Re: [Algorithms] Silhouette determination for the world's shadow volume

[Jeff R. <je...@8m...>]

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 <
Dam...@m8...> 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