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Le 18-04-01 à 11:30, Bald Eagle a écrit :
> "944291641" <944### [at] qq com> wrote:
>
>> Recently I have encounter another question , could you give me a hand?
>>
>> I build a scene which contains some trees, and I want calculate the area of the
>> sunlit leaf and the shaded leaf. For that I am a Pov-Ray beginner, I don't know
>> if there is any functions that can achieve this goal.
>
>
>
> Do you need to calculate that for ALL the leaves in a scene, or just one?
>
> You could probably render a single leaf, with a fairly artificial setup that
> gives a certain color of final rendered pixel for lit, a certain color for
> unlit, and a distinct background color (I'd go with transparent).
>
> Then you could scan and count the pixels of the different colors.
>
> Sorta like this:
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.58cfc0cf857600e8c437ac910%40news.povray.org%3E/?mtop=416151
>
>
> POV-Ray has internal processes that count ray-object intersections, and there is
> also trace () and eval_pigment ().
>
> Perhaps there's a way to determine how much total leaf area there is, how much
> is directly lit, and then subtract lit from total.
>
>
eval_pigment() return the raw value of the pigment at a specific point.
It can't take illumination into account.
To tell is some point on some object is lit or not, you need to take
that onject, bind it with every other objects in your scene, trace from
the light's location toward the object.
Now, you need to see if the trace hit your object, or some other
intervening object. That mean comparing the result returned by the
trace() with the actual location of your object.
Any transparent object can intercept the trace, so, the fully
transparent objects need to be removed.
If you have an object that is transparent in only some of it's part, or
is partially transparent due to a filtering or transmiting texture,
then, you need to identify that object and do another trace from just
past that object onward IF you hit a transparent part.
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