[FEAT] add tuple reflect

raytracing/src/tuple.cpp

@@ -331,6 +331,13 @@ Tuple Tuple::cross(const Tuple &a_tuple)
 
 /* ------------------------------------------------------------------------- */
 
+Tuple Tuple::reflect(const Tuple &a_normal)
+{
+    return *this - a_normal * 2 * dot(a_normal);
+}
+
+/* ------------------------------------------------------------------------- */
+
 void Tuple::set_at_index(uint8_t an_index, double a_value)
 {
     if (an_index == 0)

raytracing/src/tuple.h

@@ -87,6 +87,8 @@ namespace Raytracer
         double dot(const Tuple &a_tuple);
         Tuple cross(const Tuple &a_tuple);
 
+        Tuple reflect(const Tuple &a_normal);
+
     private:
         void set_at_index(uint8_t an_index, double a_value);
 

tests/06_light_shading.cpp

@@ -168,3 +168,47 @@ SCENARIO("Computing the normal on a transformed sphere", "[features/spheres.feat
         }
     }
 }
+
+/* ------------------------------------------------------------------------- */
+
+SCENARIO("Reflecting a vector approaching at 45°", "[features/tuples.feature]")
+{
+    GIVEN("v <-vector(1, -1, 0)")
+    {
+        Tuple v = Tuple::Vector(1, -1, 0);
+        AND_GIVEN("n <-vector(0, 1, 0)")
+        {
+            Tuple n = Tuple::Vector(0, 1, 0);
+            WHEN("r <- reflect(v,n)")
+            {
+                Tuple r = v.reflect(n);
+                THEN("r = vector(1,1,0)")
+                {
+                    REQUIRE(r == Tuple::Vector(1, 1, 0));
+                }
+            }
+        }
+    }
+}
+
+/* ------------------------------------------------------------------------- */
+
+SCENARIO("Reflecting a vector off a slanted surface", "[features/tuples.feature]")
+{
+    GIVEN("v <-vector(0, -1, 0)")
+    {
+        Tuple v = Tuple::Vector(0, -1, 0);
+        AND_GIVEN("n <-vector(sqrt(2)/2, sqrt(2)/2, 0)")
+        {
+            Tuple n = Tuple::Vector(sqrt(2) / 2, sqrt(2) / 2, 0);
+            WHEN("r <- reflect(v,n)")
+            {
+                Tuple r = v.reflect(n);
+                THEN("r = vector(1,0,0)")
+                {
+                    REQUIRE(r == Tuple::Vector(1, 0, 0));
+                }
+            }
+        }
+    }
+}