小编典典

Sprite Kit Physics身体休息行为

swift

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。

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:

动静(n次相同)动静

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。

谁能解释这种行为?那是一个错误还是我错过了什么?提前致谢。


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2020-07-07

共1个答案

小编典典

如果您检查一个物理物体的速度,您会发现它确实在运动,但是其速度是不可察觉的。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。这是有关此操作的示例:

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")
        }
    }
}
2020-07-07