一、与SceneKit的对比

和SceneKit项目结构图一样，SpriteKit项目中多了一个Scene.sks的文件，这个文件是SpriteKit的场景文件，该文件只能看到2D平面。

二、效果

• 运行时，看到界面上只有相机画面。此时点击屏幕，就会出现一棵小松树，每多点一次，就会多一棵小松树。
• 不管你怎么移动手机，小松树始终朝向你，当你有多棵小松树时，它们之间始终保持一定的距离。
• SpriteKit会把2D图像以漂浮的方式放入3D空间中，就类似一个广告牌放置在某处，当你移动设备时，这个广告牌始终朝向你。

三、创建AR项目

• Content Technology：SpriteKit渲染框架
• 代码解析：

#import "ViewController.h"
#import "Scene.h"

@interface ViewController () <ARSKViewDelegate>

@property (nonatomic, strong) IBOutlet ARSKView *sceneView;

@end


@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // Set the view's delegate
    //设置视图代理
    self.sceneView.delegate = self;

    // Show statistics such as fps and node count
    //显示FPS信息
    self.sceneView.showsFPS = YES;
    //显示节点数
    self.sceneView.showsNodeCount = YES;

    // Load the SKScene from 'Scene.sks'
    //加载资源文件
    Scene *scene = (Scene *)[SKScene nodeWithFileNamed:@"Scene"];

    // Present the scene
    //在视图中替换掉当前的场景，并且显示刚才加载的场景
    [self.sceneView presentScene:scene];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    // Create a session configuration
    //创建会话配置对象
    ARWorldTrackingConfiguration *configuration = [ARWorldTrackingConfiguration new];

    // Run the view's session
    //运行当前视图自带的会话
    [self.sceneView.session runWithConfiguration:configuration];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    // Pause the view's session
    //停止运行当前视图自带的会话
    [self.sceneView.session pause];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - ARSKViewDelegate

- (SKNode *)view:(ARSKView *)view nodeForAnchor:(ARAnchor *)anchor {
    // Create and configure a node for the anchor added to the view's session.
    //创建并设置一个节点，并且把它放到会话给定的锚点(位置)上
    SKLabelNode *labelNode = [SKLabelNode labelNodeWithText:@"👾"];
    labelNode.horizontalAlignmentMode = SKLabelHorizontalAlignmentModeCenter;
    labelNode.verticalAlignmentMode = SKLabelVerticalAlignmentModeCenter;
    return labelNode;
}   

#import "Scene.h"

@implementation Scene

- (void)didMoveToView:(SKView *)view {
    // Setup your scene here
}

- (void)update:(CFTimeInterval)currentTime {
    // Called before each frame is rendered
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    if (![self.view isKindOfClass:[ARSKView class]]) {
        return;
    }

    ARSKView *sceneView = (ARSKView *)self.view;
    ARFrame *currentFrame = [sceneView.session currentFrame];

    // Create anchor using the camera's current position
    //使用摄像头当前的位置创建一个锚点
    if (currentFrame) {

        // Create a transform with a translation of 0.2 meters in front of the camera
        //创建一个向摄像头前方平移0.2m的转换
        matrix_float4x4 translation = matrix_identity_float4x4;
        translation.columns[3].z = -0.2;

        //使用当前帧中摄像头的位置进行转换，转换后得到一个矩阵
        matrix_float4x4 transform = matrix_multiply(currentFrame.camera.transform, translation);

        // Add a new anchor to the session
        //新建一个锚点并添加到会话中
        ARAnchor *anchor = [[ARAnchor alloc] initWithTransform:transform];
        [sceneView.session addAnchor:anchor];
    }
}   

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