用ARKit做碰撞檢測，其實也就是做3D碰撞檢測。3D碰撞檢測需要涉及到比較復雜的數學知識，還好SceneKit給我們提供了很多方便的方法來實現3D碰撞檢測。接下來，我們用ARKit來實現一個簡單的3D碰撞檢測

一、創建工程

*.png

我們選擇用Swift語言

二、將需要的模型文件拖進工程

**.png

模型放在art.scnassets文件夾

三、創建egg節點

創建egg節點，給節點添加物理屬性

    override func viewDidLoad() {
        super.viewDidLoad()
        sceneView.delegate = self
        sceneView.showsStatistics = true
        let scene = SCNScene(named: "art.scnassets/egg.scn")!
        let eggNode = scene.rootNode.childNode(withName: "egg", recursively: false)
        //節點位置
        eggNode?.position = SCNVector3(5,0,-40)
        //創建physicBody
        let body = SCNPhysicsBody(type: .static, shape: SCNPhysicsShape(node: eggNode!, options: nil))
        //是否受重力影響
        body.isAffectedByGravity = false
        eggNode?.physicsBody = body
        //物理特性
        eggNode?.physicsBody?.categoryBitMask = 3
        eggNode?.physicsBody?.contactTestBitMask = 2
        sceneView.scene.rootNode.addChildNode(eggNode!)
        sceneView.debugOptions = [ARSCNDebugOptions.showFeaturePoints,ARSCNDebugOptions.showWorldOrigin]
      //設置 SCNPhysicsContactDelegate
        sceneView.scene.physicsWorld.contactDelegate = self
    }

四、點擊屏幕創建子彈節點

  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        
        let geometry = SCNSphere(radius: 0.1)
        geometry.firstMaterial?.diffuse.contents = UIColor.red
        let buttleNode = SCNNode(geometry: geometry)
        
        guard let sceneView = self.view as? ARSCNView else {
            return
        }
        guard let pointView = sceneView.pointOfView else {
            return
        }
        let transform = pointView.transform
        //子彈射向的位置
        buttleNode.position = SCNVector3((-transform.m31-transform.m41),(-transform.m32-transform.m42),(-transform.m33-transform.m43))
        //創建鋼體
        let body = SCNPhysicsBody(type: .dynamic, shape: SCNPhysicsShape(node: buttleNode, options: nil))
        //是否受重力影響
        body.isAffectedByGravity = false
        
        buttleNode.physicsBody = body
      //子彈飛行速度
        buttleNode.physicsBody?.applyForce(SCNVector3( (-transform.m31) * 50,(-      transform.m32) * 50,(-transform.m33) * 50), asImpulse: true)
        buttleNode.physicsBody?.categoryBitMask = 2
        buttleNode.physicsBody?.contactTestBitMask = 3
    sceneView.scene.rootNode.addChildNode(buttleNode)
        
    }

五、實現SCNPhysicsContactDelegate

var Target: SCNNode? //碰撞之後的結果

//    當被添加了 physicsBody 的節點 相互碰觸的時候 調用這個方法
func physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact){
        let nodeA = contact.nodeA  //第一次子彈
        let nodeB = contact.nodeB //第二個蛋
        if nodeA.physicsBody?.contactTestBitMask == 2 {
            Target = nodeA //沒射中 留下的是子彈 
        }else if nodeB.physicsBody?.contactTestBitMask == 3{
            Target = nodeB //射中了 留下的是蛋
        }

    //這個效果通過創建scnp文件選擇
    let confetti = SCNParticleSystem(named: "art.scnassets/smoke.scnp", inDirectory: nil)

如下圖：

***.png

        confetti?.loops = false
        confetti?.particleLifeSpan = 4
        confetti?.emitterShape = Target?.geometry
        
        let confetNode = SCNNode()
        confetNode.addParticleSystem(confetti!) //節點上添加的特效
        confetNode.position = contact.contactPoint //兩個節點碰撞后作用的地方
        sceneView.scene.rootNode.addChildNode(confetNode)
        Target?.removeFromParentNode()
    }

六、運行

好了，一個ARKit碰撞射擊游戲就這么簡單的完成，有沒有很happy
效果圖：
撞擊前是一個完整的蛋

i.png

撞擊后變為一縷青煙

ii.png