I'm trying to implement some of the techniques described in this article for culling objects during shadow map generation. In particular I'm trying to get working the method of computing the projected shadow caster bounding volumes to cull objects that may be visible to a light frustum but don't actually cast a shadow into the camera view frustum. The author describes this as follows:
Therefore, if shadow casting objects are represented as bounding boxes, a frustum can be used to represent the projected shadows, and we can reuse the frustum-frustum culling test developed above.
To build this frustum, the demo computers a tight bounding cone surrounding the light position and each shadow caster's world-space bounding box. This cone is trivially converted into a centered frustum.
It sounds like he's describing a cone with vertex at the light position that extends towards the object and encloses its bounding box. However this volume definitely will not contain the shadow projected by the object (since the shadow will going to extend beyond the object in the direction of the light).
The attached figure is in the chapter, showing the case that this technique is meant to allow us to cull, complete with a picture of a frustum that looks like the one described which doesn't look very helpful for deciding to cull that object.
I don't have the source code to the demo so I can't be sure what his exact implementation looks like. Does anyone else have another interpretation of this that makes more sense?