SceneKit 相机导致对象不显示

Question

I want to be able to create a custom camera node in SceneKit and view my scene from it (instead of the default camera).

However, I've been encountering a very strange issue with SceneKit:

• If I use SCNCamera , nothing shows up in my scene.
• If I don't use SCNCamera , the objects in my scene render correctly.

This is the code I am using (very simple code; from a tutorial):

import UIKit
import SceneKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let sceneView = SCNView()
        sceneView.frame = self.view.frame
        self.view.addSubview(sceneView)

        let scene = SCNScene()

        sceneView.autoenablesDefaultLighting = true
        sceneView.allowsCameraControl = true

        let cameraNode = SCNNode()
        // If the below line of code is commented out (so no SCNCamera is added), everything shows up
        cameraNode.camera = SCNCamera()
        scene.rootNode.addChildNode(cameraNode)

        let sphere = SCNSphere(radius: 5)
        sphere.firstMaterial?.diffuse.contents = UIColor.red

        let sphereNode = SCNNode(geometry: sphere)
        cameraNode.addChildNode(sphereNode)

        sceneView.backgroundColor = UIColor.green
        sceneView.scene = scene

    }
}

This seems pretty straightforward, yet I can't find any reason why this is happening on SO, etc.

Strangely, I also observe that if I try to access the camera node via sceneView.pointOfView , I get nil , even though sceneView.allowsCameraControl is set to true

Any help is appreciated!

Answer 1

The sphere is a child node of the camera, without any offset (its position is (0, 0, 0) ) and so the camera is inside the sphere. And if the sphere's material isn't doubleSided then you won't see anything.