ARKit - 与现实世界物体的碰撞

Question

我需要使用 ARKit 检测虚拟对象何时与现实世界对象接触。

有什么办法可以查到吗？

Answer 1

首先你需要创建一个符合OptionSet协议并且具有bitset类型的属性的碰撞类别结构体：

import ARKit

struct Category: OptionSet {

    let rawValue: Int
    
    static let sphereCategory = Category(rawValue: 1 << 0)
    static let targetCategory = Category(rawValue: 1 << 1)
}

然后在生命周期方法中设置一个physics delegate 到SCNPhysicsContactDelegate 协议：

class ViewController: UIViewController, SCNPhysicsContactDelegate {

    @IBOutlet var sceneView: ARSCNView!

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        sceneView.scene = SCNScene()
        sceneView.scene.physicsWorld.contactDelegate = self

        let config = ARWorldTrackingConfiguration()
        config.planeDetection = [.horizontal]
        sceneView.session.run(config)
    }
}

SCNPhysicsContactDelegate 包含 3 个可选的physicsWorld() 方法（稍后我们将使用第一个）：

public protocol SCNPhysicsContactDelegate: NSObjectProtocol {
        
    optional func physicsWorld(_ world: SCNPhysicsWorld, 
                      didBegin contact: SCNPhysicsContact)

    optional func physicsWorld(_ world: SCNPhysicsWorld, 
                     didUpdate contact: SCNPhysicsContact)

    optional func physicsWorld(_ world: SCNPhysicsWorld, 
                        didEnd contact: SCNPhysicsContact)
}

在此之后为球体对撞机定义categoryBitMask 和collisionBitMask：

fileprivate func createSphere() -> SCNNode {

    var sphere = SCNNode()
    sphere.geometry = SCNSphere(radius: 0.1)

    sphere.physicsBody =  .init(type: .kinematic, 
                               shape: .init(geometry: sphere.geometry!, 
                                             options: nil))

    sphere.physicsBody?.isAffectedByGravity = true

    sphere.physicsBody?.categoryBitMask = Category.sphereCategory.rawValue
    sphere.physicsBody?.collisionBitMask = Category.targetCategory.rawValue
    sphere.physicsBody?.contactTestBitMask = Category.targetCategory.rawValue

    return sphere
}

...并以相反的顺序为现实世界检测到的平面定义位掩码：

fileprivate func visualizeDetectedPlane() -> SCNNode {

    var plane = SCNNode()
    plane.geometry = SCNPlane(width: 0.7, height: 0.7)

    plane.physicsBody =  .init(type: .kinematic, 
                              shape: .init(geometry: plane.geometry!, 
                                            options: nil))

    plane.physicsBody?.isAffectedByGravity = false

    plane.physicsBody?.categoryBitMask = Category.targetCategory.rawValue
    plane.physicsBody?.collisionBitMask = Category.sphereCategory.rawValue
    plane.physicsBody?.contactTestBitMask = Category.sphereCategory.rawValue

    return plane
}

只有当您将 SCNPlanes 添加到实际检测到的平面并将 SCNSphere 添加到您的 SCNScene 时，您才能使用 physicsWorld(_:didBegin:) 实例方法来检测碰撞：

func physicsWorld(_ world: SCNPhysicsWorld, 
         didBegin contact: SCNPhysicsContact) {

    if contact.nodeA.physicsBody?.categoryBitMask == 
                                          Category.targetCategory.rawValue |
       contact.nodeB.physicsBody?.categoryBitMask == 
                                          Category.targetCategory.rawValue {

        print("BOOM!")
    }
}