Brad Larson notes that Core Animation – Apple’s framework for hardware-accelerated animation – is built on top of OpenGL. Core Animation is typically used for 2D animations and effects, but Brad noted that:
[..] I realized that this layering meant that some of Core Animation’s functions could be used for more than just 2-D view animations. This started with a little proof-of-principle application I did where I translated the 3-D rotation mechanic in Molecules to Core Animation [..]
In “Improving OpenGL ES performance using CATransform3D” Brad explains how he used this realization and some smart coding to get a 14-25% increase in performance (in number of triangles per second that the iPhone’s GPU could render) using CATransform3D.