SceneKit Tutorial Part 1 - Create a SceneKit Project

In Xcode 6 Beta releases, Apple make us develop 3D games more smoothly on iOS8 by using SceneKit. SceneKit is much easier to make 3D effects like lights, shadows and textures. And it also has build-in actions and physical behaviors. This tutorial is a practical guide that show you how to make your game step by step using Xcode 6.

There is a quick start that you can use in Xcode 6.  After you've opened Xcode 6, click File from menu and go to New and then select Project to create a new project, you will see the following dialog box:

The Wizard to Create a New Project in Xcode 6

Select Game from the board and click Next. You will see the parameters for the project:

The Properties of the Project

Pay attention that you can choose SceneKit from Game Technology drop down list and Swift in Language list. After input your Project Name, Organization Name and Organization Identifier, by clicking Next and then Create button, you will create a new project like this:

Workspace of a SceneKit Project

Above are the template code written with Swift. In this tutorial, I will use Swift for demo code. And you can find all the code of this tutorial at here.

Now the new game is ready to run without any changes to the template code! Although it is just a template, you can study and start your game from beginning. The result of the SceneKit template game looks like this:

The Snapshot When SceneKit Template Project is Running

In the running game, you will see the 3D plane is rotating and you can adjust the angle of camera. You may remember the 2D plane in Sprite Kit template project, it is upgraded!

Most of time you may want to start using SceneKit from single view project, you can create one and add SceneKit.framework from Linked Frameworks and Libraries section of project panel to use SceneKit:

Select SceneKit Framework for Single View Project

In this tutorial, I've create a single view application and I will explain SceneKit code line by line. 

The Apple's SceneKit Framework Reference gives you a good introduction to SceneKit 's key concepts like coordinate system and main classes. It will help you going through the code here.

There are some other knowledges you need to know that may not mentioned in Apple's guide. Like SpriteKit, SceneKit also has the concept like scene(SCNScene) and node(SCNNode), and they are in a hierarchy relationship. Where SCNScene has a property called root node, and every other node in the scene is one of the children or descendants of the root node(Apple calls it the root of scene graph). The "other nodes" are connected with the following types of objects: geometry, light, camera and material.

The Hierarchy of a Scene

By observing above diagram, every node and the object to be present are connected. You may imagine the object to be present is a logical concept that just contains data to describe the object. For example, the light has its power and color, the geometry has its shape. But, these objects alone cannot be presented on the scene, just like a light itself cannot shine, it still need electricity to shine and some physical objects to be illumined. So SceneKit use node(SCNNode) tied all things(Geometry, Light, Scene etc) together.

In a word, SCNNode maintain its underlying object's relationship with the scene. SCNNode tell application where to put the light and how to rotate the geometry in the scene.

All right, let's show something in our application. Suppose you have created a single view application and added the SceneKit to your project. Open the Swift source file for view controller(usually named ViewController.swift) and put the following code in viewDidLoad function:

In line 4, the code created an object of SCNView which is derived from UIView. And its size is the same with current frame. Line 5 created an object to SCNScene and put the scene into the SCNView in line 6. To show the scene, we need add the SCNView as the subview of current view.

Right now, we have nothing to show in the scene, we can run the application but you device's screen will just show white blank. To put something in it, we need to create a geometry and put it into the scene:


Well, we create a box here. To create a cubic box or a chamfered box, we use SCNBox which is derived from SCNGeometry, SceneKit also requires the box associated with a SCNNode, so we connect myBox with myBoxNode and put it to the center of the coordinate system, it will be in the center of the screen. To make the cubic box looks more like a 3D box, the code rotated the node in line 4.

It is easy to understand we use SCNVector3 to keep 3 parameters of a coordinate position. SCNVector3 is used frequently in SceneKit to specify a position in 3D space. But you may wonder why we use 4-parameter SCNVector4 here to rotate the box if you are new to 3D framework. You can understand it by breaking SCNVector4 into a point in 3D space and an angle of rotation. The line formed by the point and the center of the coordinate system is the axis for the rotation and the 4th value is the angle to rotate based on the axis.

Right now, we still cannot see anything by running the application, although we have an object in the scene. That's because we haven't put a light in the scene(we can see nothing from complete dark, right?). To put a light into the scene, create a light and a node ties the light and the scene with the code:

Here we put the light on the left-top in front of the box. So the result will looks like the left picture below:

Custom Lighting

Default Lighting

Or you can use default lightning instead of creating a light and a node for light, since SCNView has a property named autoenablesDefaultLighting, we can use the following line to use the default light(the effect is on above right picture):

myView.autoenablesDefaultLighting = true

If you use default light and custom light at the same time, the effect of default lighting will be discard. The default value of autoenablesDefaultLighting is false.

Another property of SCNView that is often used is showsStatistics, it will show statistics like fps in the bottom bar of your device(You can see the bottom bar in the application created by SceneKit template project) with this line of code:

myView.showsStatistics = true

OK, I am going to stop here today, and I will continue to write the tutorial within the series. Before I stop, I want to mention that you can use the playground introduced in Xcode 6 to play with SceneKit code. It is a very cool feature of Xcode so you can use it to see the result every line you put in playground in realtime. You can refer this link for more information to try SceneKit on playground.

Use UIWebView to Show Web Pages

If developer want to show a web page in an application, the class UIWebView is a good choice. First, we can define a property of UIWebView in view controller's implementation file:

@interface XXXViewController()

...

@property UIWebView *webview;

@end

Then initialize the UIWebView object in viewDidLoad delegate function of that view controller:

- (void)viewDidLoad

{

    [super viewDidLoad];

    ...

   _webview = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, self.size.width, self.size.height)];

    _webview.tag = 55;

    NSString *fullURL = @"https://www.facebook.com/BricKiller";

    NSURL *url = [NSURL URLWithString:fullURL];

    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];

    [_webview loadRequest:requestObj];

}

Above code initiate the UIWebView object by assigning a frame of it. The code give it a view of full screen size. The tag property of UIWebView identify the view object. It is a number and we will refer this tag number later. I also established an object of NSURL and request the content of this URL in above code.

But it hasn't been shown yet, if you want to show the web page by clicking a button, you can add the following code to button press delegate:

[self.view addSubview:_webview];

You may find an issue, if you opened the web view in your application, there is no place to close this web view and return to your original application UI. So you can add a close button on this web view by putting below code before showing the web view:

UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];

button.backgroundColor = [SKColor colorWithWhite:1.0 alpha:0.5];

[button setTitle:@"Close" forState:UIControlStateNormal];

button.frame = CGRectMake(0, _webview.frame.size.height - 100, self.size.width, 100);

[button addTarget:self action:@selector(close:) forControlEvents:UIControlEventTouchUpInside];

I set the button with white color and alpha to 0.5.  Put the button at the bottom of the web view with height 100px. And let it call close function when touch leaves the button. Next, implement close function in the same implementation file like this:

- (IBAction)close:(id)sender {

    [[self.view viewWithTag:55] removeFromSuperview];

}

Now I use the tag value to find the object of UIWebView, and then remove it from super view in close function. Here is what looks like of the running UIWebView:

Run Swift in Terminal and Script

You may have heard that the Apple's new programming language Swift can work interactively, which means when you type a line of code, you could see the result in Terminal. It's very useful when developer want to try some line of code of Swift and not for sure it is correct. Or it is a perfect way for new comer to learn the new language from beginning. How to do that? Please follow instructions here.

First, run the following command to set the path of a developer directory:

$ sudo xcode-select -switch /Applications/Xcode6-Beta5.app/Contents/Developer/

This step doesn't started a session of Swift shell, but this step is must-to-have. You may use another version of Xcode, so the developer's directory maybe different. Please check if the directory you switch to exists. It is usually with the format like /Applications/<Xcode-Version>.app/Contents/Developer/.

Remember you have to add sudo prior to the xcode-select command, otherwise you will get the error message like this:

xcode-select: error: --switch must be run as root (e.g. sudo xcode-select --switch <xcode_folder_path>).

Second, run xcrun swift to start a Swift interactive session(we don't require adding sudo anymore this time), here we run a "Hello World!" sample:

$ xcrun swift

Welcome to Swift!  Type :help for assistance.

  1> println("Hello, world!")

Hello, world!

And then type the following code to try a function which is from Apple's Swift Tour:

  2> func sumOf(numbers: Int...) -> Int { 

  3.     var sum = 0 

  4.     for number in numbers { 

  5.         sum += number 

  6.     } 

  7.     return sum 

  8. }    

  9> sumOf()

$R0: Int = 0

 10> sumOf(42, 597, 12)

$R1: Int = 651

You can see that the return values of the function is printed as the format $R<num>: <RetType> = <RetValue> with different color. That's much more clear and user friendly.

OK, that's what I show you the way to play around Swift session. An alternative way you can start the session is using lldb --repl command. The session started by the command looks the same.

You may want to see the history of the session, you can use arrow keys up and down to check previous or next Swift code line you typed. The history of Swift session of each user is kept in the file located at ~/.lldb/lldb-swift-history.

Hmm... It looks like other scripting language like Unix Shell and Python. Similar to these scripting language, Swift also works in script.

For example, create a file named swift_test like this:

#!/usr/bin/env xcrun swift

println("Hello World!")

class Shape {

    var numberOfSides = 0

    func simpleDescription() -> String {

        return "A shape with \(numberOfSides) sides."

    }

}

var shape = Shape()

shape.numberOfSides = 7

var shapeDescription = shape.simpleDescription()

println("Shape's simple description : " + shapeDescription)

Here we define a Swift class to see if it works, everything goes well it we run the script in command line:

$ ./swift_test 

Hello World!

Shape's simple description : A shape with 7 sides.

Very powerful, isn't it? It looks Swift not only works for developing App. With the library support, it could also be used for system management and automation.