命中检测过程是指在视图上去一点，找出3D中的哪个对象位于视图上这个点的下方。实际上就是要回答：我点了谁？

在对一个SceneKit视图进行命中检测时，会得到一个SCNHitTestResult对象的数组，其中描述了找到的对象，以及该对象的相关信息。

下面这段代码可以让你点击的地方短暂的发亮一下：

import UIKit
import SceneKit
import SpriteKit

class SceneKitViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let sceneView = self.view as! SCNView
        sceneView.backgroundColor = UIColor.grayColor()
        //sceneView.allowsCameraControl = true
        // 添加场景
        let sceneOne = SCNScene()
        sceneView.scene = sceneOne
        // 添加照相机 并指明水平和垂直视角都是45度
        let cameraOne = SCNCamera()
        cameraOne.xFov = 45
        cameraOne.yFov = 45
        // 将照相机附加到节点
        let cameraNode = SCNNode()
        cameraNode.camera = cameraOne
        cameraNode.position = SCNVector3(0,0,20)
        sceneOne.rootNode.addChildNode(cameraNode)
        // 添加3D对象
         let capsuleOne = SCNCapsule(capRadius: 2.5,height: 10)
        let capsuleNodeOne = SCNNode(geometry: capsuleOne)
        capsuleNodeOne.position = SCNVector3(0,0)
        sceneOne.rootNode.addChildNode(capsuleNodeOne)
        // 添加环境光源
        let ambientLight = SCNLight()
        ambientLight.type = SCNLightTypeAmbient
        ambientLight.color = UIColor(white: 0.25,alpha: 1.0)
        let ambientNodeOne = SCNNode()
        ambientNodeOne.light = ambientLight
        sceneOne.rootNode.addChildNode(ambientNodeOne)
        // 添加泛光源
        let omniLight = SCNLight()
        omniLight.type = SCNLightTypeOmni
        omniLight.color = UIColor(white:1.0,alpha: 1.0)
        let omniNodeOne = SCNNode()
        omniNodeOne.light = omniLight
        omniNodeOne.position = SCNVector3(-5,8,5)
        sceneOne.rootNode.addChildNode(omniNodeOne)
        // 为场景中的内容实现动画
        let moveUpAndDownAnimation = CABasicAnimation(keyPath: "position")
        moveUpAndDownAnimation.byValue = NSValue(SCNVector3:SCNVector3(0,5,0))
        // 在最后加速和减速，而不是机械弹跳
        moveUpAndDownAnimation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaSEOut)
        // 在末端自动返回
        moveUpAndDownAnimation.autoreverses = true
        // 动画无限次循环
        moveUpAndDownAnimation.repeatCount = Float.infinity
        moveUpAndDownAnimation.duration = 2
        // 添加到一个节点
        capsuleNodeOne.addAnimation(moveUpAndDownAnimation,forKey: "upAndDown")
        // 创建文本几何体
        let text3D = SCNText(string: "BlaBlaBla",extrusionDepth: 0.3)
        text3D.font = UIFont.systemFontOfSize(2)
        let textNode = SCNNode(geometry: text3D)
        textNode.position = SCNVector3(-5,6,0)
        capsuleNodeOne.addChildNode(textNode)
        // 合并动画
        let rotateAnimation = CABasicAnimation(keyPath: "eulerAngles")
        rotateAnimation.byValue = NSValue(SCNVector3: SCNVector3(x: Float(0),y: Float(M_PI*2),z: Float(0)))
        rotateAnimation.repeatCount = Float.infinity
        rotateAnimation.duration = 4
        textNode.addAnimation(rotateAnimation,forKey: "rotation")
        // 质感和纹理
        let redMetallicMaterial = SCNMaterial()
        redMetallicMaterial.diffuse.contents = UIColor.grayColor()
        redMetallicMaterial.specular.contents = UIColor.whiteColor()
        redMetallicMaterial.shininess = 1
        capsuleOne.materials = [redMetallicMaterial]
        // 文字纹理
        let noiseTexture = SKTexture(noiseWithSmoothness:0.25,size:CGSize(width: 512,height: 512),grayscale:true)
        let noiseMaterial = SCNMaterial()
        noiseMaterial.diffuse.contents = noiseTexture
        text3D.materials = [noiseMaterial]
        // 法向贴图
        let noiseNormalMapTexture = noiseTexture.textureByGeneratingNormalMapWithSmoothness(0.1,contrast: 1)
        redMetallicMaterial.normal.contents = noiseNormalMapTexture
        // 命中检测
        let tapRecognizerOne = UITapGestureRecognizer(target: self,action: "tapped:")
        sceneView.addGestureRecognizer(tapRecognizerOne)
        // 启动用户交互
        sceneView.userInteractionEnabled = true

    }

    func tapped(tapRecognizer:UITapGestureRecognizer){
        if tapRecognizer.state == UIGestureRecognizerState.Ended{
            let sceneView = self.view as! SCNView
            let hits = sceneView.hitTest(tapRecognizer.locationInView(tapRecognizer.view),options: nil) as [SCNHitTestResult]

            for hit in hits {
                if let theMaterial = (hit.node.geometry?.materials[0]) as SCNMaterial? {
                    let highLightAnimation = CABasicAnimation(keyPath: "contents")
                    highLightAnimation.fromValue = UIColor.blackColor()
                    highLightAnimation.toValue = UIColor.yellowColor()
                    highLightAnimation.autoreverses = true
                    highLightAnimation.repeatCount = 0
                    highLightAnimation.duration = 0.3

                    theMaterial.emission.addAnimation(highLightAnimation,forKey: "highLight")
                }
            }
        }
    }


}