This week, Facebook will host its first developer-oriented conference since its IPO, and the days leading up to it will surely see a bunch of announcements.

Up first: The social network is now open-sourcing Pop, the animation engine behind its Paper app.

Facebook launched Paper about three months ago as a new way for people to read and enjoy their News Feed content in an image-rich, magazine-like interface. The app also has smooth transitions and animations, derived from mobile app-maker Push Pop Press‘s technology.

Pop uses dynamic instead of traditional animations to create the various interactions found in Paper, which iOS has supported very well since its beginnings. Apple’s Core Animation framework “makes linear, ease-in, ease-out, and ease-in-ease-out animations simple to leverage,” Push Pop Press cofounder Kimon Tsinteris said in a blog post.

“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,” writes Tsinteris.

Facebook Pop animations

The Pop engine aims to offer three advantages to developers. First, it aims to make animations “extremely convenient,” adding the “Spring,” “Decay,” and “Custom” animations to the four traditional static ones.

“Spring” yields the bouncy animation found in Paper, and “Decay” brings the movement to a “slow halt.”

Facebook Pop animations 2

Second, Facebook designed Pop to be an extensible framework. Developers can plug in their own code into Pop to create custom and unique animations and effects. “Pop can animate any property of any Objective-C object,” offering huge flexibility and scope to the framework.

And lastly, Facebook wanted Pop to be as developer-friendly and quick to dive into as possible. Its API is very similar to Core Animation’s, making it easy for developers to easily start using the engine in their work. The official blog post offers more details about this.

Facebook acquired Push Pop Press in 2011, tiny outfit cofounded by former Apple employees Mike Matas and Kimon Tsinteris. Push Pop Press created a popular iPad app called Our Choice, and Facebook scooped up the company to weave in its technology into the social network itself.

The acquisition was about “giving people even richer ways to share their stories,” as Facebook said at the time. Today, this will no longer be limited to Facebook content.

Facebook has previously also open-sourced KVOController, Shimmer, and Tweaks for iOS, among many other innovative pieces of software.

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