Make parallel lines

And make TODO for P2P

GCS/GCS.h

@@ -250,6 +250,9 @@ public:
     void clearByTag(int tagId, bool is_fixed_point = false);
     int addConstraint(Constraint* constr);
     void removeConstraint(Constraint* constr);
+    Constraint* get_last_constraint() {
+        return clist[clist.size() - 1];
+    }
 
     // basic constraints
     int addConstraintFixed(Point& p, int tagId = 0, bool driving = true);