我正在使用Swift和Sprite Kit在XCode Beta 6上开发游戏.
为了检测所有节点是否正在休眠,我检查他们的physicsBody.resting属性.
在更新方法中,我打印出结果.
为了检测所有节点是否正在休眠,我检查他们的physicsBody.resting属性.
在更新方法中,我打印出结果.
import SpriteKit class GameScene: SKScene,SKPhysicsContactDelegate { var hero:SKSpriteNode! override func didMoveToView(view: SKView) { self.physicsWorld.gravity = CGVectorMake(0,0) self.physicsWorld.contactDelegate = self self.physicsBody = SKPhysicsBody(edgeLoopFromRect:self.frame) hero = SKSpriteNode(imageNamed: "Spaceship") hero.position = CGPoint(x:CGRectGetMidX(self.frame),y:CGRectGetMidY(self.frame)) hero.zPosition = 10.0 hero.physicsBody = SKPhysicsBody(circleOfRadius: hero.size.width/2) hero.physicsBody.allowsRotation = false hero.physicsBody.linearDamping = 0.5 self.addChild(hero) } override func update(currentTime: CFTimeInterval) { if hero.physicsBody.resting { println("resting") } else { println("moving") } } }
令我惊讶的是,结果如下:
移动
休息
移动
(n次相同)
移动
休息
那么为什么英雄在移动,尽管我什么也没做.节点移动N次并休息(休息),之后继续移动.
谁能解释这种行为?这是一个错误还是我错过了什么?提前致谢.
如果你检查物理体的速度,你会发现它确实在移动,但速度是不可察觉的.这就是为什么没有设置休息属性.检查SKPhysicsBody是否静止的更可靠的方法是测试其线性和角速度是否几乎为零.这是一个如何做到这一点的例子:
func speed(velocity:CGVector) -> Float { let dx = Float(velocity.dx); let dy = Float(velocity.dy); return sqrtf(dx*dx+dy*dy) } func angularSpeed(velocity:CGFloat) -> Float { return abs(Float(velocity)) } // This is a more reliable test for a physicsBody at "rest" func nearlyAtRest(node:SKNode) -> Bool { return (self.speed(node.physicsBody.velocity)<self.verySmallValue && self.angularSpeed(node.physicsBody.angularVelocity) < self.verySmallValue) } override func update(_ currentTime: TimeInterval) { /* Enumerate over child nodes with names starting with "circle" */ enumerateChildNodesWithName("circle*") { node,stop in if (node.physicsBody.resting) { println("\(node.name) is resting") } if (self.nearlyAtRest(node)) { println("\(node.name) is nearly resting") } } }