CORRECTION: "is INVERSELY proportional to the amount of the same object 
that is visible" 

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.

Daniel Matthews wrote:

> I was thinking about grime etc. and I had the following idea.
> 
> For any given spot on an object,
> the amount of deposited grime that can be rubbed off,
> is proportional to the amount of the same object that is visible,
> from that point with a 180 degree FOV looking along the current normal,
> with a bias controlled by the zmap of that view.
> 
> I guess the "dirt camera" resolution is equivalent to "number of samples",
> so you can speed up the calculations by lowering the accuracy.
> 
> For the ultimate grime you would not just test for "self" but for all
> objects within a given distance, that could influence the deposit, but
> this would be slower again.
> 
> Initial dirt deposits could be controlled with a dirt source that would
> work very much like a light source that is more or less diffuse. This
> would allow for everything from a wet spray look to a soft dust effect.
> Obviously the concept of "up" would need to be factored in too.
> 
> I can see this in my head, clearly, I hope my words make as much sense to
> you.
> 
> :o)
> 
> Can anyone else see what I mean?

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