filtershadow VEX function
Sends a ray from the position P along direction D.
Contexts: displace, fog, light, shadow, surface

vector filtershadow(vector P, vector D, float bias)
Sends a ray from the position P along direction D. The length of the D vector represents the farthest distance considered when check for occlusion.
Each occluding surface will be evaluated and its opacity will be added to the total occlusion. The return code of this function is the total occlusion of shaded surfaces between the point P and the point specified by P + D.
See optional parameters .