Add max_depth parameter

src/scene.cc

@@ -16,6 +16,7 @@
 
 Scene::Scene()
     : width(640), height(480),
+      max_depth(5),
       pixels(NULL)
 { }
 

src/scene.h

@@ -42,10 +42,17 @@ public:
 private:
     Color trace_ray(const Ray &ray, const int depth);
 
+    // Pixel dimensions of the image.
     int width, height;
+
+    // Ray tracing parameters.
+    int max_depth;
+
+    // Scene objects.
     std::list<Shape *> shapes;
     std::list<Light *> lights;
 
+    // Rendering output.
     bool _is_rendered;
     Color *pixels;
 };