Group should work now.

source/include/shape.h

@@ -58,7 +58,7 @@ public:
 
     void updateTransform();
     Tuple worldToObject(Tuple point) { return this->inverseTransform * point; };
-    Tuple normalToWorld(Tuple normalVector) { return (this->transposedInverseTransform * normalVector).normalise(); };
+    Tuple normalToWorld(Tuple normalVector);
 
     void setTransform(Matrix transform);
     void setMaterial(Material material) { this->material = material; };

source/intersect.cpp

@@ -24,6 +24,7 @@ Intersect::Intersect()
 Intersect::~Intersect()
 {
     /* Free stuff */
+    free(this->list);
 }
 
 void Intersect::add(Intersection i)

source/pattern.cpp

@@ -18,7 +18,7 @@ Pattern::Pattern(Colour a, Colour b): a(a), b(b)
 
 Colour Pattern::patternAtObject(Shape *object, Tuple worldPoint)
 {
-    Tuple objectPoint = object->inverseTransform * worldPoint;
+    Tuple objectPoint = object->worldToObject(worldPoint);
     Tuple patternPoint = this->inverseTransform * objectPoint;
 
     return this->patternAt(patternPoint);

source/shapes/shape.cpp

@@ -27,18 +27,25 @@ Intersect Shape::intersect(Ray r)
     return this->localIntersect(this->invTransform(r));
 };
 
-Tuple Shape::normalAt(Tuple point)
+Tuple Shape::normalToWorld(Tuple normalVector)
 {
-    Tuple local_point = this->inverseTransform * point;
+    Tuple world_normal = this->transposedInverseTransform * normalVector;
-
-    Tuple local_normal = this->localNormalAt(local_point);
-
-     Tuple world_normal = this->transposedInverseTransform * local_normal;
 
     /* W may get wrong, so hack it. This is perfectly normal as we are using a 4x4 matrix instead of a 3x3 */
     world_normal.w = 0;
 
     return world_normal.normalise();
+};
+
+Tuple Shape::normalAt(Tuple point)
+{
+    Tuple local_point = this->worldToObject(point);
+
+    Tuple local_normal = this->localNormalAt(local_point);
+
+    Tuple world_normal = this->normalToWorld(local_normal);
+
+    return world_normal;
 }
 
 void Shape::updateTransform()

tests/shape_test.cpp

@@ -133,12 +133,34 @@ TEST(TestShape, Converting_a_normal_form_object_to_world_space)
     s.setTransform(translation(5, 0, 0));
     g2.addObject(&s);
 
-    Tuple p = s.normalToWorld(Point(sqrt(3)/3, sqrt(3)/3, sqrt(3)/3));
+    Tuple p = s.normalToWorld(Vector(sqrt(3)/3, sqrt(3)/3, sqrt(3)/3));
 
     /* Temporary lower the precision */
     set_equal_precision(0.0001);
 
-    ASSERT_EQ(p, Point(0.2857, 0.4286, -0.8571));
+    ASSERT_EQ(p, Vector(0.2857, 0.4286, -0.8571));
+
+    set_equal_precision(FLT_EPSILON);
+}
+
+
+TEST(TestShape, Finding_the_normal_on_a_child_object)
+{
+    Group g1 = Group();
+    g1.setTransform(rotationY(M_PI / 2));
+    Group g2 = Group();
+    g2.setTransform(scaling(1, 2, 3));
+    g1.addObject(&g2);
+    Sphere s = Sphere();
+    s.setTransform(translation(5, 0, 0));
+    g2.addObject(&s);
+
+    Tuple p = s.normalAt(Point(1.7321, 1.1547, -5.5774));
+
+    /* Temporary lower the precision */
+    set_equal_precision(0.0001);
+
+    ASSERT_EQ(p, Vector(0.2857, 0.4286, -0.8571));
 
     set_equal_precision(FLT_EPSILON);
 }