"" <nomail@nomail> wrote:
> I'd like to show the intensity of light in free space for a physical
> simulation. I've thought to use a sort of "magic" plane that in the first
> stage of classical ray-tracing or radiosity calculation should be
> transparent to light and that in a second stage it should be used to
> evaluate the intensity of light.

Well, I think you're talking about applying a spherical texture to the
plane. What you need to do is make a texture with the "spherical" pattern.
Apply a colour map with a colour, like rgbt <1,1,0>*Intensity, to a band,
say, where density is in the range [0, 0.05]. Then just put a "scale
Radius" keyword into your plane texture declaration. Note that Radius and
Intensity are two variables which you declare earlier.

Hope I was clear enough on that point... Just make sure that if the source
of light from which you want to spread the pulse light sphere is not at
<0,0,0> that you scale the texture first, then translate. It doesn't work
the other way around (your sphere's center will move away from the origin
as you scale). Oh, and of course, when building your colour_map, make sure
you put transmissive colour in all other parts of the density map:

colour_map {
  [0.0 color rgb <1,1,0>*Intensity transmit 1-Intensity]
  [0.05 color rgb <1,1,0>*Intensity transmit 1-Intensity]
  [0.051 color rgb <1,1,0>*Intensity transmit 1]
  [1.0 color rgb <1,1,0>*Intensity transmit 1]
}

Can't make a whole scene example, but you get the picture.

The other way would be to make a difference of two spheres and applying a
translucent texture to them, then cutting half the sphere away. Even
thirdly, intersect the two spheres with a thin box.

Lots of different options, try one and you'll see what works best for you.

  -Klemen

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