Re: volumetric spotlight

I don't have references but here are a few techniques in increasing complexity:

For viewers at a distance it is hard to beat the simplicity of 
billboard sprites. Just lock a billboard to the spotlight cone axis 
and use alpha blending to make the texture glow. Fade it out when the 
viewer gets close enough to make the effect cheesy.

Create an umbra mesh, a skirt that resembles the spot cone and fix it 
to the spotlight in space. Simple vertex coloring to fade the skirt 
at the far end can be very effective. Again render using alpha 
blending. Some simple pixel shader work using normal averaging and 
dot product can help to hide the edges of the mesh. If you have 
access to the depth buffer values, you can also fade out pixels that 
approach the near plane so they don't clip noticeably as the viewer 
passes through the cone.

The most complex approach is to write a ray-casting shader that 
integrates over distance travelled by each eye ray through the umbra 
volume. It is hard to get the results to overlap and intersect 
correctly with the rest of the scene unless you have some sort of 
unified rendering architecture built around ray-casting. Very pretty 
if you get it working, but very difficult to deploy without 
limitations coming back to get you later.


Cheers,
Darren




At 09:24 AM 3/24/2010, Jeff Russell wrote:
>Hey, anybody have any cool reference for how to render a volumetric 
>spotlight effect? I realize that full correct shadowing with 
>volumetric lighting might be kind of heavy duty, so I'm willing to 
>try something a little dirtier or with no shadows.
>
>Regards,
>
>Jeff
>
>
>--
>Jeff Russell
>Engineer, 8monkey Labs
><http://www.8monkeylabs.com>www.8monkeylabs.com
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