As I was developing the ABC of the Sea App, which is an interactive picture-book based on a proof-of-concept Tara (my wife) made many years ago and did not publish, one of the early and obvious items on the checklist of cool things it should do is have a nice page curl transition when moving between pages. Initially I expected this to be easy – Apples Apps do this, iBooks on the iPad especially, so it’s built in, right?
Wrong. Well, mostly wrong. I quickly discovered that the only documented curling transition for a UIView goes up/down, not left/right. It’s the one that Maps uses. Some Googling then revealed that an undocumented transition did perform left/right curling. However, being undocumented means it’s not viable for an App Store submission. It may later acquire an official constant and become kosher, but not yet.