We plan to add this in the future. But it’s not as straightforward as it might sound.
Apple only provides one API to add this kind of transition, and it’s super outdated. It’s been around since iOS 5.
We use a completely different approach to implement the readers. This means that, if we want to add this transition, we have to create an entirely new reader using UIPageViewController.
We have always been reluctant to add it because of a few reasons:
The UIPageViewController is very old, and Apple hasn’t updated it in many years. I wouldn’t be surprised if that API gets deprecated in the future. Building on top of it is high risk. If Apple deprecates it, it would throw away many hours of work.
Apple hasn’t implemented the curl transition in any modern APIs. Actually, there isn’t any curl animation in SwiftUI APIs, which is a clear sign of where we are going.
The age of skeuomorphism ended long ago and feels out of place in modern design. Apple has been pushing for removing skeuomorphic elements from UIKit for years.
That said, we know some of you are quite passionate about it. And given that it requires a separate implementation and won’t affect the rest of the reading modes, we will add it as soon as we have time.
But keep in mind that we are dealing with 12 years old APIs. Ideally, Apple’s step back with the Books app means they have re-thought the whole thing and plan to keep its official support. But IMHO, the step back is just a Marketing/PR move to reduce the backlash they got from the recent releases, not a strategic decision of the Design Team. I’m sure they are still planning to remove it at some point.
Don’t get me wrong; I have nothing against that animation. I’m happy to have it in Panels if Apple provides a way and it’s easy to coexist with the rest of the app parts. But I’m quite pessimistic about it. Unless something changes at Apple, the future doesn’t look good for the curl animation fans.