iOS Core Animation: Advanced Techniques

1. The Layer Tree

Ogres have layers. Onions have layers. You get it? We both have layers.

Shrek

Core Animation is misleadingly named. You might assume that its primary purpose is animation, but actually animation is only one facet of the framework, which originally bore the less animation-centric name of Layer Kit.

Core Animation is a compositing engine; its job is to compose different pieces of visual content on the screen, and to do so as fast as possible. The content in question is divided into individual layers stored in a hierarchy known as the layer tree. This tree forms the underpinning for all of UIKit, and for everything that you see on the screen in an iOS application.

Before we discuss animation at all, we’re going to cover Core Animation’s ...