SpriteKit物理学假阳性？(SpriteKit physics false positive?

通过didBeginContact提供的接触点并不总是在休息界定参与碰撞的物理机构的路径。其中，机构从来没有接触到这种行为的情况下最容易出问题的（如果圆节点是1px的进一步正确，接触仍然发生，虽然它是数学上是不可能。）

在图像和以下程序，该矩形具有的100像素的宽度，但接触点（在输出示出）是在101.4550 ...

import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate {


var node1:SKShapeNode
var node2:SKShapeNode
var node2PhysicsPath:CGPath
var contactPoint:SKShapeNode


required init?(coder aDecoder: NSCoder) {

    contactPoint = SKShapeNode(circleOfRadius: 10)
    contactPoint.strokeColor = SKColor(calibratedRed: 1, green: 0, blue: 0, alpha: 1)

    node1 = SKShapeNode()
    node1.position.x = 150
    node1.position.y = 200
    node1.physicsBody = SKPhysicsBody(circleOfRadius: 50)
    node1.physicsBody?.contactTestBitMask = 0xffffffff
    node1.physicsBody?.categoryBitMask = 0xffffffff
    node1.physicsBody?.usesPreciseCollisionDetection = true


    node2PhysicsPath = CGPathCreateWithRect(CGRect(x: 0, y: 0, width: 100, height: 100), nil)

    node2 = SKShapeNode()
    node2.physicsBody = SKPhysicsBody(polygonFromPath: node2PhysicsPath)
    node2.physicsBody?.dynamic = false
    node2.physicsBody?.contactTestBitMask = 0xffffffff
    node2.physicsBody?.categoryBitMask = 0xffffffff
    node2.physicsBody?.usesPreciseCollisionDetection = true

    super.init(coder: aDecoder)

    physicsWorld.contactDelegate = self
}

func didBeginContact(contact:SKPhysicsContact){
    println(contact.contactPoint);
    contactPoint.position = contact.contactPoint
    self.physicsWorld.speed = 0
    println(CGPathContainsPoint(node2PhysicsPath, nil, contact.contactPoint, true))
}

override func didMoveToView(view: SKView) {
    self.addChild(node1)
    self.addChild(node2)
    self.addChild(contactPoint)
    self.physicsWorld.gravity = CGVector(dx: 0, dy: -1.0)
}

}