#macro TestIsect(A, B, C, P, Q)
   #local AB = B - A;
   #local AC = C - A;
   #local N = vcross(AB, AC);

   #local PQ = Q - P;

   #local _t = vdot(N, A - P) / vdot(N, PQ);

   #local Isect = ((_t >= 0) & (_t <= 1));

   #if (Isect)
     #local I = P + PQ*_t;

     #local AI = I - A;
     #local J = vcross(N, AB);
     #local K = vcross(N, AC);
     #local _u = vdot(AI, K) / vdot(AB, K);
     #local _v = vdot(AI, J) / vdot(AC, J);

     #local Isect = ((_u >= 0) & (_v >= 0) & (_u + _v <= 1));
   #end

   Isect
#end

Andrew.

PS. Annoying that I have to put the underscores on those variable 
names... grrr!

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