Finally found the root of that off by one error. Changed up the readme.

include/util.hpp

@@ -13,15 +13,6 @@
 const double PI = 3.141592653589793238463;
 const float  PI_F = 3.14159265358979f;
 
-struct Light {
-	sf::Vector4f rgbi;
-
-	// I believe that Vector3's get padded to Vector4's. Give them a non-garbage value
-	sf::Vector3f position;
-
-	sf::Vector3f direction_cartesian;
-};
-
 struct fps_counter {
 public:
 	fps_counter(){
@@ -273,4 +264,27 @@ inline std::vector<float> sfml_get_float_input(sf::RenderWindow *window) {
 
 	return ret;
 
-}
+}
+
+struct Light {
+	sf::Vector4f rgbi;
+
+	// I believe that Vector3's get padded to Vector4's. Give them a non-garbage value
+	sf::Vector3f position;
+
+	sf::Vector3f direction_cartesian;
+
+	void look_at_center() {
+		direction_cartesian = SphereToCart(CartToNormalizedSphere(sf::Vector3f(256, 256, 256) - position));
+	};
+
+	void orbit_around_center(double time) {
+		position = sf::Vector3f(
+			position.x * cos(time/1000) - position.y * sin(time/1000),
+			position.x * sin(time/1000) + position.y * cos(time/1000),
+			position.z
+		);
+
+		look_at_center();
+	};
+};