Import Geant4 10.4.0 source tree

source/analysis/g4tools/include/tools/lina/geom2

@@ -89,6 +89,43 @@ inline bool inside(const std::pair<T,T>& a_P,const std::vector< std::pair<T,T> >
   return ((wn!=0)?true:false);
 }
 
+template <class VEC2>
+inline bool intersect(const VEC2& P1,const VEC2& Q1,const VEC2& P2,const VEC2& Q2,VEC2& a_out) {
+  // (P1,Q1) first line, (P2,Q2) second line and a_out intersection.
+  // return false if no intersection. (For exa, parallel lines).
+
+  // P1+(Q1-P1)*r = P2+(Q2-P2)*s
+  // (Q1-P1)*r - (Q2-P2)*s = P2-P1
+  // r*(Q1-P1).v0 - s*(Q2-P2).v0 = (P2-P1).v0 //x
+  // r*(Q1-P1).v1 - s*(Q2-P2).v1 = (P2-P1).v1 //y
+  
+  // a*r + b*s = c
+  // d*r + e*s = f
+
+  // r = (c*e-f*b)/(a*e-d*b)
+  // s = (a*f-d*c)/(a*e-d*b)
+
+  typedef typename VEC2::elem_t T;
+  VEC2 A = Q1-P1;
+  VEC2 B = P2-Q2;
+  VEC2 C = P2-P1;
+
+  T a = A.v0();
+  T b = B.v0();
+  T c = C.v0();
+  T d = A.v1();
+  T e = B.v1();
+  T f = C.v1();
+
+  T det = a*e-d*b;
+  if(det==T()) return false;
+
+  T r = (c*e-f*b)/det;
+
+  a_out = P1+A*r;
+  return true;
+}
+
 }
 
 #endif