clip VEX function
clip the line segment between p0 and p1.
Contexts: image3d, chop, cop, pop, sop, surface, displace, fog, light, shadow, photon, cvex

void clip(int result&, vector p0&, vector p1&, vector4 plane)
clip the line segment against an arbitrary 3D plane specified by the plane equation (plane.x*x + plane.y*y + plane.z*z + plane.w).

void clip(int result&, vector p0&, vector p1&, vector min, vector max)
clip the line segment to the bounding box specified by the min and max corner points.
clip the line segment between p0 and p1.
If the line is entirely clipped out of the result will be set to 0. otherwise, the values p0 and p1 will be clipped to the constraints specified and the result will be 1.