The complete tutorial on how to render Buttons using OpenGL can be found here:
http://www.haroldserrano.com/blog/how-to-add-multi-image-button-in-a-game-using-opengl-es
Rendering Buttons using OpenG ES in iOS
Objective-C++MIT
The complete tutorial on how to render Buttons using OpenGL can be found here:
http://www.haroldserrano.com/blog/how-to-add-multi-image-button-in-a-game-using-opengl-es