tasuki nous apporta ses lumieres en ce 2007/09/13 12:10:
> Hello,
> 
> as the subject hints, I have a thin object lighted by an area light. The
> shadows look just awful: If I use a small number of lights in the area
> light (less than ten), the shadow is not smooth enough. If I use six or
> more, I always get weird holes in the shadow (this is true even when I use
> 100 lights (with NO adaptive area lights, as adaptive lights obviously
> cause even bigger holes in the shadow)).
> 
> Well, I hope I explained it clearly enough. :)
> Surely, someone must have noticed this earlier than me and found a
> solution...
> 
> Thanks for your help!
> tasuki
> 
> 
> 
This is due to the fact that area_light are composed of several point_lights 
disposed in a regular array. Some shadowed points may be in view of all of those 
points.
The use of jitter can help hide this, as for each points tested, the location of 
each element is slightly shifted randomly from it's original position for the 
shadow evaluation. This random noise is normaly unnoticeable.

In a personal test with a 9*9 area_light 5 by 5 units, 5 units above a rotating 
cylinder 0.03 unit whide and 3 units over a while plane, jitter on, adaptive 1 
or even 0.
I don't see any banding, no hole and no dark spot. In fact, the shadow is so 
diffuse that it's almost invisible. I need to place another cylinder on the 
plane to show me where the shadow's center should be.
Even going down to a 3 by 3 array and it's still OK.
Without jitter, the result is horrible.
A similar setup would give a similar result in real life.

-- 
Alain
-------------------------------------------------
To err is human, to forgive is not our policy.

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