Even if your game is 2d, the math behind this kind of lighting is 3d. I would recommend the book real-time rendering for all the basic stuff, it is really good and will explain all you need to know about normal mapping.

Even if your game is 2d, the math behind this kind of lighting is 3d. I would recommend the book real-time rendering for all the basic stuff, it is really good and will explain all you need to do normal mapping.