Add vector reflection via a normal vector.

source/include/tuple.h

@@ -41,8 +41,8 @@ public:
     double magnitude();
     Tuple normalise();
     double dot(const Tuple &b);
-
     Tuple cross(const Tuple &b) const;
+    Tuple reflect(const Tuple &normal);
 };
 
 class Point: public Tuple

source/tuple.cpp

@@ -33,4 +33,9 @@ Tuple Tuple::cross(const Tuple &b) const
                  this->z * b.x - this->x * b.z,
                  this->x * b.y - this->y * b.x,
                  0);
+}
+
+Tuple Tuple::reflect(const Tuple &normal)
+{
+    return *this - normal * 2 * this->dot(normal);
 }