ios - ARKit session 的 currentFrame 始终为 nil

Question

我尝试从 ARSession 的 currentFrame.camera 属性获取相机变换。

为什么我总是将 sceneView.session.currentFrame? 获取为 nil？

Answer 1

我刚刚进行了快速测试，发现 session.currentFrame 在前几次通过渲染循环时为 nil。延迟各不相同，可能是两个或十几个。但最终 currentFrame 出现了。

class ViewController: UIViewController, ARSCNViewDelegate, ARSessionDelegate, SCNSceneRendererDelegate {

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

    // Create a session configuration
    let configuration = ARWorldTrackingSessionConfiguration()
    configuration.worldAlignment = .gravityAndHeading
    configuration.planeDetection = .horizontal

    sceneView.session.delegate = self

    // Run the view's session
    sceneView.session.run(configuration)
    print(#function, sceneView.session.currentFrame)

}

// MARK: - SCNSceneRendererDelegate
func renderer(_ renderer: SCNSceneRenderer, didRenderScene scene: SCNScene, atTime time: TimeInterval) {
    print(#function, sceneView.session.currentFrame)
}

// MARK: - ARSessionDelegate
func session(_ session: ARSession, didUpdate frame: ARFrame) {
    print(#function, sceneView.session.currentFrame)
}

给我们

renderer(_:didRenderScene:atTime:) nil
...
session(_:didUpdate:) Optional(<ARFrame: 0x1c42cff10 timestamp=6334.963644 capturedImage=0x1c0124d80 camera=0x1c41262c0 lightEstimate=0x1c4238640 | no anchors, 0 features>)
...
renderer(_:didRenderScene:atTime:) Optional(<ARFrame: 0x1c02c9c30 timestamp=6334.996948 capturedImage=0x1c0124b00 camera=0x1c0124920 lightEstimate=0x1c02251a0 | no anchors, 0 features>)