XVMUL3D returns one element of an input vector (x,y,z) multiplied by an input rotation matrix r(4,4).
value = XVMUL3D (n,x,y,z,v,r) n (I) : which coordinate value to return (1=x,2=y,3=z) x,y,z (R) : input x,y,z v (R) : working vector (4 elements) r (R) : rotation matrix (4,4) value (R) : desired element value (see n)