ios - 渲染回调时场景被修改

Question

我有以下产生错误的代码:

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

    if anchor is ARImageAnchor {  

        let phoneScene = SCNScene(named: "Phone_01.scn")!
        let phoneNode = phoneScene.rootNode.childNode(withName: "parentNode", recursively: true)!

        // rotate the phone node
        let rotationAction = SCNAction.rotateBy(x: 0, y: 0.5, z: 0, duration: 1)
        let inifiniteAction = SCNAction.repeatForever(rotationAction)
        phoneNode.runAction(inifiniteAction)          
        phoneNode.position = SCNVector3(anchor.transform.columns.3.x,anchor.transform.columns.3.y + 0.1,anchor.transform.columns.3.z)              
        node.addChildNode(phoneNode)
    }                 
}

场景在另一个场景的渲染回调中被修改。

所以我将其替换为以下内容:

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

    if anchor is ARImageAnchor {

        DispatchQueue.global().async {

            let phoneScene = SCNScene(named: "Phone_01.scn")!
            let phoneNode = phoneScene.rootNode.childNode(withName: "parentNode", recursively: true)!

            DispatchQueue.main.async {

                // rotate the phone node
                let rotationAction = SCNAction.rotateBy(x: 0, y: 0.5, z: 0, duration: 1)
                let inifiniteAction = SCNAction.repeatForever(rotationAction)
                phoneNode.runAction(inifiniteAction)
                phoneNode.position = SCNVector3(anchor.transform.columns.3.x,anchor.transform.columns.3.y + 0.1,anchor.transform.columns.3.z) 
                node.addChildNode(phoneNode)
            }  
        }
    }    
}

现在错误消失了，一切正常。我的问题是:这是正确的解决方案吗？我应该切换到后台线程来加载场景，然后切换到主线程来添加节点吗？节点是否甚至添加到主线程上？

Answer 1

在方法委托(delegate)中尝试这样的事情。这是一个旧项目的示例。

DispatchQueue.main.async {
        if let imageAnchor = anchor as? ARImageAnchor {

            let plane = SCNPlane(width: imageAnchor.referenceImage.physicalSize.width, height: imageAnchor.referenceImage.physicalSize.height)
            plane.firstMaterial?.diffuse.contents = UIColor(white: 1.0, alpha: 0.5)

            let planeNode = SCNNode(geometry: plane)
            planeNode.eulerAngles.x = -.pi
            node.addChildNode(planeNode)

            ...

        }
    }