Angus Dorbie (dorbie++at++multipass)
Mon, 29 Dec 1997 09:33:21 -0800
For the lighting term you rely on the accurate placement of light
sources, however lighting is a per vertex calculation.
You could consider a scheme where a 3 dimensional texture was
used for range attenuation where the third texture axis modulated
from white to black. The idea here is to ensure that the total
energy is constant over the area of the light lobe at any
orthogonal cross section (or less with atmospheric effects).
The exact distribution of r with depth would depend on the field
of view and the information in the 3D texture, there's more than
enough flexibility to apply what you need although you may have
to scale everything since currently s & t are divided by r for
the projective effect so a normalized projective texture would
be required and you may need several slices in the 3D texture
to get the dropoff right although you may want to have several
slices in the 3D texture.
The L.N illumination term would be produced by a distant light
source along the lobe vector and you wouldn't need per pixel
illumination. The combination of this and the range + lobe
attenuation is a good approximation of per pixel lighting for
almost all circumstances, at least for the diffuse case. The
biggest errors would be in the specular term.
Cheers,Angus.
On Dec 29, 4:56pm, flysiml++at++public.bta.net.cn wrote:
> Subject: spotlight lobe......how to make it fade out by the range
> Thank Angus for reply on my last problem. And here is another
> one about spotlight:
>
> in Performer 2.2 I use pfLightAtten() and pfSpotLightCone() to
> try to make the spotlight lobe dark out when the distance is
> more than 100m from the source. But nothing happend. The spotlight
> can lit the object as far as the clouds on the sky.
>
> Please help.
>
> Thanks
>
> Cao Zhigang
>
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