Examining the demo code

Let's quickly explore the demo code. Do not worry about understanding everything just yet; we will cover each element in depth later. At this point, I am hoping you will acclimatize to the development environment and pick up a few things along the way. If you are stuck, keep going! Things will actually get simpler in the next chapter, once we clear away the SpriteKit demo and start on our own game.

Make sure you have GameScene.swift open in Xcode.

The demo GameScene class implements some functions you will use in your games. Let's examine these functions. Feel free to read the code inside each function, but I do not expect you to understand the specific code just yet:

• The game invokes the didMove function whenever it switches to the GameScene. You can think of it a bit like an initialize, or main, function for the scene. The SpriteKit demo uses it to draw the Hello, World text to the screen and set up the spinning square shape that shows up when we tap.
• There are seven functions involving touch, which handle the user's touch input to the iOS device screen. The SpriteKit demo uses these functions to spawn the spinning square wherever we touch the screen. Do not worry about understanding these functions at this time.
• The update function runs once for every frame drawn to the screen. The SpriteKit demo does not use this function, but we may have reason to implement it later.