Index: lib/geo/ccw.cpp
==================================================================
--- lib/geo/ccw.cpp
+++ lib/geo/ccw.cpp
@@ -20,5 +20,20 @@
 
 // intersection of two line segments.
 bool cross(CMP p1, CMP p2, CMP P1, CMP P2) {
 	return ccw(p1,p2,P1)*ccw(p1,p2,P2)<=0 && ccw(P1,P2,p1)*ccw(P1,P2,p2)<=0;
 }
+
+
+// Intersection of two line segments, by p1+(*pos)(p2-p1) where 0<=*pos<=1.
+// only tested by local simple unittest. be careful.
+template<typename T>
+bool cross(const std::complex<T>& p1, const std::complex<T>& p2,
+           const std::complex<T>& P1, const std::complex<T>& P2, T* pos) {
+	if( ccw(p1,p2,P1)*ccw(p1,p2,P2)<=0 && ccw(P1,P2,p1)*ccw(P1,P2,p2)<=0 ) {
+		if(outer_prod(p2-p1, P2-P1) == 0)
+			return false; // parallel
+		*pos = outer_prod(P1-p1, P2-P1) / outer_prod(p2-p1, P2-P1);
+		return true;
+	}
+	return false;
+}