Unlike UIKit, which is based on events and waits for user input before performing any drawing or interactions, Sprite Kit evaluates all nodes, their interactions, and physics as fast as it can (capped at 60 times per second) and produces results on screen. In the following figure, you can see the way a game loop operates:
First, the scene calls the
update:(CFTimeInterval)currentTime method and sends it the time at which this method was invoked. The usual practice is to save the time of the last update and calculate the time that it took from the last update (delta) to the current update to move sprites by a given number of ...