CAD-Andi nous apporta ses lumieres en ce 2008/01/08 23:11:
> Hi!
> 
> I'm experimenting with POVRay to simulate a simple physics-lab setup involving
> the following:
> 
> A spot light
> A Mirror Surface (does not need to be visible, just must perfectly reflect the
> light.)
> Some shadow generating objects before and after the mirror (invisible to the
> camera too)
> A semi-transparent Screen that catches and displays the reflected photons.
> 
> I've accomplished this task already by using "double_illuminate" for the
> screen., but I'm struggling with optimizing the render time.
> I understand that photons take their time to be calculated. But for a simple
> setup like
> this I hope I can keep the render time under halve a minute for a 600x800 image.
> Can someone give me some hands on tipps about best global settings and about how
> useful
> commands like "autostop" and other options like "adc_bailout" could be?
> Maybe with a little example script, optimized for fast calculation, showing a
> sharp and crisp projection of light reflected by a rectangular mirror against a
> screen. I don't need fancy blending and anti-alias. Speed is what I seek :-) ...
> Thanks in advance!!
> 
> PS: I think POVRay is the cooles thing since melted cheese!
> 
> Andi
> 
> 
What exactly do you see?
You may be able to go by without using photons. If you only see the screen and 
not the mirror nor the objects that cast the shadows, you can use some tricks.
Use an orthographic camera with a projection plane equivalent to the screen.
Replace the mirror by a white surface.
Have all objects be completely black. pigment{rgb 0}
Keep the spotlight as it is.

The objects before the surface will cast shadows on the plane.
The objects after the plane will hide it and show as black silouetes.
Net result: only use direct view and only test for shadow.

Autostop is usefull if you have objects that don't fill ther bounding box, not 
usefull in your case.
adc_bailout is for multiple reflections and transmission. It limit the number of 
surfaces treated when the surface contribution drop under a given treshold 
value: not your case.

-- 
Alain
-------------------------------------------------
Congregationalist: Shit that happens to one person is just as good as shit that 
happens to another.

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