当动态物体掉落时，它的 `_ball.position.y` 值不会改变

Question

我的问题很简单 -

func setupScene() {
        let sceneView = view as SCNView
        sceneView.backgroundColor = SKColor.blackColor()
        _scene = SCNScene()
        sceneView.scene = _scene

        sceneView.showsStatistics = true
//        Scene gravity
        sceneView.scene?.physicsWorld.gravity = SCNVector3Make(0, -70, 0)
        sceneView.scene?.physicsWorld.speed = 2.0
        sceneView.delegate = self
}

在某个时间点有 spawnBall 方法：

 func spawnBall() {
        _ball = SCNNode(geometry: SCNSphere(radius: 15))
        _ball.geometry?.firstMaterial?.diffuse.contents = UIImage(named: "ball")
        _ball.geometry?.firstMaterial?.emission.contents = UIImage(named: "ball")
        _ball.geometry?.firstMaterial?.emission.intensity = 0
        _ball.physicsBody = SCNPhysicsBody(type: SCNPhysicsBodyType.Dynamic, shape: nil)
        _ball.physicsBody?.restitution = 0.1
        _ball.physicsBody?.angularVelocity = SCNVector4(x: 1, y: 1, z: 1, w: 1)

        let position = SCNVector3Make(0, 15*10, -200)
        _ball.position = position
        _scene.rootNode.addChildNode(_ball)

    }

问题是 - 为什么当动态物体掉落时，它的 _ball.position.y 值没有改变？

我曾经 UIKit 当你移动 UIView - 它的原点改变了（我假设看到类似的东西，因为我设置 _ball.position.y = 150 它应该下降）以及如何观察它的运动？

Answer 1

它的 presentationNode 的 position 会改变。物理引擎保持模型值不变。

当动态物体掉落时，它的 `_ball.position.y` 值不会改变

when dynamic body falls down, its `_ball.position.y` value doesn't change

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