Comment by kridsdale3

I suspect the specific versions you call out were in that time period for a reason.

Snow Leopard was the first to integrate iOS's CoreAnimation framework. Nearly all animations now are based on that. Before, the CPU manually updated the sizes and positions of things, frame by frame, in a loop. This is how you'd program a Game Engine.

After, with CA, state-change property models are sent to a different process entirely which does its own interpolation to animate the UI at a higher thread-priority than any other process in the operating system. This is fantastic if maintaining 60+ FPS at all times, even on an iPhone 1 or 3G with less power than you'd have in today's AirPod chips, was a central requirement. (And it was, the first iPhones dominated their competitors in terms of input latency and framerate)

But programming CoreAnimation is much more complicated and easy to make mistakes in if you want "every frame perfect". Trust me, I made a lot of the animations that shipped in iOS 7 (the Calendar app is full of them, OS level transitions for the core chome elements of iOS). It took nearly a year of meticulousness to get things looking ok. In the years since I left the company, I've noticed these transitions get more and more janky and buggy and full of artifacts. Clearly, whoever replaced me doesn't have the same eye and sense of craft. Oh well.