swift - 在哪些情况下 ARSCNView.raycastQuery 返回 nil？

Question

在我的渲染器委托(delegate)中，我从 View 中心创建了一个光线转换查询，以跟踪估计的平面并显示一个跟随光线转换结果的 3D 指针。

通过 view.raycastQuery(from:allowing:alignment:) 完成但返回零。

我的问题是为什么？没有文档说明为什么这个函数会返回一个 nil 值。我知道光线转换结果可能是空的，但为什么不会创建查询？

func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
    guard view.session.currentFrame?.camera.trackingState == .normal else {
        return
    }
    DispatchQueue.main.async {
        let center = view.center
        DispatchQueue.global(qos: .userInitiated).async {
            if let query = view.raycastQuery(from: center, allowing: .estimatedPlane, alignment: .any) {
                let results = view.session.raycast(query)
                ...
            }
            else {
                // sometimes it gets here
            }
        }
    }
}

Answer 1

可退货ARRaycastQuery?最初是可选的
根据苹果 documentation :

raycastQuery(from:allowing:alignment:) instance method creates a ray that extends in the positive z-direction from the argument screen space point, to determine if any of the argument targets exist in the physical environment anywhere along the ray. If so, ARKit returns a 3D position where the ray intersects the target.

如果射线不与目标相交，则没有 ARRaycastQuery?目的。所以有nil .

func raycastQuery(from point: CGPoint, 
             allowing target: ARRaycastQuery.Target, 
                   alignment: ARRaycastQuery.TargetAlignment) -> ARRaycastQuery?

返回 nil 的两个可能原因是什么？ ?

没有检测到射线击中的平面

代码逻辑错误

解决方案
您的代码可能如下所示:

@IBOutlet var sceneView: ARSCNView!

@IBAction func onTap(_ sender: UIGestureRecognizer) {

    let tapLocation: CGPoint = sender.location(in: sceneView)
    let estimatedPlane: ARRaycastQuery.Target = .estimatedPlane      
    let alignment: ARRaycastQuery.TargetAlignment = .any

    let query: ARRaycastQuery? = sceneView.raycastQuery(from: tapLocation,
                                                    allowing: estimatedPlane,
                                                   alignment: alignment)
    
    if let nonOptQuery: ARRaycastQuery = query {

        let result: [ARRaycastResult] = sceneView.session.raycast(nonOptQuery)
        
        guard let rayCast: ARRaycastResult = result.first
        else { return }

        self.loadGeometry(rayCast)
    }
}

这是获取模型的方法:

func loadGeometry(_ result: ARRaycastResult) {

    let scene = SCNScene(named: "art.scnassets/myScene.scn")!

    let node: SCNNode? = scene.rootNode.childNode(withName: "model", 
                                               recursively: true)

    node?.position = SCNVector3(result.worldTransform.columns.3.x,
                                result.worldTransform.columns.3.y,
                                result.worldTransform.columns.3.z)

    self.sceneView.scene.rootNode.addChildNode(node!)
}