OpenGL is very good API to draw graphics. It provide lots of covered functions to make the programmer easy to draw graphics, for example, if you want to draw a box, you can just call the funtion box(10,10,10), then the app will draw a box with 10 centimeter high, 10 centimeter wide and 10 centimeter long for you, that is very convenient! For different OS, there also are their own graphic API, this kind of API always very efficient, but it is always very diffcult to understand! in a word, I like OpenGL very much. you can draw everything what you want by this API! forthmore, it can support any platform, so openGl will be developed quiukly in future and will be used as wide as possible!