I guess it is similar, but lighting dependent, you need a 2 pass render?.
How would you account for the initial deposition type e.g. fallout, using 
your methodology?

In another way it is different as it does not have a zmap bias to the 
effect as I have described it. Diffuse reflection is related yet again not 
exactly the same.

I don't think my idea can actually be done in POV yet, but perhaps the 
radiosity code is a starting point for the required functionality?

There a 4 parts,
the deposition value ( from the "dirt projectors" ),
the point's view,
and the weighting of the view values based on distance from the point.
There needs to be a directional bias value to simulate the direction of any 
"cleaning". This vector and it's calculation offers all sorts of new 
possibilities if it is not constant for the entire object.
i.e you could have dirt fall onto the object and then be rubbed of with a 
swirling like pattern or a back and forth motion.

This allows the calculation for the final grime mask,
dirt minus cleaning
With zbias being vital for filling small details on larger flat areas.
I guess all the calculations need to be post displacement etc. and should 
be compatible with a simple bump too.

This cleaning value could also be used separately to control such things as 
dent and scratch representations.

If implemented in an open enough form it could have many uses.

Kari Kivisalo wrote:

> Daniel Matthews wrote:
>>
>> i.e in a hollow where things collect you can see the rim edge, but on a
>> hill you can't, the deeper and more narrow you hollow the more of the sky
>> is obscured by the surrounding walls. So on a hill top all the grime is
>> removed as it has no shelter.
> 
> This is exactly what I did with the radiosity patina. When
> recursion_level 1 is used the illumination on the surface
> tells directly how much "outside" is visible from that point.
> 
> news://news.povray.org/3B8DD549.D0A9588E%40engineer.com
> news://news.povray.org/3B8E0F26.6DDC17B3%40engineer.com
> 
> 
> _____________
> Kari Kivisalo

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