Chapter 6. Generating a Never-Ending World

The unique challenge of an endless flyer-style game is in procedurally generating a rich, entertaining game world that extends as far as your player can fly. We will first explore level design concepts and tooling in Xcode; Apple added a built-in level designer to Xcode 6, allowing developers to arrange nodes visually within a scene. Once we become familiar with the SpriteKit level design methodology, we will create a custom solution to generate our world. In this chapter, you will build an entertaining world for our penguin game and learn how to design and implement levels in SpriteKit for any genre of game.

The topics in this chapter include the following:

• Designing levels with the SpriteKit scene editor

• Building encounters for Pierre Penguin

• Integrating scenes into the game

• Looping encounters for a never-ending world

• Adding the Power-up Star at random places

• Turning bronze coins into gold coins

Designing levels with the SpriteKit scene editor

The Scene editor is a valuable addition to SpriteKit. Previously, developers would be forced to hard-code positional values or rely on third-party tools or custom solutions for level design. Now, we can lay out our levels directly within Xcode by dragging and dropping sprites. We can create nodes, attach physics bodies and constraints, create physics fields, and edit properties directly from the interface.

Here is a simple example scene you might build by simply clicking and dragging:

In this example, I simply dragged and positioned sprites in the scene. If you are making an unsophisticated game, you can start in the scene editor rather than creating custom classes. By editing physics bodies in the editor, you can even create entire physics-based games in the editor, adding only a few lines of code for the controls.

Complex games require custom logic and texture animation for every object, so we will implement a system in our penguin game that...

Building encounters for Pierre Penguin

Endless flyer games continue until the player loses. They do not feature distinct levels; instead, we will design encounters (my own term) for our protagonist penguin to explore. We can create an endless world by stringing together encounters one after the other and randomly recycling from the beginning when we need more content.

The following diagram illustrates this basic concept:

A finished game might include twenty or more encounters to feel varied and random. We will create three encounters in this chapter in order to populate the encounter recycling system.

We will build each encounter in its own scene file, in the same way we would approach a separate level in a standard platformer or physics game.

Creating our first encounter

First, create an encounter folder group to keep our project organized. Right-click your project in the project navigator and create a new group named Encounters. Then, right-click on Encounters and add a new SpriteKitScene file...

Looping encounters for a never-ending world

We need at least three encounters to endlessly cycle and create a never-ending world; two can be on the screen at any one time, with a third positioned ahead of the player. We can track Pierre's progress and reposition the encounter nodes ahead of him.

Building more encounters

We need to build at least two more encounters before we can implement the repositioning system. You can create more if you like; the system will support any number of encounters. For now, add two more SpriteKit scene files to your game: EncounterB.sks and EncounterC.sks. Resize these scenes to 900 wide by 600 tall, the same as EncounterA. You can fill these encounters with Bees, Blades, Coins, and Bats—have fun! Make sure to assign the custom class attribute to the sprites that you drag into the scene editor.

For inspiration, here is my EncounterB.sks:

Here is my EncounterC.sks:

For perfect alignment with the ground, place your Blade sprites at -224 on the Y-axis.

Updating the...

Adding the Power-up Star at random places

We still need to add the Power-up Star into the world. We can randomly spawn a Star every ten encounters to add some extra excitement. Follow these steps to add the Star logic:

1. Add a new instance of the Star class as a constant on the GameScene class:

           let powerUpStar = Star() 

2. Anywhere inside the GameScene didMove function, add the Star as a child of the GameScene and position it:

           // Place the star out of the way for now: 
           self.addChild(powerUpStar) 
           powerUpStar.position = CGPoint(x: -2000, y: -2000) 

3. Inside the GameScene didSimulatePhysics function, update your new encounter code as follows (the new code is in bold):

           // Check to see if we should set a new encounter: 
           if player.position.x > nextEncounterSpawnPosition { 
               encounterManager.placeNextEncounter( 
                   currentXPos: nextEncounterSpawnPosition) 
               nextEncounterSpawnPosition += 1200 
        
               // Each encounter...

Turning bronze coins into gold coins

You may notice that your gold coins in the scene editor show up as bronze coins in the game. This is because the Coin class defaults to using the bronze texture and value. We will specify our gold coins by setting their name attribute to gold in the scene editor and then checking for this name in the Coin init function. Follow these steps to implement golden coins:

1. Open your encounters in the scene editor, select your gold coins, and use the Attributes inspector to set the name value of each node to gold, as shown here:

   

2. We can easily loop through all nodes with a certain name. We will use this functionality to run the Coin class's turnToGold function on any node with the name gold. Open EncounterManager and add the following code in the init function, at the bottom of the encounter's for loop (the new code is in bold):

           // Save initial sprite positions for this encounter: 
           saveSpritePositions(node: encounterNode) 
           // Turn golden coins...

Summary

Great job—we have covered a lot of ground in this chapter. You learned about Xcode's new scene editor, used the scene editor to lay out sprites with custom classes, and interpreted the scene data to spawn game objects in our game world. Then, you created a system to loop encounters for our endless flyer game.

Congratulate yourself; the encounter system you built in this chapter is the most complex system in our game. You are officially in a great position to finish your first SpriteKit game!

Next, we will look at creating custom events when game objects collide. We will add health, damage, coin pick-up, invincibility, and more in Chapter 7, Implementing Collision Events.