Creating a 3-D game engine is not a trivial task as gamers often demand for high quality output with top notch performance in games. In this paper, we show you how various real-time rendering algorithms can be applied to implement a practical 3-D game engine. We explore the general architecture of a 3-D engine and discuss the role of a scene graph in a 3-D engine. We will look at scene graph from the software engineering perspective. In particular, we show you the way to design a scene graph that is object-oriented and portable across different rendering engine. Then, we explain the algorithms that we apply to speed up the performance of our 3-D engine. We optimize the 3-D engine on the scene graph and object geometry levels. The algorithms that we propose are expected to perform reasonably well for both static and dynamic scenes. Finally, we give you a brief preview on the possibility of parallel processing in scene graph to create a 3-D engine with multiprocessing capability.