Is there any API to test the Windows application?

I'm doing manual testing on Windows Application(Desktop) written in c++ in 2000. This application uses OpenGL to draw Image(UI). The application is very old and I was thinking to do automation that would perform the mouse click, keyboard, position identification of content and then test it using a mouse. AutoIT does not work because the Window varies over execution and functionalities. Please tell me if there is any API, written especially c++, c# or any other language which can do unit testing on Windows Application. I use the windows 7 to perform the testing.