OpenGL ES does not have a built in library for curve generation, and while the formulas for creating curves can be readily found there are so many different types and it is always nice to have everything done for you. Core Animation provides a few different types of curves, but there are many more. I found out about some great open source code that performs the necessary calculations for 22 different types of curves. In case you’re wondering why you might need this data — it is extremely useful for animation. Also, this is not only an OpenGL curve library, you can use the functions for different Core Animation curves also.
The library is from Jeff Lamarche, co-author of Beginning iPhone 3 Development and More iPhone 3 Development books you can find out more about the functions, and see some of the examples of the curves at:
More Animation Curves Than You Can Shake A Stick At
Further information on how to use the functions can be found at the above link.