I'm teaching myself Mac OS X programming, and have decided to write all new Mac code in Objective-C using Cocoa. However, I have a very large library of C++ classes that I do not want to port to ...

Using a single C++ codebase you can deploy games to just about any mobile platform and since Cocos2d-x is open-source, you can tweak the game engine if needed.The Cocos2d API is simple and powerful.