Facebook's Paper app is, in part, known for its slick animations, and now the company has taken the engine responsible for its smooth transitions open source for iOS. Pop, as the engine is known, uses dynamic animations to take the traditional animation framework Apple provides a step further, according to Facebook engineer and Push Pop Press co-founder Kimon Tsinteris.

Now available on GitHub, Pop makes use of the Apple provided Core Animation, of which Tsinteris feels is quite powerful and "simple to leverage" and takes it to the next level with a more natural gesture and velocity sensitivity. "With Pop, we are able to keep the familiar and powerful programming model of Core Animation while also capturing a gesture’s velocity and better reflecting user intent.”

In addition to the static animation types already available, Pop can offer developers 3 new animation types referred to as spring, decay, and custom. You can see the spring animation type in action with Paper's bouncing elements and decay, as you would imagine, allows for a smooth velocity sensitive stop in scroll motion, for example.

Pop also supports custom animation so developers can bring in their own code to make unique effects. "The API allows quick integration with existing Objective-C codebases and enables the animation of any property on any object," according to the Pop GitHub page. Anyone already comfortable with Core Animation will feel right at home with Pop, according to Facebook.