Swift中的SpriteKit物理学 – 球滑动而不是反射

在学习SpriteKit(使用Ray Wenderlich等人的教程中使用iOS游戏)的基础上,我已经创建了我自己的非常简单的测试游戏,以了解是否可以应用我学到的概念.我决定通过使用.sks文件来创建sprite节点并替换我的手动范围检查和与物理机构的碰撞来简化我的代码.

然而,我的球保持平行于墙壁/其他矩形(如同,简单地向上和向下滑动),任何时候它们以陡峭的角度与它们碰撞.这里是相关的代码 – 我把物理属性转移到代码中,使它们更加可见：

import SpriteKit

struct PhysicsCategory {
  static let None:        UInt32 = 0      //  0
  static let Edge:        UInt32 = 0b1    //  1
  static let Paddle:      UInt32 = 0b10   //  2
  static let Ball:        UInt32 = 0b100  //  4
}

var paddle: SKSpriteNode!
var ball: SKSpriteNode!

class GameScene: SKScene,SKPhysicsContactDelegate {

  override func didMoveToView(view: SKView) {

    physicsWorld.gravity = CGVector.zeroVector

    let edge = SKNode()
    edge.physicsBody = SKPhysicsBody(edgeLoopFromRect: frame)
    edge.physicsBody!.usesPreciseCollisionDetection = true
    edge.physicsBody!.categoryBitMask = PhysicsCategory.Edge
    edge.physicsBody!.friction = 0
    edge.physicsBody!.restitution = 1
    edge.physicsBody!.angularDamping = 0
    edge.physicsBody!.linearDamping = 0
    edge.physicsBody!.dynamic = false
    addChild(edge)

    ball = childNodeWithName("ball") as SKSpriteNode
    ball.physicsBody = SKPhysicsBody(rectangleOfSize: ball.size))
    ball.physicsBody!.usesPreciseCollisionDetection = true
    ball.physicsBody!.categoryBitMask = PhysicsCategory.Ball
    ball.physicsBody!.collisionBitMask = PhysicsCategory.Edge | PhysicsCategory.Paddle
    ball.physicsBody!.allowsRotation = false
    ball.physicsBody!.friction = 0
    ball.physicsBody!.restitution = 1
    ball.physicsBody!.angularDamping = 0
    ball.physicsBody!.linearDamping = 0

    physicsWorld.contactDelegate = self
}

忘了提到这个以前,但我添加了一个简单的touchesBegan功能来调试弹跳 – 它只是调整速度来指向球在接触点：

override func touchesBegan(touches: NSSet,withEvent event: UIEvent) {
  let touch = touches.anyObject() as UITouch
  let moveToward = touch.locationInNode(self)
  let targetVector = (moveToward - ball.position).normalized() * 300.0
  ball.physicsBody!.velocity = CGVector(point: targetVector)
}

normalized()函数只是将球/触摸位置增量减小到单位向量,并且有一个减号运算符的覆盖,允许CGPoint减法.

球/边缘碰撞应该始终以正确相反的角度反射球,但是由于某种原因,球真的似乎有一个直角的东西.我当然可以实现一些解决方法来手动反映球的角度,但重要的是我想使用SpriteKit中的内置物理功能来做到这一点.有没有什么明显的,我失踪了？

ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.size.width/2)