Re: Silhouette determination for the world's shadow volume

Remember also that the shadow volumes for static world geometry vs
fixed-position lights are also static and can be created off-line. The
static volumes need to be extruded a distance based on the maximum
run-time intensity of the fixed position light sources.

If fill rate proves to be a bottleneck then the CC shadow volumes paper
(http://gamma.cs.unc.edu/CCSV/) would be worth a look. I've never tried to
implement the algorithm but it promises impressive reductions in fill
rate.

Cheers
Derek


> Well, the shadow volume mesh topology rules really aren't any different
> for
> light sources inside a mesh vs outside - as long as your geometry faces
> inwards (and it will), the idea is the same (find and extrude edges that
> border lit & unlit faces). Sometimes world geometry is stored in funny
> ways
> depending on your game/engine (BSP trees or what have you), that might
> make
> finding edges trickier, but the algorithm is the same.
>
> A good optimization for fill rate if you are using local light sources is
> to
> make sure and only extrude shadow volumes for the areas of the world that
> intersect the light's attenuation radius.
>
> Jeff
>
> On Sun, Apr 18, 2010 at 3:12 PM, Damian Coventry <
> [email protected]> wrote:
>
>> Morning,
>>
>> WRT shadow volumes, what's a common approach for determining the
>> silhouette for the world mesh?  Let's say it's an indoor only game. In
>> this case the camera and lights are both "inside" the world mesh, and
>> the world mesh is concave.
>>
>> For the other meshes that move around inside the world, silhouette
>> determination is well documented - "The set of all edges that connect a
>> toward-face to an away-face form the silhouette with respect to the
>> light source. The edges forming the silhouette are extruded away from
>> the light to construct the faces of the shadow volume".
>>
>> What about the world mesh though? My initial thoughts are to use all
>> world mesh polygons that don't face the light source, and create
>> individual shadow volumes for each polygon.  This would get costly if
>> the world mesh had many back facing polygons at any given time.  How
>> else is it done?
>>
>>
>> ~Damian();
>>
>>
>>
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>
>
>
> --
> Jeff Russell
> Engineer, 8monkey Labs
> www.8monkeylabs.com
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