William F Pokorny <ano### [at] anonymousorg> wrote:

> By using a positive light and a negative light at the same position
> where the fade distance of the negative light is slightly inside the
> positive one, and where both have very high fade powers, we can 'see'
> what non-shadowed surfaces are at a certain distance from the light
> source position.

Hi Bill,
That's a very cool idea!  :)
Just to raise the bar a bit - is there any way that you can think of to simulate
an interference pattern?  Is there a way to [de facto] define a pattern for the
light_source such that one can [faux]cancel the other?
Off the top of my head, I'd say that it would have to be standard light source,
and a distance function-based pigment like Christoph suggested coupled with a
sin function...

But:  Couldn't you just enclose the entire scene into a union, and use an onion
pattern?

Define a color map with a narrow band of white, and the rest is rgbt 1, and then
scale it to highlight the desired distance.

I suppose you could also define a color map for the onion pattern going from 0
to 1, and then scaling it to the maximum desired radius.  The color value at any
point would then be the distance from wherever you translated the center of the
onion pattern to.

At the moment, I think the only way to indirectly find the total ray path length
is the formula method suggested by Christoph, but that's only for direct
lighting.  The ray path length for a light reflected from a mirror that hits an
object and then travels to the camera (ok, it's the reverse of that for
raytracing...) I think might presently be a challenging task.

Let me know if any of this has merit, or I'm in error.

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