ios – 如何使用SpriteKit将精灵跳转到特定高度？

我正在尝试使用applyImpulse使sprite跳转到特定高度.在下面的示例代码中,动态黑色圆圈跳转到与静态红色圆圈相同的高度,但它仅适用于kludge.

如果我的物理学是正确的,那么将射弹发射到高度Y所需的初始垂直动量由质量* sqrt(2 *重力* Y)给出.然而,这个公式导致黑圈移动很少.

通过反复试验,我发现通过将脉冲矢量的垂直分量乘以12.3,我可以或多或少准确地使红色圆圈跳跃,如下面的代码所示.

这似乎是完全随意的,让我发疯.我显然做错了什么.这样做的正确方法是什么？

以下是我认为相关的代码：

let dy = mass * sqrt( 
    2 * -self.physicsWorld.gravity.dy 
    * (fixedCircle.position.y-jumpingCircle.position.y)) 
    * 12.3

jumpingCircle.physicsBody?.applyImpulse(CGVectorMake(0,CGFloat(dy)))

如果您希望复制和粘贴,这里是完整的GameScene.swift类…

import SpriteKit

class GameScene: SKScene {

var jumpingCircle = SKShapeNode()
var fixedCircle = SKShapeNode()

override func didMoveToView(view: SKView) {

    self.scaleMode = .AspectFit

    // Create an exterior physical boundary
    self.physicsBody = SKPhysicsBody(edgeLoopFromRect:self.frame)
    self.physicsWorld.gravity = CGVectorMake(0,-5);


    // Create the jumping circle
    jumpingCircle = SKShapeNode(circleOfRadius: 50)
    jumpingCircle.position = CGPoint(x: 100,y: 0)
    jumpingCircle.strokeColor = .blackColor()
    jumpingCircle.physicsBody = SKPhysicsBody(circleOfRadius: 50)
    jumpingCircle.physicsBody?.linearDamping = 0.0
    self.addChild(jumpingCircle)


    // Create the fixed circle
    fixedCircle = SKShapeNode(circleOfRadius: 50)
    fixedCircle.position = CGPoint(x: 100,y: 384)
    fixedCircle.strokeColor = .redColor()
    self.addChild(fixedCircle)

}

override func touchesEnded(touches: Set<NSObject>,withEvent event: UIEvent) {

    // to reach certain height,initial y velocity should by sqrt(2 * gravity * Y)
    // momentum required to reach this velocity is mass * velocity
    // therefore,vertical impulse should be given by mass * sqrt(2 * gravity * Y)

    if let mass = jumpingCircle.physicsBody?.mass{
        // calculate vertical impulse

        // this formula "should work" but does not
        // let dy = mass * sqrt(2 * -self.physicsWorld.gravity.dy * (fixedCircle.position.y-jumpingCircle.position.y))

        // this formula "works",but has the arbitrary multiplier
        let dy = mass * sqrt(2 * -self.physicsWorld.gravity.dy * (fixedCircle.position.y-jumpingCircle.position.y)) * 12.3

        // apply the Impulse
        jumpingCircle.physicsBody?.applyImpulse(CGVectorMake(0,CGFloat(dy)))
     }
     }
 }

let ptu = 1.0 / sqrt(SKPhysicsBody(rectangleOfSize: CGSize(width:1,height:1)).mass)

let dy = mass * sqrt(2 
    * -self.physicsWorld.gravity.dy 
    * (fixedCircle.position.y-jumpingCircle.position.y 
    * ptu))