A second distance d1 is computed between a second point of intersection p02 on triangle T0 and a first point
of intersection p12 on triangle T1. This distance d1 is relatively small in comparison to dmax, and consequently the
shadow cast on triangle T1 will be sharp and dark. To compute the second distance d1, the distance from the light
source to the intersection point p12 is held in the secondary depth buffer, and the distance from the light source to the intersection point p02 is held in the primary depth buffer.