Ben Birdsey <cla### [at] netscapenet> wrote:
: 	Right now, radiosity is just a way of calculating the AMBIENT light at
: different points.  This is the same reason the slope mapped texture
: doesn't show with ambient light either.  ( turn the radiosity off and
: crank up the "ambient_light" in "global_settings" and check it out).

  I think that you are a bit wrong here.

  You are right when saying that radiosity (or whatever it should be called)
is used for calculating ambient light. But that's more than just calculating
the brightness of the scene in a certain point. It actually calculates how
light bounces from surfaces and how does it illuminate the current point.
This means that the color and the angle of incidence of the surfaces affect
the color and the brightness of the reflected light.
  If we have a sphere in the shadows, the part of the sphere which is facing
the bright white wall will be more illuminated that the part of the sphere
which is perpendicular to the wall.
  Plain ambient light would just apply a constant brightness to the whole
sphere.

  In the example scene I posted there are two gaps in the wall. None of them
is visible in the shadowed part without radiosity, regardless of how high
we set the ambient_light.
  With radiosity the left gap becomes visible because its surface normals
are different from the wall. The surface of the gap that is facing the red
wall will be slightly tinted red while the other surface will be slightly
tinted blue. The gap will also be a little bit darker than the wall because
it receives less light.
  Now, the other gap is almost exactly identical to the first one. The only
difference is that the normals of the gap are created in a different way.
Instead of being surface normals they are patterned normals. Povray treats
both gaps almost identically when calculating regular lighting. I don't
understand why should it treat them differently when calculating radiosity.

: 	2) Talk to Nathan really nicely and see if he would
: 	   rewrite the radiosity code to use a kD tree and
: 	   photon map.  Now that would be cool!

  I think that Nathan has already tried using photon mapping for radiosity.
AFAIK it's a pretty inefficient way of doing it (most photons will be shot
and stored although their contribution to the lighting is almost none).
The stochastic method is much more efficient (at least in the way Nathan
has made it).

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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