Stencil jumping, the principle
Consider one element of a 2 dimensional mesh, for simplicity and consider a point O inside. The mesh element vertices are denoted by A,B,C and D and the vectors AB,BC,CD,DA,OA,OB,OC and OD are represented. The cross product of OA and AB will yield a vector perpendicular to the plane coming out of the monitor.We say that the cross product is postive.It will be observed that the cross products of OB and BC,OC and CD; and OD and DA are all positive.
This is not the case when the point is outside.
Here we see that, all the cross products are not positive.This is the major testing criterion in the alogrithm.