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Seals are the big bad in the Peeved Penguins world. The goal is to crush all of them! You catapult penguins into their to try and crush them.

Your next step is to create the Seal and Penguin objects.

The Penguin

The penguins and seals will need get their own SKS files as they will be reusable game objects in the game scene. You will be adding them in both the Scene Editor and directly in your code.

Create a new SKS file (File > New > File > SpriteKit Scene), set Name to Penguin.sks.

Drag the flyingpenguin.png asset into scene from the Media Library. Set the Scene Size to Custom - (25,25), this matches the Size of the flyingpenguin.png.

Snap the penguin to the center of the scene.

Penguin Scene

The penguin is nearly ready for action, this will be a physics based game so the penguin will need to be physics enabled. If you look at the shape of the penguin it's nearly a ball.... The perfect physics projectile body :]

Enabling physics

Select the penguin and scroll through the Attributes inspector, until you find the Physics Definition section.

Set Body Type to Bounding Circle, this will open up the additional physics attributes to work with. Set Friction to 0.6, although the penguin will be smashing into ice blocks you want to ensure it doesn't slide around too much. There is a fine balance between realism and fun. Set Mass to 0.50 as the penguin should act as more of a cannon ball than a fluffy ball of fur. Set Category Mask to 1 as this will be the first physics group in the simulation.

Penguin physics definition

For additional information relating to Physics Masks please see @TODO BE BINCE TO HAVE A COOL PHYSICS MASK PLAYGROUND TO LINK TO

You may wonder, where did these values come from? Did I run the simulation in my head? No...

Trial and error, the key to a fun physics simulation is lots of tweaking. Don't worry it's a normal part of game development. Getting the balance right can be the difference between great and mediocre.

Accessing the penguin

There is one not so obvious issue you need to deal with. If you drag the penguin into the GameScene an SKReferenceNode will be created, it's important to note this is a reference to the Penguin.sks scene, NOT the penguin SKSpriteNode. However, you need to be able to access the penguin's physics body to apply physics forces to it.

Thankfully we've already created a handy sub-class of SKReferenceNode called MSReferenceNode that will let you access the penguin SKSpriteNode inside the penguin scene.

Download MSReferenceNode.swift and add it to your project. As always have a sneaky peek at the code. You will be making use of the class in later chapters.

It's important to set the Name of the SKSpriteNode in the scene you require access to, in this case it is the penguin.

Click on the penguin and set Name property to avatar Penguin node namde

Great job, time to add those evil seals! The process of creating the seal will be nearly identical to that of the Penguin.

The seal

See how far you can get on your own.

Create a new SKS file (File > New > File > SpriteKit Scene) and name it Seal.sks.

Drag in the seal.png asset to the scene. Select the scene and Size to Custom - (27,25). Set Anchor Point to (0,0)

Enabling physics

It's often handy to think about your game physics in real terms, imagine the seal will act like a pin in ten-pin Bowling and the penguin will act as the bowling ball.

Select the penguin and scroll through the Attributes inspector, until you find the Physics Definition section.

Set Body Type to Bounding Circle, this will open up the additional physics attributes to work with. Set Category Mask to 2 as this will be the second physics group in the simulation. Set Contact Mask to 1 as you want to be notified in code when a seal is involved in a collision

Seal physics definition

That's it! You now have all the reusable game objects ready to add to your game scene.


You learnt to:

  • Create reusable game objects
  • Enable physics bodies and tweak properties
  • Think about your game physics simulation in real world terms

In the next chapter you will be building the first thing the player typically sees in any game, the main menu.


If you have feedback on this tutorial or find any mistakes, please open issues on the GitHub Repository.

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