Sprite Kit Physics身体休息行为 [英] Sprite Kit physicsBody.resting behavior

问题描述

我正在使用Swift和Sprite Kit在XCode Beta 6上开发游戏. 为了检测是否所有节点都在休眠，我检查了它们的physicsBody.resting属性. 在更新方法中，我打印出结果.

I am using Swift and Sprite Kit to develop a game on XCode Beta 6. In order to detect if all nodes are sleeping, i check their physicsBody.resting property. In update method i print out the result.

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，结果是:

To my surprise, the results are:

移动 休息的 移动 (n次相同) 移动 休息

moving resting moving (n times the same) moving resting

那英雄为什么要动弹，尽管我什么也没做.节点移动N次并休息一下(休息)，然后继续移动.

So why the hero is moving, although i didn't do anything. The node moves N times and takes a break(resting), after that goes on moving.

有人可以解释这种行为吗?那是一个错误还是我错过了什么?预先感谢.

Can anyone explain that behaviour? Is that a bug or do i miss something? Thanks in advance.

推荐答案

如果您检查物理物体的速度，您会发现它确实在运动，但其运动速度是无法察觉的.这就是为什么未设置静止属性的原因.检查SKPhysicsBody是否静止的一种更可靠的方法是测试其线速度和角速度是否接近零.这是如何执行此操作的示例:

If you examine the velocity of a physics body, you'll see that it is indeed moving but at a rate that is not perceivable. That's why the resting property is not set. A more reliable way to check if a SKPhysicsBody is at rest is to test if its linear and angular speeds are nearly zero. Here's an example of how to do that:

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")
        }
    }
}

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