Pop brought dynamic animations to the iPhone and enabled Facebook to bring a UIScrollView experience to Paper.
Since the original iPhone, iOS has excelled at supporting static animations. The Apple-provided Core Animation framework makes linear, ease-in, ease-out, and ease-in-ease-out animations simple to leverage.
The innovation of touch interfaces has ushered in a new wave of software design. Direct manipulation of on-screen elements has removed one level of indirection, which in turn has raised our expectations for the screen as a medium. If objects respond to our touches, they should also respond to the velocity of our flick.
When I co-founded Push Pop Press in 2010, our goal was to create a realistic, physics-everywhere experience. We wanted a solution that would allow us to evoke the same delightful experience of UIScrollView throughout the whole application. Pop is the latest manifestation of that vision, allowing us to keep the familiar and powerful programming model of Core Animation, while also capturing a gesture’s velocity and better reflecting user intent. Paper has given us the opportunity to further refine both the vision and the animation engine behind it.
We wanted to make commonly needed animations extremely convenient. In addition to the four established static animations, Pop introduces three new primitive animation types: spring, decay, and custom.