There are three quick items to take care of before we start drawing. To begin the preparation, go through the following steps:

I will provide two checkpoints per chapter, each with a link to download the sample code at that point in time. I hope this will help you move forward if you are stuck or want to check your code against mine. If you want to download the sample project upto this point, you can do so from http://www.joyfulgames.io/chapter-2

It is time to write some game code-fantastic! Open your GameScene.swift file and find the didMove function. Recall that this function fires every time the game switches to the GameScene. We will use this function to get familiar with the SKSpriteNode class. You will use SKSpriteNode extensively in your game whenever you want to add a new 2D graphic entity.

Let's begin by drawing a blue square on the screen. The SKSpriteNode class can draw both texture graphics and solid blocks of color. It is often helpful to prototype your new game ideas with blocks of color before you spend time on artwork. To draw the blue square, add an instance of SKSpriteNode to the game:

override func didMove(to view: SKView) { 
    // Make the scene position from its lower left 
    // corner, regardless of any other settings: 
    self.anchorPoint = .zero 
 
    // Instantiate a constant, mySprite, instance of SKSpriteNode 
    // The SKSpriteNode constructor can set color and size 
    // Note: UIColor is a UIKit class with built-in color presets 
    // Note: CGSize is a type we use to set node sizes 
    let mySprite = SKSpriteNode(color: .blue, size: 
    CGSize(width: 50, height: 50)) 
 
    // Assign our sprite a position in points, relative to its 
    // parent node...

Before we dive back in to sprite theory, we should have some fun with our blue square. SpriteKit uses action objects to move sprites around the screen. Consider this example: if our goal is to move the square across the screen, we must first create a new action object to describe the animation. Then, we instruct our sprite node to execute the action. I will illustrate this concept with many examples in the chapter. For now, add this code in the didMove function, below the self.addChild(mySprite) line:

// Create a new constant for our action instance 
// Use the move action to provide a goal position for a node 
// SpriteKit will tween to the new position over the course of the 
// duration, in this case 5 seconds 
let demoAction = SKAction.move(to: CGPoint(x: 300, y: 150), 
duration: 3) 
// Tell our square node to execute the action! 
mySprite.run(demoAction) 

Run the project. You will see our blue square slide across...

SpriteKit uses a grid of points to position nodes. In this grid, the bottom left corner of the scene is (0,0), with a positive x-axis to the right and a positive y-axis to the top.

Similarly, on the individual sprite level, (0,0) refers to the bottom left corner of the sprite, while (1,1) refers to the top right corner.

You may want to take a screenshot of your blue box for your own enjoyment later. I absolutely love reminiscing over old screenshots of my finished games when they were nothing more than simple colored blocks sliding around the screen. Now it is time to move past that stage and attach some fun artwork to our sprite.

You may notice that our bee image is quite blurry. To take advantage of retina screens, assets need to be twice the pixel dimensions of their node's size property (for most retina screens), or three times the node size for the Plus versions of the iPhone. Ignore the height for a moment; our bee node is 100 points wide, but the PNG file is only 84 pixels wide. The PNG file needs to be 300 pixels wide to look sharp on the Plus-sized iPhones, or 200 pixels wide to look sharp on 2X retina devices.

SpriteKit will automatically resize textures to fit their nodes, so one approach is to create a giant texture at the highest retina resolution (three times the node size) and let SpriteKit resize the texture down for lower density screens. However, there is a considerable performance penalty, and older devices can even run out of memory and crash from the huge textures.