Warp napsal(a):
> Jan Dvorak <jan### [at] centrumcz> wrote:
>>>   double_illuminate is not realistic. It doesn't correspond to any
>>> physical phenomenon.
>>>
>> It does correspond to any surface that is thin enough to be translucent 
>> but thick enough not to be transparent.
> 
>   No, it doesn't. Just take any material you want and compare its
> illumination on the side facing the light and on the opposite side.
> The illumination is totally different. With double_illuminate the
> illumination on both sides will be *identical*. This corresponds to
> nothing in nature.
> 
>   The only reason why double_illuminate exists in povray is because it's
> so laughably easy to implement (it's a 1-liner: 1 single 'if' statement;
> or more precisely, one additional condition in an existing 'if' statement),
> and it can be used in certain situations to eg. alleviate some rendering
> artifacts, as well as other purposes. It's not even intended to be a
> physically accurate feature.
> 
>> A good example is a paper 
> 
>   Emulating the illumination on the backside of a paper in a physically
> accurate way would be quite laborious and slow.
> 
>   double_illuminate might be a somewhat acceptable approximation in some
> situations, assuming you are not seeing both sides at the same time (in
> which case it would be very unrealistic).
> 
Read the "However, I do see a bit of unrealism" part.

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