On 1/28/22 17:01, Bald Eagle wrote:
> I would tend to start from scratch, and just cancel all of that extra stuff and
> see what happens. Maybe it might explain why they decided to do all of that.

A look at the basics is good advice.

I did get to commenting all the fix bugfix code and got results more in 
line with what I originally expected. As of this morning I'm leaning 
toward bringing out various treatments as user controllable variations. 
  I can see physical reasons for a few depending upon the actual surface 
and the non-perturbed rays. Given that glassy result is probably useful 
would likely keep it as perhaps an expanded option. Suppose keeping the 
current behavior as an option a good idea too.

Likely the povr default would be no bugfix / adjustments at all as I 
think it the result most would expect. I also like the look of it over 
the current for usual use 'micro' micro results.


This morning been looking at the refracted side of things.

A simplified view:
------------------

Where the perturbed normal is running along with (inverted with respect 
to the incoming ray) the perturbed normal is inverted and assigned a 
local normal for color calculations.

Where the refracted ray ends in internal reflection the perturbed normal 
is used and the compute reflection bugfix gets used as with any other 
reflection.

Where the refracted ray continues creating a new refracted ray the, 
always pointing back toward the ray, normals - the potentially inverted 
local normals - get used

So! The refraction behavior isn't really aligned with reflection 
behavior at any given surface intersection where the perturbed normals 
point in opposition to the refracted/reflected rays. In the case of 
reflections sometimes if in enough conflict with the raw normal.

A realization for me is, while it's possible in some cases to prevent 
the inversion of perturbed normals with respect to the major surface 
direction with some patterns, it is not possible to do in general 
because there are really two kinds of perturbed normal inversion. One 
with respect to the surface itself, and another with respect to the rays 
involved.

That said, a common to all normal patterns, perturbed normal inversion 
option for where the perturbed normal points away from the raw normal 
might be of use... This would immediately get us to a state where there 
are only the inversions with respect to involved rays issues.

---
I guess a take away here for POV-Ray proper is where you are using 
reflection or refraction, keep the normal bump size smallish (<0.5). 
Even so, where rays nearly tangent to the surface, ANY normal 
perturbations will invert somewhat at those locations with respect to 
incoming rays.

I suppose what can be said generally is the moment we start to fake 
surfaces / shapes to some degree or another, the reflections and 
refraction treatments necessarily get somewhat heuristic.

Bill P.

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