POV-Ray's
built-in normals already have that problem.

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