ios - 用物理创建下雨动画

Question

我目前正在开发一个 iOS 应用程序，该应用程序使用 SpriteKit 游戏技术以 Swift 编写。在这个游戏中，雨滴从屏幕顶部落到底部。当它们触及底部(由 physicsBody 表示)时，它们应该返回到屏幕顶部的原始位置，从而允许动画在游戏的生命周期内继续。

因为我只需要几滴，所以我这样创建它们:

let drop = SKSpriteNode(imageNamed: "drop")
drop.position = CGPointMake(x,y)
drop.physicsBody = SKPhysicsBody(rectangleOfSize: drop.size)
addChild(drop)

然后我创建位掩码:

drop.physicsBody!.categoryBitmask = DropCategory
bottom.physicsBody!.categoryBitmask = BottomCategory
drop.physicsBody!.contactTestBitmask = BottomCategory    

我添加了 didBeginContact 函数，当下降到达底部时我会收到通知。然后我的控制台显示“hit ground”。

func didBeginContact(contact: SKPhysicsContact) {

    var firstBody: SKPhysicsBody
    var secondBody: SKPhysicsBody

    if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
        firstBody = contact.bodyA
        secondBody = contact.bodyB
    } else {
        firstBody = contact.bodyB
        secondBody = contact.bodyA
    }

    if firstBody.categoryBitMask == BlockCategory && secondBody.categoryBitMask == GroundCategory {
        println("hit ground")

        firstBody.node?.removeFromParent()
        let drop = SKSpriteNode(imageNamed: "drop")
        drop.name = "testNode"
        drop.position = CGPointMake(self.frame.width - self.frame.width/3*2, self.frame.height) // At start Position
        drop.physicsBody = SKPhysicsBody(rectangleOfSize: drop.size)
        drop.physicsBody?.categoryBitMask = BlockCategory
        drop.physicsBody?.contactTestBitMask = GroundCategory
        addChild(drop)
    }
}

但是，水滴的位置不会改变。没有语法错误，所以我的问题是什么？

如果我替换它:

firstBody.node!.position = CGPointMake(x, y)

用这个:

firstBody.applyImpulse(CGVector)

它给了下降动力。我怎样才能使第一个选项也起作用？

Answer 1

您可以尝试在触及底部时移除节点，然后再次在顶部添加新节点。加载纹理以在单独的 SKTexture 变量中重复使用。像这样

let dropTexture = SKTexture(imageNamed: "drop.png")

这样使用

let drop = SKSpriteNode(texture: dropTexture)

然后在didBeginContact

里面

func didBeginContact(contact: SKPhysicsContact) {
    println("collided")
    var bodyA : SKPhysicsBody!
    var bodyB : SKPhysicsBody!

    if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask
    {
        bodyA = contact.bodyA!
        bodyB = contact.bodyB!
    }
    else
    {
        bodyB = contact.bodyA!
        bodyA = contact.bodyB!
    }

    if bodyA.categoryBitMask == bottomCategoryBitMask && bodyB.categoryBitMask == raindropCategoryBitMask
    {
        if bodyB.node?.parent != nil // Added line
        {
            bodyB.node?.removeFromParent()
            let drop = SKSpriteNode(imageNamed: "1.png")
            drop.name = "testNode"
            drop.position = CGPointMake(self.frame.width - self.frame.width/3*2, self.frame.height) // At start Position
            drop.physicsBody = SKPhysicsBody(rectangleOfSize: drop.size)
            drop.physicsBody?.categoryBitMask = raindropCategoryBitMask
            drop.physicsBody?.contactTestBitMask = bottomCategoryBitMask
            addChild(drop)
        }
    }
}