Thanks! About OpenGL I don't know if I'm a good example to follow, in my case I mostly needed to understand how to setup, send vertices to OpenGL, set colors, activate blending, once I figured that out I abstracted that stuff away in a Processing-like API (setColor, drawRect, translate...) so I could forget about all that stuff. I figured things out mostly by skimming through this book [1], looking at the Processing code base, OpenGL tutorials, Stack Overflow... For the odd texture I still use the Texture2D class from Apple's examples. Note that at the time there were not many good OpenGL libraries for iOS, now things are different, OpenFrameworks works on iOS, there's Cinder, etc. Had I started a year later I probably could have skipped all that stuff instead of building my own library.

[1] http://www.amazon.com/Mobile-3D-Graphics-Kaufmann-Computer/d... [2] http://processing.org/