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Develop a 3D Skee Ball Game With Unity

Final product image
What You'll Be Creating


In this tutorial, you'll learn how to create a mobile 3D game using C# and Unity. The objective of the game is to throw the ball into the holes using the touch screen.

You will learn about the following aspects of Unity game development in this tutorial:

  • importing 3D models
  • swipe gesture controls
  • class communication
  • physics forces
  • trigger colliders

1. Create a New Unity Project

Open Unity and select New Project from the File menu to open the new project dialog. Tell Unity where you want to save the project and set the Set up defaults for: menu to 3D.

2. Build Settings

In the next step, you're presented with Unity's user interface. Set the project up for mobile development by choosing Build Settings from the File menu and selecting your platform of choice.

3. Devices

The first thing we need to do after selecting the target platform is choosing the size of the artwork we'll be using in the game. This will help us select a proper size for the 3D textures and 2D GUI without making the artwork blurry or use textures that are too large for the target device. For example, the artwork needs to have a higher resolution if you're targeting an iPad with a retina display than a Lumia 520.


  • iPad without Retina: 1024px x 768px
  • iPad with Retina: 2048px x 1536px
  • 3.5" iPhone/iPod Touch without Retina: 320px x 480px
  • 3.5" iPhone/iPod with Retina: 960px x 640px
  • 4" iPhone/iPod Touch: 1136px x 640px


Because Android is an open platform, there's a wide range of devices, screen resolutions, and pixel densities. A few of the more common ones are listed below.

  • Asus Nexus 7 Tablet: 800px x 1280px, 216 ppi
  • Motorola Droid X: 854px x 480px, 228 ppi
  • Samsung Galaxy SIII: 720px x 1280px, 306 ppi

Windows Phone & BlackBerry

  • Blackberry Z10: 720px x 1280px, 355 ppi
  • Nokia Lumia 520: 400px x 800px, 233 ppi
  • Nokia Lumia 1520: 1080px x 1920px, 367 ppi

Note that the code we'll write in this tutorial can be used to target any of the platforms.

4. Export Graphics

Depending on the devices you're targeting, you may need to convert the artwork to the recommended size and pixel density. You can do this in your favorite image editor. I've used the Adjust Size... function under the Tools menu in OS X's Preview application.

5. Unity User Interface

Before we get started, make sure the 2D button in the Scene panel is not highlighted. You can also modify the resolution that's being displayed in the Game panel.

You're then presented with the workspace panels, which we'll also use in this tutorial. Take a moment to look at the main interface panels, such as the Scene, Game, Hierarchy, Project, Assets, and Inspector. We'll use them frequently in this tutorial.

6. Game Interface

The user interface of the game is straightforward. The screenshot below gives you an idea of the artwork we'll be using and how the final user interface will end up looking. You can find the artwork and additional resources in the tutorial's source files on GitHub.

7. Programming Language

You can use one of three programming languages when using Unity, C#UnityScript, a variation of JavaScript, and Boo. Each programming language has its pros and cons, and it's up to you to decide which one you prefer. My personal preference goes to the C# programming language so that's the language I'll be using in this tutorial.

If you decide to use another programming language, then make sure to take a look at Unity's Script Reference for examples.

8. Sound Effects

I'll use a number of sounds to improve the audial experience of the game. The sound effects used in this tutorial were obtained from PlayOnLoop and Freesound.

9. 3D Models

To create the game, we first need to get a few 3D models. I recommend 3docean for high quality models and textures, but if you're testing or learning, then free models will work just as fine. The models in this tutorial were downloaded from SketchUp 3D Warehouse where you can find a wide variety of 3D models.

Because Unity doesn't recognize the SketchUp file format, we need to convert it to something Unity can import. We first need to download the free version of SketchUp, which is called SketchUp Make.

Open the 3D model in SketchUp Make, select Export > 3D Model from the File menu, and choose Collada (*.dae). Choose a name and location, and click Save. This will create a file and a folder for the 3D model. The file contains the data for the 3D object while the folder contains the model's textures. In the next step, we'll import the model into Unity.

10. Import Assets

Before we start coding, we need to add the assets to the Unity project. You can do this one of several ways:

  • select Import New Asset from the Assets menu
  • drag and drop the assets in the project window
  • add the items to the project's assets folder

After completing this step, you should see the assets in your project's Assets folder in the Project panel.

11. Setup Camera

Before we continue, let's position the main camera to create the view we want. Select the main camera from the Hierarchy panel and adjust the Transform values in the Inspector to match the ones shown below.

Don't worry if you don't see any changes. We haven't created anything for the camera to see yet.

12. Adding Light

For our objects to be visible in the 3D world, we need to add light to the scene. Select Create Other from the GameObject menu and select Directional Light. This will create an object that produces a beam of light. Change its Transform values as shown in the following screenshot to make it illuminate the area.

The light should be visible on the scene as shown in the following screenshot.

13. Add Alley Bowlers

The alley bowlers are the main components of the game's scene. The player will use the touch screen to throw a ball, aiming for one of the holes.

The model used in this tutorial was downloaded and imported using the method described in Step 9.

Even though we'll add three models to the scene, the play will only interact with the one in the center. Drag and drop an instance of the model on the Scene or Hierarchy panel and change its Transform values to the ones shown in the screenshot below.

Use the same method to add the other two instances or duplicate the first instance by pressing Command-D. Use the Transform Tools to position them as shown below.

14. Create Colliders

With the main alley in place, it's time to add colliders to the model to help us move the ball across its surface. Since this is a complex model with lots of groups and polygons, it would take us a long time identifying the various shapes and adding a collider to each of them. To make this step easier, we'll use a third-party script to automatically create a collider that fits our model.

The script will add a new menu item named Wizards to the Unity menu. Select the model to which you want to add the collider and select Add Mesh Colliders from the Wizards menu. This will bring up the following window.

Click Add Colliders in the bottom right to add colliders to the model. This will create a Mesh Collider for every group or object of the model. You can verify this by expanding the ballbowler model in the Hierarchy and selecting an item.

15. Spotlights

We've added a light source to our 3D world, but we need a bit more light to make the scene more interesting. We do this by adding a number of spotlights.

Select Create Other from the GameObject menu and select Spotlight. This will create an object that produces a beam of light directed to one spot. The first spotlight we add needs to illuminate the holes. Change its Transform values as shown in the following screenshot.

Add a second spotlight using the following transform values.

16. Ball

The ball is the most important component of the game. The player will use the touch screen to try and get the ball in one of the holes.

The ball is going to be a simple Sphere primitive. Select Create Other > Sphere from the GameObject menu to create the primitive and modify the Transform values in the Inspector as shown below.

We'll convert the ball to a Prefab later as it will help us create instances of it in code. But first, let's add a RigidBody to it.

17. Ball RigidBody

To detect a collision with the ball, we need to attach a RigidBody to it. To add one, select Add Component from the Inspector panel, followed by Physics > RigidBody. You can leave the settings at their defaults.

18. Ball Sensors

We need to detect when the ball falls into a hole. We'll use Trigger Colliders for this purpose. A trigger collider is a physics object that detects a collision with another object without reacting physically. This will help us detect when the ball enters the hole without making it bounce back.

Since we don't need an actual model or 2D graphic to do this, we'll create an Empty GameObject. Select GameObject > Create Empty from the menu bar to create it. Click the Add Component button in the Inspector and choose Physics > Box Collider.

This will add a box collider to the game object. Repeat this process for every hole and make sure to check the Trigger checkbox.

Position the colliders as shown in the screenshot below.

19. Scoreboard

To display the game's scoreboard, we'll use Unity's GUI Textures. By default, images imported to the Assets folder are converted to Texture instances that can be applied to 3D objects. We need to change these Texture instances to GUI Texture instances for the images we want to use in the game's user interface.

Select the image you want to convert in the Assets panel and open the Inspector. Select GUI from the Texture Type menu.

You can now drag and drop the image to the Scene. The image will always appear in front of every object on the stage and will be treated as a 2D element.

20. Scoreboard Text

Inside the scoreboard GUI element, we'll display numbers indicating the player's score and the number of balls the player has left.

Select Create Other > GUI Text from the GameObject menu to create a text object, place it at the center of the GUI element, and change the text in the Hierarchy panel to 00. Follow the same process for the balls text to complete the scoreboard.

21. Adding Scripts

It's time to write some code. With the user interface in place, we can start writing the necessary code to add interaction to the game. We do this by means of scripts, which can be attached to game objects. Follow the next steps to learn how to add interaction to the level we've just created.

22. ThrowBall Class

Step 1: Declaring Variables

We'll start by creating the class that handles most of the game mechanics. Select the main camera, click the Add Component button in the Inspector panel, and choose New Script. Name the script ThrowBall and don't forget to change the language to C#. Open the newly created file and add the following code snippet.

We start by creating a number of variables that we'll use in the game. Let's take a look at each one.

  • throwSpeed: the initial velocity of the ball when placed on the alley
  • ballReference: a reference to the ball prefab, set in the inspector
  • startPos: start position of the first touch, used to detect a swipe gesture
  • endPos: end position of the touch
  • minDistance: minimum movement needed for the finger to be considered a swipe
  • ballPos: initial ball position
  • ballOnStage: true when a ball is currently on the alley, to prevent multiple shots at the same time
  • ballsLeft: the number of remaining balls
  • ballsTextReference: reference to the balls textfield, set in the inspector
  • throwSound: reference to the sound played when the ball is thrown, set in the inspector

Step 2: Detecting Touches

The following code snippet shows the beginning of the Update method. This method detects if the user is touching the screen.

We check the touchCount property of the Input class to get the current number of touches on the screen. If touchCount is greater than 0, we keep a reference to the first Touch object. We'll use this object later.

Step 3: Detecting a Swipe

With a reference to the Touch object, we have access to its phase property, which helps us determine if the touch has started, moved, or ended.

Because we need a starting point to detect a swipe gesture, we need access to the starting point of the Touch object, which we have access to when the Touch object's phase is equal to TouchPhase.Began. The position of the Touch object is stored in its position property.

We have access to the endpoint of the gesture by accessing the Touch object's position property when its phase property is equal to TouchPhase.Ended.

Now that we have the coordinates of the start and endpoint of the touch, we can calculate the distance and check whether it's a valid swipe gesture by comparing it with the value stored in the minDistance object.

We also inspect the value of ballOnStage to check if a ball is already on the scene and we make sure that the player has enough balls left to continue playing. The number of balls left is stored in the ballsLeft variable.

Step 4: Detecting the Screen Zone

Screen zones are created to calculate where the horizontal position of the ball is going to be when the ball is created. We do this to have control over the ball's position and it tells us where the ball is going to end and prevent throwing it out of bounds. We divide the screen in three parts as you can see below.

The math we use is quite simple as you can see in the code block below. We divide the screen in three equal parts and check which part contains the user's touch.

After detecting the correct screen zone, we calculate a random position between the start and end of the zone and assign that position to the ballPos variable.

Step 5: Throwing the Ball

After determining the starting position of the ball, we create a new GameObject instance using the Instantiate method, passing in the ballReference and ballPos variables.

With the ball on the scene, we add a force to make it move through the correct alley. We do this by invoking the AddForce method on the ball's rigidbody property, passing in the throwSpeed variable we declared earlier.

Step 6: Playing a Sound Effect

We play a sound effect when the ball is thrown in the alley. The next line of code takes care of that. For this tot work, remember to set the throwSound variable in the Inspector.

Step 7: Resetting the Swipe Variables

After throwing the ball, we need to reset the variables that detect the player's touches. Not doing this would result in multiple swipes being detected. We also set the ballOnStage variable to true, preventing that another ball is thrown at the same time.

This completes the ThrowBall class. The implementation of the class should look like th one shown below.

23. BallSensor Class

The following script contains the implementation of the BallSensor class and is attached to the ball sensors, handling any collisions with the ball sensors.

Step 1: Declaring Variables

We start by declaring a variable named sensorValue, which stores the number of points the ball sensor will add to the score. Because the ball sensors are all the same prefab, we declare this variable as public. This will allow us to set this value in the editor using the Inspector.

The other two variables store references to the score and alert game objects, which we also set in Unity's InspectorThese references will be used to increase the score and display the alert when the game ends.

Step 2: Destroying the Ball

The OnTriggerEnter method detects when a collision has occurred and accepts the Collider object the sensor is colliding with, the ball in this case. When a collision is detected, the ball is destroyed to prevent it from bouncing and potentially falling in another hole.

Step 3: Enabling Throw

After destroying the ball, we are sure that it isn't on the alley anymore. This means we can throw another ball without causing an unwanted behavior. The following line of code communicates with the ThrowBall class and gets the ballOnStage variable, setting it to false.

Let's take a closer look at how we access a variable declared in another class. As you can tell by now, one way to access a variable or object declared outside of the current class is to set a reference variable using public or [SerializeField], and then use the Inspector to give it a value.

The public keyword plays an important role in this. Using it makes the variable not only accessible from the Inspector, but also through code. To do this, we first need access to the GameObject that has the Script Component attached to it, which is the Main Camera in this case.

There is only one camera in this game, which makes things easier. We can get a reference to the main camera through Camera.main. Using GetComponent we get the script attached to the camera, using the name of the class. We then have access to the public variable named ballOnStage.

Step 4: Changing the Score

The following code block updates the score, using the reference we declared earlier.

We convert the value stored in scoreReference to an integer and add it to the value stored in sensorValue. We convert the result to a string and assign it to the text property of scoreReference.

Step 5: Updating the Remaining Balls

In this step, we decrease the number of remaining balls. We use the method described in Step 3 to access the ballsLeft and ballsTextReference variables of the ThrowBall class.

We decrement the value stored in ballsLeft and update the text property of ballsTextReference.

Step 6: Checking for Game Over

The game is over when the player runs out of available shots. The next lines of code check if the ballsLeft variable is equal to 0 and create an alert if true. We then call the Invoke method to invoke the Reload method, which restarts the game by reloading the current scene.

The second parameter of the Invoke method defines the delay with which the Reload method will be invoked. We do this to give the player some time before we start a new game.

Step 7: Reloading the Game

This is the last part of the BallSensor class. In the Reload method, we call LoadLevel on the Application class and reload the current level, resetting every object and variable to its initial state.

This is what the class looks like when finished.

24. Testing

It's time to test the game. Press Command-P to play the game in Unity. If everything works as expected, then you're ready for the final steps.

25. Player Settings

When you're happy with your game, it's time to select Build Settings from the File menu and click the Player Settings button. This should bring up the Player Settings in the Inspector panel where you can set the parameters for your application.

These settings are application specific data that includes the creator or company, app resolution and display mode, rendering mode (CPU, GPU), device OS compatibility, etc. Configure the settings according to the devices you're targeting and the store or market where you plan to publish the app.

26. Icons and Splash Images

Using the graphics you created earlier, you can now create a nice icon and a splash image for your game. Unity shows you the required sizes, which depend on the platform you're building for.

27. Build and Play

Once your project is properly configured, it's time to revisit the Build Settings and click the Build Button. That's all it takes to build your game for testing and/or distribution.


In this tutorial, we've learned how to use physics forces, swipe gestures, class communication, and other aspects of game development in Unity. I encourage you to experiment with the result and customize the game to make it your own. I hope you liked this tutorial and found it helpful.

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