Hi,

>   Your "true" area light is not a true area light. It's a grid of point
> lights, which is a completely different thing.

I know, I just called it truAreaLight as a name. I realise that a "true"
area light is a very complex thing to simulate in a raytracer, and that
you'd probably have to implement some kind of Monte Carlo engine to do
forwards-raytracing or something equally nasty. My grid of point lights was
just an implementation of what I thought the Povray area light was under the
hood.

>   There *is* a major difference between area_lights and grids of point
> lights: The area_light calculations are done *only* for shadow testing.
> Nothing else. For any other purpose an area_light is a point light and
> nothing more. (I'm not saying that this is a good thing; I'm just stating
> the fact.)
>   (Ok, photons is another place where area_light makes a difference if
> configured to do so, but that's another different issue.)

As I have subsequently found out, and that nullifies Test One in my article.
I still don't think it's right, but it at least explains why I got the
results I did.

>   By the way, I don't like your attitude at pointing at area_light
"defects"
> which are simply caused because you used an adaptive value which was too
low
> or too low dimensions. The documentation is quite clear about this: It
> explains in full detail what does 'adaptive' do and what happens if it's
too
> low.
>   Since that is an artefact which is to be expected from a too low
adaptive
> value and this is clearly explained in the documentation along with a
simple
> solution (ie. use a larger adaptive value and if that's not enough,
increase
> the dimensions of the area light), it's unfair that you speak of it as if
it
> was a defect.

As I just said in my reply to Jamie, "Shadows are only a side effect of the
absence of light; the soft shadows should be a side effect of the fact that
an arealights illumination doesn't come from a point". I believe that the
very fact that there is a disparity between the illumination model that
Povray uses for its arealight and the model it uses to calculate shadows for
the area light totallys break any kind of intuitive concept about how
illumination works. Povray arealights were designed to give soft shadows; I
believe that the illumination that arealights give off was only a distant
secondary concern. That is why I think that Povray arealights are a cheap
hack; it is the special *illumination* property of an arealight that should
be what makes it different from point light sources - the soft shadows
should just be a natural side effect of the used defined properties for the
arealight's source.

I consider the fact that Povray works the exact opposite way to this, in
which the user sets up properties to affect how the *shadows* work (seeing
as no setting apart from colour and falloff and so on will affect the
illumination), to be a defect. Therefore, seeing as adaptive is just an
extra step in this process, it is part of the defect. Do you understand what
I mean?

I'm sorry if I sound so negative, but I just think that arealights in Povray
are just plain *wrong*. It would be great if they could be updated for 4.0
;)


John

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