重力场不起作用，物体漂浮在真空中答案

【问题标题】：Gravity field doesn't work, objects float in the vacuum重力场不起作用，物体漂浮在真空中
【发布时间】：2017-02-02 21:45:18
【问题描述】：

我试图在一个平面上有 5 个球的世界中模拟重力。我遇到的第一个问题是球穿过地板是因为它们有一个动态的身体。但是如果我使用运动体，它们就不会受到力的影响。所以我不得不使用动态物体，禁用重力并改用重力场。场景是从 COLLADA 文件加载的。这就是我设置事物的方式：

self.scene = SCNScene(named: "art.scnassets/Balls.dae")!

for i in 1...5 {
    let sphere = scene.rootNode.childNode(withName: "Sphere\(i)", recursively: true)!
    let shape = SCNPhysicsShape(geometry: sphere.geometry!, options: nil)
    let body = SCNPhysicsBody(type: .dynamic, shape: shape)
    body.mass = 0.2
    body.isAffectedByGravity = false
    body.categoryBitMask = BallCategory
    body.collisionBitMask = PlaneCategory | BallCategory | GravityFieldCategory
    sphere.physicsBody = body

    balls.append(sphere)
}

self.plane = self.scene.rootNode.childNode(withName: "Plane", recursively: true)
let shape = SCNPhysicsShape(geometry: self.plane.geometry!, options: nil)
let body = SCNPhysicsBody(type: .static, shape: shape)
body.categoryBitMask = PlaneCategory
body.collisionBitMask = BallCategory
self.plane.physicsBody = body

// Create a gravity field
let gravityField = SCNPhysicsField.linearGravity()
gravityField.categoryBitMask = GravityFieldCategory
gravityField.direction = SCNVector3Make(0.0, -1.0, 0.0)
gravityField.isActive = true
gravityField.strength = 3.0
let gravityNode = SCNNode()
gravityNode.physicsField = gravityField
self.scene.rootNode.addChildNode(gravityNode)

然后当用户触摸屏幕时，一个随机球向上移动，它应该会掉下来：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    let index = Int(arc4random_uniform(5))
    let ball = self.ball(atIndex: index)

    let moveUp = SCNAction.move(by: SCNVector3Make(0.0, 2.0, 0.0), duration: 1.5)
    ball.runAction(moveUp)
}

但它并没有掉下来，而是停在那里，漂浮在真空中。重力场不起作用。这就是发生的事情：https://youtu.be/egMe4lgPZY0

【问题讨论】：

标签： ios swift game-physics scenekit

【解决方案1】：

飞机的形状似乎不正确。我试图通过传递 nil 作为形状参数来创建飞机的物理体：

 
    self.plane = self.scene.rootNode.childNode(withName: "Plane", recursively: true) 
     let shape = SCNPhysicsShape(geometry: self.plane.geometry!, options: nil)  
    let body = SCNPhysicsBody(type: .static, shape: nil)
    body.categoryBitMask = PlaneCategory
    body.collisionBitMask = BallCategory
    self.plane.physicsBody = body

我移除了重力场并打开了球的 isAffectedbyGravity 属性。现在可以了。

【讨论】：