Tom York nous apporta ses lumieres en ce 2007/06/30 20:34:
> I implemented a basic sort of ambient occlusion using the MegaPOV 1.2.1
> source as a base. The idea behind ambient occlusion is outlined here, if
> you've not heard of it before:
> 
> http://www-viz.tamu.edu/students/bmoyer/617/ambocc/
> 
> The example on that page pretty much sums up my use case: a shader that will
> produce an occlusion image that I can layer over a direct illumination pass
> to suggest more realistic shading. There are alternative ways in povray to
> get the ambient occlusion effect, and alternative ways to fulfill the use
> case as well, but I liked the simplicity of the ambient occlusion idea, and
> after experimenting with a method based on the proximity pattern I decided
> that source modification was probably the cleanest and fastest route to go.
> 
> At the moment the effect samples entire hemispheres (I thieved the
> hemispherical sample set that standard radiosity uses, I'm afraid), so you
> need a lot of samples to reduce the noise. Because the sampling surface is
> so extensive, objects also react quite strongly to each other and the
> occlusion effect is very visible. Narrowing the sampling surface would
> concentrate the effect (and require fewer samples to reach the same noise
> level). I've heard (here?) that altering the sampling surface can alter the
> perception of scale the effect produces.
> 
> The attached image shows a simple scene using 128 AO samples, consisting of
> a sphere and a few cylinders, with some cylinders CSG differenced. It took
> 22 minutes to render on a laptop with a Pentium 4-M 1.8GHz processor,
> although I was listening to banging tunes and using the information
> superhighway at the same time. It was rendered with antialiasing settings:
> A0.3 and AM2. I hope it isn't too unbalanced, brightness-wise, as this
> laptop's screen is absolutely horrible.
> 
> This is quite a simple scene and the method can be expected to slow down
> considerably as scene complexity increases. Having said that, it's not as
> slow as I thought it might be despite the number of samples I'm using.
> After introducing the ability to change the size of the sampling
> hemisphere, which should allow me to reduce the number of samples used, I
> plan to think about the best way to integrate this into POV's materials
> system. At the moment it basically acts the same way as the finish term
> ambient does. Also, full occlusion is always black and zero occlusion is
> always white, whereas most apps allow the user to choose.
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
Do you realise that's what we call "radiosity" in POV-Ray? And that those so 
caled "ambient oclusion" are automaticaly generated using by that radiosity 
algorythm? It just need dome tweaking of the available parameters.

-- 
Alain
-------------------------------------------------
Never underestimate the power of stupid people in large groups.

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