This is something that is actually pretty tricky. The GPUs on many devices don't allow multiple OpenGL contexts to be created. So in the case of Android, the

This is something that is actually pretty tricky. The GPUs on many devices don't allow multiple OpenGL contexts to be created. So in the case of Android, the animations are done in software and the currently running application can create an OpenGL context. This generally makes for slow animations (and unfortunately worse battery life). What can be done is that the system can create an OpenGL context, and then proxy all other calls (from other apps) through that context with a minor performance hit. This is something that the original iPhone had actually done. However, I think this might be somewhat challenging when working with different mobile GPUs and their quirks. So while on the surface it's a very simple problem, in practice it can be very hard.